QU HAI (CH BIN) - NGUYN B LC TRN THANH PHONG - CAO NG NGUYN

GIO TRNH

HA SINH

NH XUT BN I HC HU

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M u1. Lch s, i tng, nhim v ca ho sinh th k XIX, khi m ho hc pht trin nh v bo, th ranh gii gia sinh hc v ho hc xut hin mt lnh vc khoa hc mi nhm nghin cu thnh phn ho hc ca c th sng v nhng qu trnh chuyn ho ho hc ca cc cht v ca nng lng trong qu trnh hot ng sng xy ra trong c th ca chng. Lnh vc khoa hc ny c gi l ho hc sinh vt hoc vn tt hn- ho sinh hc (biochemistry). C th ni rng, ho sinh hc l mt phn lnh vc ca khoa hc cuc sng. Nhim v ca chng nhm nghin cu cc hin tng sng bng cc phng php ho hc. y l mt khoa hc tr tui ca th k XX ang trn pht trin mnh m v ang xm nhp vo nhiu lnh vc mi nhn ca sinh vt hc, y hc v nng hc... Ho sinh hc mi tr thnh mt khoa hc c lp vo na sau th k th XIX mc du ngay t thi thng c con ngi lm quen vi nhiu qu trnh ho sinh hc trong cuc sng hng ngy ca h (nu ru, nng bnh m, thuc da, lm dm, tng, nc mm...). Tuy vy ch mi gn y, tt c mi qu trnh sinh hc ny mi c nghin cu mt cch khoa hc v c gii thch mt cch y . C th ni, s xut hin mn ho sinh hc l kt qu tt yu ca s pht trin v phi hp gia ho hc v sinh vt hc. Tnh cht v phng hng ca ho sinh hc l nghin cu trn c th sng, tm ngha chc phn ca tt c mi thnh phn, mi sn phm chuyn ho, trn c s , tm hiu su v: - Mi lin quan gia qu trnh ho hc v sinh vt hc. - Mi lin quan gia cu trc v chc nng sng ca cc c quan trong c th. - C ch iu ho ton b qu trnh sng. Tu theo i tng nghin cu m ngi ta phn chia ho sinh hc thnh ho sinh ng vt, ho sinh thc vt, ho sinh vi sinh vt v y ho sinh. Trn mi i tng, ho sinh nghin cu song song hai mt "tnh" v "ng". Vic nghin cu cc cht c trong thnh phn ca c th sinh vt l nhim v ca tnh ho sinh. Tnh ho sinh gn lin rt mt thit vi ho hc sinh hu c. y chnh l ha sinh m t. Cn vic nghin cu cc chuyn ha ho hc xy ra trong qu trnh hot ng sng ca c th ngha l nghin cu v mt ho hc ca s

12 trao i cht trong mi lin quan vi ton b c th v mi trng xung quanh l nhim v ca ng ho sinh. Tnh ho sinh v ng ho sinh lin quan vi nhau rt cht ch vic nghin cu cc qu trnh ha sinh hc s v ngha nu khng c s nghin cu cc cht tham gia trong cc qu trnh ny. Ho sinh m t gn lin vi s pht trin ca ho hu c. Cui th k XVIII, u th k XIX, hng lot cc hp cht hu c c tch ra t thc vt v t cc t chc ng vt: citric acid, malic acid, tatric acid, oxalic acid, urea v cc alkaloid. Ngi ta xc nhn rng trong thnh phn ca tt c cc cht bo u cha glycerin. Trong thi gian ny, Lavoisier cng gii thch c c ch ho hc ca s h hp v s chy. ng chng minh rng, lng nhit do cc c th sng sn sinh ra cng bng lng nhit thu c khi t chy cc cht dinh dng bn ngoi c th (khi h hp trong c th, carbon v hydrogen b oxy ha t t, qu trnh ny rt ging s chy bnh thng). Tip theo cc cng trnh chit xut, tinh ch v phn tch cc cht hu c l nhng cng trnh nghin cu tng hp cc cht hu c. Quan im cho rng, vt cht sng khc vi vt cht khng sng b nh hon ton khi m Whler vo nm 1828 iu ch c carbamid (urea) bng phng php nhn to t cc cht v c. Pht minh ca Whler l bng chng cho rng to nn cht sng khng cn thit bt k mt "lc" sng no (vis vitalis) v nh vy m ng hng cho ho sinh pht trin. (Thi k ny khoa hc i su vo s sng ang b khng ch v km hm bi thuyt "hot lc" cho rng cc cht hu c tham gia vo cu to ca c th sinh vt ch c th to ra bi mt "ng siu t nhin"). Trong sut khong hai th k trc, s pht trin ca ho sinh hc xy ra tng i chm. S bt u tht s ca ho sinh hc thng c coi l vo nm 1866 khi Tbigen thnh lp b mn ho sinh u tin di s lnh o ca Hoppe - Seyler ( nc c). S u tin ca tp ch mang tnh cht ho sinh hc c ra mt vo nm 1877 (Hoppe - Seyler's Zeitschrift fr physiologische Chemie). Tin ca n l s hot ng ca Liebig c v trng phi ho hc hu c ca ng. Bng cch s dng cc phng php nghin cu mi, Liebig xc nh thnh phn ca nhiu thc phm, chia cc cht cha trong thc phm thnh protein, glucid, lipid v xc nh hm lng nitrogen trong protein. Sau nhng cng trnh nghin cu ca Pasteur v s ln men, cc nh khoa hc ch nhiu n bn cht enzyme vn xc tc cho cc qu trnh khc nhau trong c th sng. Nhiu cng trnh c gi tr khc, trong c cng trnh ca Fischer i vo cu trc v tng hp glucid, lipid, amino acid v

13 protein, Pavlov trong thi gian ny nghin cu cc c ch enzyme v Miescher th nghin cu nucleic acid. Thi gian ny ngi ta cng pht hin ra vitamin. Vic xc lp nn thnh phn ho hc ca thc vt, vic pht hin ra cc enzyme v vic lm sng t vai tr ca chng trong s trao i cht, s pht hin ra vitamin v hormon, s pht trin ca ho hc v amino acid v protein, v glucid, lipid to iu kin cho vic hnh thnh ng ho sinh v chnh nh s pht trin ca ng ho sinh m ngi ta xy dng c nhng quan im thng nht v cc quy lut chung ca cc qu trnh trao i cht v ca nhng chuyn ho nng lng trong c th sinh vt. Ngy nay chng ta bit r rng, tt c cc cht xy dng nn t bo sng, u thay i khng ngng. c trng ca s sng l s bin i ho hc. Nh vy ho sinh hc hin i trc ht l ng ho sinh. Trc tin l nhng hin tng trao i cht, l s chuyn ho v phn gii cc cht dinh dng nhm thu nhn nng lng ho hc cng nh xy dng vt cht ca t bo. Cc phn ng ho hc ny c xy ra nh tc dng xc tc ca nhng enzyme, v vy vic nghin cu cc enzyme chim mt phn quan trng trong ho sinh hc. Th n thuc v ng ho sinh l iu ho ho hc. iu ny c xy ra trn con ng cc sn phm trao i cht xc nh, thng l cng vi s tham gia ca nhng cht c bit l hormon c to thnh trong cc tuyn ni tit. Th ba thuc v ng ho sinh l cc qu trnh ho hc c xy ra gn lin vi cc cu trc v thc hin cc chc nng ca cc phn t cu trc. Vic xc nh trnh t ca amino acid trong protein v cu trc khng gian ca protein (Sanger, Perutz v Kendrew) cng nh cu trc ca nucleic acid (Chargaff, Watson v Crick) l bt u mt giai on mi trong s pht trin ca ho sinh hc tc l thi k ca sinh hc phn t. Mt iu r rng l khng th tch ring sinh hc phn t v ho sinh hc ra khi nhau. V c bn m ni th "sinh hc phn t" ch l tn mi, nhng l mt phn ngnh ring ca ho sinh. N c gng lm sng t cc hin tng sng c bn trn c s phn t c ngha l trn c s ho sinh hc. Chnh v vy theo quan nim hin i th ho sinh hc l khoa hc nghin cu c s phn t ca s sng. 2. Thnh phn ho hc ca c th sng Trong c th sng, nc l thnh phn quan trng nht. Tr mt s m hoc loi t bo (cc ht thc vt, cc bo t m xng, m m), lng nc ca chng khng t n 80%, cn lng nc ca mt s sinh vt khc cng vt qu 90% (ton b lng nc ca c th con

14 ngi khong 50-70%). iu cn lu l mt s dng sng bc thp, cc virus, cc bo t sng qua trng thi kh ho hon ton, song trong trng thi khng c nc th cc hot ng sng ca chng b hon li. T cc c s trn chng ta c th ni rng cc qu trnh ho hc c trng cho s sng c xem nh l nhng phn ng tin hnh trong mi trng nc. Ngoi ra ngi ta pht hin c hn 60 nguyn t c trong c th sng. Cc nguyn t ny c trong c th vi nhng lng rt khc nhau. Mt s c coi l nhng nguyn t cn thit xy dng c th v phc v cho s pht trin bnh thng ca c th; mt s khc th chc nng sinh hc ca chng cha c bit r; s cn li c coi nh do s xm nhp ngu nhin. C H O N S P Cl Ca Mg K Na u l nhng nguyn t rt cn thit i vi c th sng, 11 nguyn t ny chim gn 100% khi lng ton phn ca thc vt v ng vt. Nhng nguyn t dng vt c gi l yu t vi lng, vai tr quan trng ca chng i vi cuc sng cng dn dn c sng t l nhng ion kim loi nng Co, Zn, Mn, Mo; trong trng hp cc c th ng vt bc cao cn c I, cc cy xanh th c B. Cn nh rng, tr I v Mo, cc nguyn t c k n u nm trong s 30 nguyn t u ca h thng tun hon v hn mt na cc nguyn t c s th t n 30 c vai tr sinh hc quan trng. Nhiu hp cht hu c trc y c coi nh l ring bit thuc gii sinh vt, nay cng c nghin cu, tng hp trong phng th nghim. l cc protein, nucleic acid, glucid, lipid, enzyme v vitamin. y l nhng cht chim v tr hng u trong sinh hc v cng chnh l i tng nghin cu chnh ca cc chng trong gio trnh ny. 3. Mi quan h ca ho sinh vi cc ngnh khoa hc ca sinh hc, nng nghip v y hc Trong sinh hc c nhiu ngnh, nhng nghin cu sinh hc ngy nay l nghin cu mc phn t. Ho sinh l khoa hc nghin cu s sng mc phn t, cho nn c th ni bt c chuyn ngnh no ca sinh hc nh ng vt hc, thc vt hc, vi khun hc, sinh l hc, t bo hc, m phi hc... u cn phi trang b kin thc v k thut ho sinh nghin cu khoa hc chuyn ngnh mnh. Do khi ni n cc chuyn ngnh ca sinh hc hin i th trc ht phi ni n ho sinh trong nhng nm gn y. Ngay c cng ngh gen, cng ngh enzyme cng chnh l lnh a ca ho sinh. Chng hn i vi ng vt, thc vt, vi sinh vt, ngy nay mun nghin cu phn loi chnh xc cc ging chng cng phi dng cc ch tiu phn t mt s protein, enzyme hay nucleic acid trong ty lp th. i vi nng nghip mun tng nng sut cy trng phi ch n qu trnh ho sinh quang hp, qu trnh ho sinh ny mm,

15 qu trnh ho sinh pht dc, qu trnh chuyn ho, sinh tng hp cc cht to nn ht, qu, qu trnh tc ng ho sinh ca cc cytokinin n s sinh trng v pht trin ca cy. i vi vt nui cng vy, mun c nng sut tht, sa, trng cao, ngi chn nui phi hiu c cc qu trnh ho sinh pht trin n tng giai on pht trin ca con vt, n tng b phn c bp, bung trng ca chng c s tc ng mnh m. i vi y dc hc, vn ch cht nghin cu bnh nguyn, bnh l, chn on v iu tr bnh cng u lin quan cht ch n ho sinh, tc lin quan n s thay i cc phn t bnh l xy ra trong c th v tm nhng cht hot tnh sinh hc c tc dng phng chng hoc cha khi bnh. V vy c th ni ho sinh l gc, l c bn gip hiu su sc cc khoa hc khc ca sinh hc, nng nghip v y hc. 4. Mt s thnh tu ni bt ca ha sinh trong thi gian gn y Trong qu trnh pht trin ca mnh, nhiu ngnh nh ca ho sinh ra i.V ho sinh mt s chc phn h thng quan trng c ho sinh min dch, ho sinh di truyn, c bit mt ngnh mi gn y xut hin l cng ngh ho sinh. Cc lnh vc nh ca ho sinh ng gp mt cch tch cc vo thnh tch chung ca ho sinh. Nhiu gii thng Nobel ghi cng cc kt qu nghin cu quan trng, m ra nhiu cnh ca mi cho s pht trin ca ho sinh nh ho sinh ca h thng min dch ca Snell, Bena Cerraf v Dausset nm 1980. Cng nm y Paul Berg cng c gii thng Nobel bi cng trnh nghin cu gn cc mu DNA. Nm 1981-1982, thnh tu tng hp gen - interferon gm 514 i base bi Leicester c thc hin. T n nay hng lot cng trnh khc v nghin cu ho sinh c p dng trong lnh vc khoa hc. Gn y, nm 1997 gii thng Nobel y hc trao cho Staley Prusiner v cng trnh nghin cu prion, mt khi nim mi v "nhim khun", gy bnh no th xp ngi v ng vt. Prion (PrP) l protein tn ti hai dng ng phn alpha v bta. c th kho mnh th PrP c dng alpha cn khi c th b bnh th dng alpha b dui ra v xp thnh cc bng song song gi l PrP bta. Dng ny rt bn vi enzyme tiu ho v khng b ph hu nhit cao (n 200oC). Do vy prion nh l tc nhn gy bnh hon ton mi c b sung vo danh sch nhng tc nhn gy bnh nh virus, vi khun, nm. Cng trnh ny a ra khi nim bnh l phn t hon ton mi trong sinh hc v y hc. Cng trnh khng ch pht hin ra tc nhn gy bnh xp no m cn t nn mng cho s tm hiu c ch mt tr lin quan n bnh gi v bnh Alzheimer, cng nh t nguyn tc cht ch cho vic ghp cc c quan ph tng ca ng vt cho con ngi v thuc men ch t ng vt dng cho ngi.

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TI LIU THAM KHOTi liu ting Vit1. Trn Th n (ch bin). 1979. Ha sinh i cng (tp I, II). NxB KH&KT. H Ni. 2. i Duy Ban. 2005. Ha sinh hc v ha sinh y hc. Ha sinh hc. 1: 8-13. 3. Phm Th Trn Chu, Trn Th ng. 2000. Ha sinh hc. Nxb Gio dc. H Ni. 4. L Don Din. 1975. Ha sinh thc vt. Nxb Nng nghip. H Ni 5. Nguyn Tin Thng, Nguyn nh Huyn. 1998. Gio trnh sinh ha hin i. Nxb Gio dc. H Ni. 6. Nguyn Xun Thng, o Kim Chi, Phm Quang Tng, Nguyn Vn ng, 2004. Ha sinh hc. Nxb Y hc, H Ni.

Ti liu ting nc ngoi1. Karlson. P., 1972. Biokmia. Medicina Knyv Kiad Budapest. 2. Lehninger A.L., 2004. Principle of Biochemistry, 4th Edition. W.H Freeman. 3. Stryer L., 1981. Biochemistry. W.H.Freeman and company. San Francisco. 4. Straub .F. B. 1965. Biokmia. Medicina Knyv Kiad Budapest.

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Li ni uHa sinh hc l khoa hc nghin cu thnh phn ha hc ca c th sng v nhng qu trnh chuyn ha ha hc ca cc cht v nng lng trong qu trnh hot ng sng xy ra trong c th sinh vt. L ngnh khoa hc c bn, ng thi cng l mt khoa hc ng dng, l ngnh khoa hc c s cho cc khoa hc c bn quan trng khc nh cng ngh sinh hc, sinh hc phn t; ha sinh hc tc ng ln hay ni rng hn l mi nhn nh hng v gii quyt cc vn phc v cho nng, lm, ng nghip, phc v cho y hc... Chnh v vy, ha sinh hc khng ch l cng c ca sinh hc m cn l cng c ca cc chuyn ngnh khc lin quan n sinh hc nh nng, lm, ng, y dc. Gio trnh nhm cung cp cho sinh vin cc ngnh, chuyn ngnh lin quan n sinh hc trong i hc Hu nhng kin thc c bn v cu to v thnh phn ha hc ca cc sinh cht, mi lin quan gia cu trc v chc nng, cc qu trnh chuyn ha ca chng v nng lng trong c th sinh vt. Cun sch c bin son theo chng trnh gio dc i hc c i hc Hu ph duyt, bi tp th tc gi ca cc trng i hc khoa hc, s phm thuc i hc Hu. Sch cng c th dng ti liu tham kho cho sinh vin cc trng khc, nhng ngi chun b thi tuyn sau i hc cng nh cc cn b nghin cu lin quan. Cc tc gi xin cm n nhng ng nghip gp nhiu kin b ch trong qu trnh bin son. c bit cc tc gi xin chn thnh cm n GS.TSKH L Don Din - Gim c Trung tm T vn u t Nghin cu pht trin Nng thn Vit Nam (INCEDA), Ch tch Hi Ha sinh Vit Nam nhn phn bin v cho rt nhiu nhng li khuyn qu bu nhm hon thin gio trnh. Vi thi gian bin son v kinh nghim cn hn ch, cun sch cn cha tht y v chc chn khng trnh khi nhiu thiu st. Chng ti rt mong nhn c nhng kin ng gp ca cc bn ng nghip, sinh vin v bn c ln xut bn sau s c hon thin hn. Thay mt cc tc gi Ch bin

PGS.TS Qu Hai

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Chng 1

SaccharideL hp cht hu c c to nn t cc nguyn t: C, H, O c cng thc cu to chung Cm(H2O)n, thng m = n. Do c cng thc cu to nh trn nn saccharide thng c gi l carbohydrate - c ngha l carbon ngm nc. Tuy nhin c nhng saccharide c cng thc cu to khng ng vi cng thc chung ni trn v d: deoxyribose (C5H10O4). C nhng cht khng phi l saccharide nhng c cng thc cu to ph hp vi cng thc chung trn v d : acetic acid (CH3COOH). Saccharide l thnh phn quan trng trong mi sinh vt . thc vt, saccharide chim t 80 - 90% trng lng kh, saccharide tham gia vo thnh phn cc m nng , v d cellulose, hay tch tr di dng thc phm d tr vi lng ln, v d tinh bt. ng vt, hm lng saccharide thp hn nhiu, thng khng qu 2%, v d glycogen.

1.1. Monosaccharide1.1.1. Cu to v danh php L cht c cha nhiu nhm ru v mt nhm kh oxy (nhm kh l nhm carbonyl l aldehyde hay ketone). - Nhm kh l aldehyde ta c ng aldose v c cng thc tng qut: CHO (CHOH)n CH2OH - Nhm kh l ketone ta c ng ketose c cng thc tng qut: CH2OH C= O (CHOH)n CH2OH

18 CHO - CH2OH c xem nh l monosacchariden gin nht. Trong thin nhin monosaccharide c cha t 2 n 7 carbon v c gi tn theo s carbon (theo ting Hy Lp) + ose V d: monosaccharide c 3C gi l triose. Tng t ta c tetrose, pentose, hexose, heptose. 1.1.2. ng phn quang hc Quy c Fischer: Fischer l ngi u tin nu ra nguyn tc biu din cc monosaccharide bng cng thc hnh chiu ca chng. Theo : hnh chiu ca cc nguyn t carbon bt i (C*) v cc nguyn t C khc nm trn mt ng thng, nguyn t C c s th t nh nht c hnh chiu nm trn cng. Cn cc nhm th c hnh chiu bn phi hay bn tri. V d : glyceraldehyde. V glyceraldehyde c 1 C* nn theo quy tc ca Vant Hoff c 2 ng phn (N = 2n) 1CHO 1CHO HO- 2C* -H3CH2OH

H-2C*-OH3CH2OH

D: -OH bn phi L: -OH bn tri

L glyceraldehyde D glyceraldehyde. Khi phn t monosaccharide c nhiu C* th cng thc c dng D hay L c cn c vo v tr nhm OH ca C* xa nhm carbonyl nht. V d : CHO CHO H-C-OH HO-C-H H-C-OH H-C-OH CH2OH D glucose H-C-OH HO-C-H H-C-OH HO-C-H CH2OH L glucose

19 Ch : monosaccharide t triose tr ln u c C* tr dihydoxy aceton CH2OH C=O CH2OH 1.1.3. Cng thc vng ca monosaccharide Cng thc thng theo Fischer nh trnh by trn khng ph hp vi mt s tnh cht ho hc ca chng nh: mt s phn ng ho hc thng xy ra vi aldehyde khng xy ra i vi monosaccharide . V vy c th ngh rng nhm -CHO trong monosaccharide cn tn ti di dng cu to ring bit no . Mt khc: monosaccharide c th to ether vi methanol to thnh mt hn hp 2 ng phn c cng nhm methoxy (- OCH3). iu chng t trong monosaccharide cn tn ti mt nhm -OH c bit. Qua nghin cu Kolle cho thy: s ng phn thu c ca monosaccharide thc t nhiu hn s ng phn tnh theo cng thc N=2n, do gii thch cc hin tng trn, Kolle cho rng ngai dng thng monosaccharide cn tn ti dng vng. S to thnh dng vng xy ra do tc dng ca nhm -OH cng phn t monosaccharide to thnh dng hemiacetal hay hemiketal.

20 V d : cu to vng ca glucose xy ra nh sau:

Do s to thnh hemiacetal vng m C1 tr nn C*, nhm -OH mi c to ra C1 l -OH glucoside. Tng t vi ketose th C2 tr nn C*, nhm -OH mi c to ra C2 l -OH glucoside khi to thnh hemiketal. Cch biu din cng thc vng nh trn da vo nguyn tc ca Haworth: C v cu ni vi oxy nm trn mt mt phng , cc nhm th cng thc thng nm bn phi th cng thc vng nm di mt phng v ngc li. Ring cc nhm th ca C c nhm OH dng to cu ni oxy th theo quy tc ngc li. 1.1.4. Hin tng h bin ca monosaccharide Nh ta thy, khng th gii thch c tt c cc tnh cht ca monosaccharide nu ta ch tha nhn mt dng cu to no ca monosaccharide. Nn ngi ta cho rng cc dng cu to c th chuyn ho ln nhau. pyranose pyranose Dng thng Furanose Furanose

21 1.1.5. Tnh cht ca monosaccharide 1.1.5.1. L tnh Cc monosaccharide tan trong nc, khng tan trong dung mi hu c, c tnh quay cc tr biose v khng c C*. 1.1.5.2. Ho tnh a. Monose l tc nhn kh Trong mi trng kim, kh cc ion kim loi nng c ho tr cao thnh ion c ha tr thp hay cc ion kim loi thnh kim loi. Tnh kh ny do nhm aldehyde hay nhm ketone to ra v cc monose bin thnh acid. V d: Cu2+ b bin i thnh Cu+ trong phn ng vi thuc th Fehling, Ag+ b bin i thnh Ag trong phn ng trng gng. b. Phn ng vi cc cht oxy ho Tu thuc vo cht oxy ho: - Cht oxy ho nh nh nc brom ng aldose s thnh aldonic acid, vi ketose phn ng khng xy ra. - Cht oxy ho mnh nh HNO3 m c c s oxy ho xy ra 2 u cho ta di acid. - Trng hp c bit nu ta bo v nhm -OH glucoside bng cch methyl ha hay acetyl ho trc khi oxy ho bng nc brom, sn phm to thnh l uronic acid. c. Phn ng vi cht kh D dng vng chim t l rt ln trong thnh phn, dng thng chim t l nh nhng cho ta thy r tnh cht ca mt carbonyl tht s. Khi b kh: monose s bin thnh polyalcohol. d. Phn ng to furfural Di tc dng ca acid m c, cc aldopentose to thnh furfural v aldohexose bin thnh hydroxymethylfurfural. Cc sn phm ny khi cho tc dng vi cc phenol cho mu c trng nh: naphthol cho vng mu tm (Molisch). y l phn ng phn bit ng vi cc cht khc. Nu ng 5C s cho mu xanh cm thch vi orcinol (Bial). e. Phn ng ester ho Cc gc ru ca monose c kh nng kt hp vi acid to thnh ester. Cc ester phosphate thng gp l: Glucose-6-phosphate, fructose6-phosphate...

22 1.1.6. Cc monose quan trng 1.1.6.1. Pentose

1.1.6.2. Hexose Cc hexose quan trng nh: * Glucose: cn gi l dextrose v lm quay mt phng nh sng phn cc v pha phi. Ph bin rng ri trong thc vt nht l trong qu nho, nn cn gi l ng nho, trong mu ngi c 0.8 - 1,1 g/l, nhng ngi b bnh i ng c th n 2g/l. Cc disaccharide quan trng l saccharose, lactose, maltose v cc polysaccharide quan trng l tinh bt, glycogen. Ngi ta s dng glucose trong y hc nh cht tng lc. * D - Mannose: t gp trng thi t do, thng gp trong polysaccharride v glucoside * D - Galactose: l thnh phn ca lactose c trong sa cn gi l ng no tu. Chng l thnh phn cu to ca raffinose, hemicellulose. pectine... * D - Fructose cn gi l levulose v lm quay mt phng nh sng phn cc v pha tri. Fructose cn gi l ng qu, c trng thi t do trong tri cy chn v mt ong. Chng l thnh phn ca disaccharide saccharose. Trong c th ta cn thy dng ester vi phosphoric acid ng vai tr quan trng trong trao i cht. Fructose c ngt rt ln, dng c ngt bng 1/3 dng .

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1.2. Oligosaccharide1.2.1. Disaccharide S to thnh disaccharide l do s kt hp ca 2 monose cng loi hay khc loi nh lin kt glucosidic. Lin kt glucosidic c th c to thnh gia -OH glucoside ca monose ny vi -OH glucoside ca monose kia, hay gia mt nhm -OH glucoside ca monose ny vi -OH ( khng phi -OH glucoside) ca monose kia. Disaccharide ch c tnh kh khi t nht mt trong 2 nhm -OH glucoside trng thi t do. Ngha l disaccharide s khng c tnh kh khi 2 nhm -OH glucoside lin kt vi nhau. Cc disaccharide quan trng * Maltose do 2 phn t - D-glucose lin kt vi nhau v tr C1 C4 to thnh. Cng thc cu to:

Maltose c nhm -OH glucoside trng thi t do nn c tnh kh. Maltose c nhiu trong mm la v mch nha (maltum) nn gi n l maltose. * Lactose (ng sa) do mt phn t D-galactose lin kt vi mt phn t D- glucose v tr C1- C4.

* Saccharose do mt phn t D-glucose lin kt vi mt phn t D-fructose v tr C1-C2. Do n khng c tnh kh, cn gi l ng ma v c nhiu trong ma. D b thy phn khi un nng.

25

1.2.2. Trisaccharide L oligosaccharide c cha 3 monosaccharide, ph bin trong thin nhin l raffinose. Cng thc cu to nh sau: -D-galactopyranosyl 1-2 -D glucopyranosyl 1-2 -D fructofuranose. Do c cng thc nh trn nn khng c tnh kh oxy. D b thy phn, di tc dng ca fructofuranosidase s to thnh fructose v melobiose vi galactosidase s to thnh galactose v saccharose.

1.3. PolysaccharideCn gi l glycan, ty thnh phn monose c trong polysaccharide ngi ta chia chng ra lm: homopolysaccharide (ch cha mt lai monosaccharide) v heteropolysaccharide (c t nht 2 lai monosaccharide).

26 Polysaccharide ng vai tr quan trng trong i sng ng vt, thc vt. Mt s polysaccharide thng gp nh tinh bt, glycogen, cellulose... 1.3.1. Polysaccharide thc vt 1.3.1.1. Tinh bt L polysaccharide d tr ca thc vt, do quang hp to thnh. Trong c v ht c t 40 n 70% tinh bt, cc thnh phn khc ca cy xanh c it hn v chim khong t 4 n 20%. Tinh bt khng ha tan trong nc, un nng th ht tinh bt phng ln rt nhanh to thnh dung dch keo gi l h tinh bt. Tinh bt c cu to gm hai phn: amylose v amylopectin, ngoi ra cn c khong 2% phospho di dng ester. T l amylopectin/amylose cc i tng khc nhau l khng ging nhau, t l ny go np l ln hn go t. *Amylose Chim 15 n 25% lng tinh bt, do nhiu gc D- glucose lin kt vi nhau thng qua C1-C4 to thnh mch thng khng phn nhnh. Trong khng gian n cun li thnh hnh xon c v c gi bn vng nh cc lin kt hydro. Theo mt s ti liu trong amylose cn c cha cc D- glucopyranose dng thuyn.

Amylose bt mu xanh vi iodine, mu ny mt i khi un nng, hin mu tr li khi ngui. Mt c trng ha l khc cn ch l n b kt ta bi ru butylic.

27

Ht tinh bt trong lc lp amylose

* Amylopectin Cu to do cc phn t D- glucose lin kt vi nhau, nhng c phn nhnh. Ch phn nhnh l lin kt C1-C6 glucosidic.

28

1.3.1.2. Cellulose c cu to bi nhng phn t D-glucose lin kt vi nhau bng lin kt 1-4 glucosidic. Chng l thnh phn ch yu ca vch t bo thc vt. i vi ngi th cellulose khng c gi tr dinh dng v cellulose khng b thy phn trong ng tiu ha. Mt s nghin cu cho thy n c vai tr trong iu ha tiu ho. ng vt n c thy phn c cellulose nh enzyme cellulase. Cellulose khng tan trong nc, tan trong dung dch Schweitzer. Khi un nng vi H2SO4, cellulose s b thy phn thnh cc phn t D-glucose. Cellulose c dng hnh si di, nhiu si kt hp song song vi nhau thnh chm nh cc lin kt hydro, mi chm (micelle) cha khang 60 phn t cellulose. Gia cc chm c nhng khong trng, khi ho g khong trng ny cha y lignin v ta xem lp lignin ny nh l mt lp cement. Lignin l cht trng hp ca coniferylic alcohol

Cc gc -OH ca cellulose c th to ester vi acid v d: to nitro cellulose vi HNO3 , to acetyl cellulose vi CH3COOH.

29 1.3.1.3. Hemicellulose Tn gi chung cho lp polysaccharide thng i theo vi cellulose trong thc vt. Hemicellulose khng tan trong nc, tan trong dung dch kim v thy phn bng acid d hn cellulose. Khi b thy phn hemicellulose to thnh mt hn hp gm cc hexose v pentose hay ch mt mnh hexose m thi. Trong hemicellulose khi monose no chim a s th hemicellulose c tn tng ng vi monose : Xylose chim a s th hemicellulose c tn l Xylan, Arabinose chim a s th hemicellulose c tn l Araban, Galactose chim a s th hemicellulose c tn l Galactan... Xylan c nhiu trong rm r, trong mt s c quan ca thc vt, galactose c nhiu trong rm, g v cc loi ht. 1.3.1.4. Inulin L polysacchride d tr ca thc vt c trng lng phn t khong 5000-6000, do nhng phn t D- fructose lin kt vi nhau bng lin kt 1-2 v tn cng bng mt phn t saccharose. Inulin c tm thy trong c thc dc khong 40%. Ngi ta x dng inulin sn xut fructose. xc nh inulin ngi ta thy phn n v xc nh bng phn ng nh tnh Seliwanoff. 1.3.1.5. Pectin L loi polysaccharide c nhiu trong qu , c v thn cy, thnh phn chnh l galacturonic acid c nhm -COOH b methyl ha. Ngi ta s dng rng ri pectin trong sn xut keo. 1.3.2. Polysaccharide ng vt 1.3.2.1. Glycogen L polysaccharide d tr ng vt c tm thy trong gan v c, hin nay cn tm thy trong mt s thc vt nh ng, nm. C cu to ging amylopectin nhng phn nhnh nhiu hn, b thu phn bi phosphorylase ( c coenzyme l pyrydoxal phosphate), ct lin kt 1-6 cn enzyme debranching. Sn phm cui cng l cc phn t glucose-1-P.

30 Pha ngoi glucose lin kt 1-6

Mch chnh

ht glycogen t bo gan

1.3.2.2. Hyaluronic acid C cng thc cu to c lp li t n v sau:

Hyaluronic acid c trng lng phn t rt ln, c th ln n nhiu triu, hyaluronic acid rt ph bin v l thnh phn quan trng ca m lin kt, c tm thy trong dch khp xng, trong thy tinh th mt, n tc dng nh mt lp cement bo v bn trong t bo chng li s xm nhp ca vi khun cng nh cc cht l khc. khp xng n lm

31 cho dch c tnh trn gip c ng khi b au. Hyaluronic acid b thy phn bi hyaluronidase, enzyme ny c tm thy trong vi khun gy bnh, trong tinh trng. Hyaluronidase to d dng cho tinh trng i vo non ca bun trng, mt khc n cng l yu t gip cho cc cht khc v vi khun gy bnh i vo cc m trong c th. 1.3.2.3. Chondroitin L heteropolysaccharide, thnh phn khng th thiu c m xng sn.

1.3.2.4. Heparin Heteropolysaccharide c tc dng chng li s ng mu v ngn chn s bin i prothrombin thnh thrombin.

GlcA2S hoc IdoA2S

1.3.3. Mt s polysaccharide ph bin khc 1.3.3.1. Chitin L homopolysaccharide, c v s, c, cc loi cn trng v nm mc. N c cu to nh sau:

32

1.3.3.2. Dextran c tm thy vi khun v nm men, cu to mch chnh l Dglucose1-6, nhnh l 1-3 v thnh thong c nhnh 1-2 hay 1-4. Do c cu to 1-6 nn i vi ng vt, dextran khng b phn gii hay b phn gii rt chm.

33 Dextran c di v hnh dng ging albumin, ngi ta thng dng nhit thy phn khng hon ton dextran nhm thay th protein ca huyt tng , dung dch 10% ca n hon ton trong sut. Trong cng ngh ngi ta tng hp dextran v c gi l sephadex s dng trong tch tng phn protein.

TI LIU THAM KHOTi liu ting Vit1. Phm Th Trn Chu, Trn thi ng. 1999. Ho sinh hc, NXB Gio dc, H Ni. 2. Qu Hai. 2004. Gio trnh Ha sinh i cng, Ti liu lu hnh ni b Trng HKH Hu. 3. Trn Thanh Phong.2004. Gio trnh Ha sinh i cng, Ti liu lu hnh ni b Trng HKH Hu. 4. L Ngc T (ch bin), L Vn Ch, ng Th Thu, Phm Quc Thng Nguyn Th Thnh, Bi c Hi, Lu Dun, L Don Din, 2000. Ha sinh Cng nghip, Nxb KH&KT, H Ni.

Ti liu ting Anh1. Gilbert H. F. 1992. Basic concepts in biochemistry, Copyright by the Mcgraw- Hill companies, Inc. 2. Lehninger A. L. 2004. Principles of Biochemistry, 4th Edition. W.H Freeman.

34

Chng 2

LipidCng nh saccharide, protein, lipid l cht hu c phc tp, ta c th nh ngha nh sau: * nh ngha rng: Lipid l cht tan c trong dung mi hu c, khng tan trong nc, nh ngha ny khng phn nh ht tnh cht ca cc lipid v: - C lipid khng tan c trong dung mi hu c nh phospholipid khng tan trong aceton. - Nhng cng c cht khng phi lipid nhng tan c trong dung mi hu c. * nh ngha hp: Lipid l ester ca ru v acid bo. Tuy nhin c nhng lipid do acid bo lin kt vi ru bng lin kt peptide. * nh ngha dung ho: Lipid l nhng cht chuyn ho ca acid bo v tan c trong dung mi hu c. Lipid rt ph bin ng vt cng nh thc vt v tn ti di 2 dng m nguyn sinh cht (dng lin kt) v dng d tr (dng t do). - M nguyn sinh cht: thnh phn ca mng t bo cng nh cc bo quan khc v d: ty th, lp th... dng ny khng b bin i ngay c khi con ngi b bnh bo ph hoc b i. - Dng d tr (dng t do) c tc dng cung cp nng lng cho c th, bo v cc ni quan, l dung mi cn thit cho mt s cht khc. Cn c vo thnh phn nguyn t c mt, ngi ta chia lipid ra lm 2 loi * Lipid n gin: trong phn t ch cha C, H, O. * Lipid phc tp: ngoi C, H, O cn c mt s nguyn t khc nh N, P, S.

2.1. Lipid n gin2.1.1. Glycerid Glycerid l ester ca ru glycerol v acid bo, l m d tr ph bin ng vt v thc vt.

35

1- Stearoyl, 2- linoleoyl, 3-palmitoyl glycerol, mt triacylglycerol hn tp

2.1.1.1. Glycerol L triol khng mu, v ngt nhn. Khi t glycerol hay lipid c cha glycerol vi cht ht nc s to acrolein c mi kht. 2.1.1.2. Acid bo Acid bo thng gp l nhng acid bo c s carbon chn, mch thng, c th no hay khng no v chui C xp theo hnh ch chi. Tuy nhin cng c nhng acid bo ngoi nhm chc acid cn cha nhng nhm chc khc nh ru, ketone, mch carbon c vng hay nhnh. a. Acid bo chn, thng, no: CH3(CH2)nCOOH C4 CH3 -(CH2)2 COOH butylic acid c nhiu trong c. C6 CH3 -(CH2)4 -COOH caproic acid c trong b, sa d. C8 CH3 - (CH2)6-COOH caprylic acid c trong b, sa d. C10 CH3-(CH2)8 COOH capric acid c trong b, sa d.

36 C12 n=10 lauric acid c trong du da. C14 n=12 myristic acid c trong du da. C16 n=14 palmitic acid c trong du ng vt,thc vt. n=16 stearic acid c trong du ng vt,thc vt. C18 C20 n=18 arachidic acid c trong du lc. b. Acid bo chn, thng, khng no - Cha mt ni i (C): 10 9 C 16 (9-10): CH3-(CH2)5 -CH = CH- (CH2)7COOH Palmitoleic acid : Tm thy trong du thc vt. C18 (9-10): CH3-(CH2)7 -CH = CH- (CH2)7 COOH Oleic acid: acid ny c ba ng phn. C18 (6-7): Petroselenic acid C18 (11-12): Vaccenic acid. C18 (12-13): Heparic acid - Acid bo c 2 ni i (C): C18 (9-10,12-13): Linoleic acid CH3-(CH2)4 -CH = CH- CH2-CH=CH-(CH2)7-COOH C th khng tng hp c acid ny m ly t ngoi vo. Ngy xa ngi ta quan nim acid ny l vitamin v gi l vitamin S. Nhng thc cht l mt acid bo m c th cn vi mt lng ln. - Acid bo c cha 3 ni i (C): C18((9-10,12-13,15-16): Linolenic acid, c th khng tng hp c acid ny. - Acid bo c 4 ni i (C): C20 (5-6,8-9,11-12,14-15): Arachidonic acid. Ngoi ra cn c cc acid bo c cha ni ba nhng khng quan trng. c. Acid bo c cha chc ru Thng gp trong lipid phc tp v cha nhm ru gn chc acid nn c tn l - hydroxy... R-CH-COOH OH

37 V d: - hydroxy lynoceric acid CH3 -(CH2 )21- CH-COOH OH Ricinoleic acid CH3-(CH2)5 - CH - CH2 - CH = CH- (CH2)7 - COOH10 9

OH d. Gc R trong phn t acid c nhnh v c s C l Phocenic acid: Undecylonic acid : e. Acid bo c vng * Chaulmoogric acid: CH3 CH CH2 COOH CH3 CH2 = CH - (CH2)8 - COOH - (CH2)12 - COOH

* Sferculic acid:

CH3 - CH2 - C = C - (CH2)7 - COOH

CH2 2.1.1.3. Tnh cht ca acid bo v triglyceride * Tnh cht vt l: a. im tan chy im tan chy ph thuc vo s C ca acid bo, acid bo c chui C di th im tan chy cao v ngc li. Nhng acid bo c C l c im tan chy thp hn acid bo c s C nh hn n 1 n v . Ngoi ra tan chy cn ph thuc vo s ni i trong phn t acid bo, acid bo cha nhiu ni i th im tan chy cng thp. b. si Acid bo c chui C di th si cng cao, thng p dng tnh cht ny tch cc acid bo ra khi nhau. c. Tnh ho tan - Trong nc: acid bo c chui C ngn (4,6,8) d tan, C10 kh tan, C12 khng tan. Nu acid bo dng mui th d ha tan hn. - Trong dung mi hu khng phn cc nh benzen, ether, ether du ho acid bo d tan.

38 - Trong dung mi hu c phn cc nh aceton, acid bo kh ho tan hay ho tan rt t. * Tnh cht ho hc: a. S hydrogen ho Acid bo cha no c th kt hp vi H2 to thnh acid bo no R - (CH2)n - CH =CH- (CH2)n - COOH + H2 R - (CH2)n -CH2 - CH2 - (CH2)n - COOH Ngi ta dng phn ng ny ch to thc phm nh margarin. b. S halogen ho Acid bo khng no kt hp vi cc nguyn t thuc h halogen (F, Cl, Br, I) to thnh acid bo no. R - (CH2)n - CH = CH- (CH2)n - COOH + I 2 R - (CH2)n - CH - CH- (CH2)n - COOH I I C th dng phn ng ny xc nh s ni i trong phn t acid bo. Phn ng d dng hay kh xy ra tu thuc vo v tr ni i i vi nhm carboxyl, ni i cng gn nhm carboxyl phn ng cng kh xy ra. xc nh s ni i ngi ta cn c vo ch s Iod. Ch s Iod: L s gam Iod cn thit tc dng ln 100gam cht bo. Do ch s iod cng ln th s ni i cng nhiu. c. S thu phn: Ester nn khi thu phn s to thnh ru glycerol v acid bo. Tc nhn thy phn l acid, kim, nc hay enzyme. * Thy phn bng nc cn nhit v p sut cao. * Thy phn bng kim: NaOH hay KOH Ch s x phng ho: s mg KOH cn thit trung ho 1g cht bo Do ch s x phng cng ln th di mch cng ngn, nn c dng xc nh di ca mch C. xc nh tnh cht ca cht bo ngi ta cn cn c vo mt s ch s khc nh ch s acid. Ch s acid: s mg KOH dng trung ho tt c acid bo t do c trong 1g cht bo.

39 * Thu phn bng enzyme: trong c th lipid b thu phn bng enzyme lipase. - Lipase dch trng tc dng vo v tr . - Lipase ty tng tc dng vo v tr v . d. S i ha: Du m lu c mi v v kh chu gi l s i ha, mt trong nhng nguyn nhn gy ra l do oxy khng kh kt hp vo ni i to thnh peroxide. Nu oxy kt hp vo nguyn t carbon ng cnh lin kt i th s to thnh hydrogen peroxide. Sau peroxide v hydrogen peroxide s b phn gii to thnh aldehyde v ketone. Cc aldehyde v ketone ny u l nhng cht c mi v v kh chu. 2.1.2. Cerid Cng l ester ca ru v acid bo, nhit thng th rn, c ng thc vt, thc vt n thng to thnh mt lp mng ph ln l, thn, qu ca cy. Cng thc tng qut: R O CO R Ru trong cerid l ru cao phn t, ch cha mt nhm OH , mnh C khng phn nhnh, rt t khi mch C c vng V d: Ru cetol:CH3 - (CH2)14-CH2OH. Sp ong, sp c voi (spermaceti) l ester ca ru cetol v palmitic acid.

Ngoi ra trong sp ong v sp c voi cn c ru t do, acid bo t do v hydrocarbon. 2.1.3. Sterid L ester ca ru sterol v acid bo. Ru sterol c vng v trng lng phn t rt ln, sterol tiu biu l cholesterol, acid mt. Acid bo thng l palmitic, oleic, ricinoleic.

40 2.1.3.1.Cholesterol Cholesterol bao gm nhn phenanthrene kt hp vi cyclopentan to thnh cyclopentanoperhydrophenanthrene. Cholesterol c mang nhm ru C3, ni i C5 - C6 v 2 gc CH3 C10, C13 v mt nhnh isooctan C17. Cholesterol ch c ng vt, trong mu c khong 2.10-3, c nhiu trong c, nhng m l lch, gan, da cng c cha cholesterol hay cc cht chuyn ho ca n. Cholesterol c tm thy u tin sn mt, sn mt l do s dn mt n rut non b nghn, mt cha nhiu cholesterol nn kt ta li thng sn mt. Cholesterol l cht quan trng trong s sinh tng hp acid mt, vitamin D v nhiu cht khc. Cholesterol + acid bo cholesterid

Trong thin nhin, cc sterol trng thi t do nhiu hn trng thi sterid. c th ngi, ch 10% sterol b ester ha to thnh sterid. T l sterol v sterid cc m khc nhau l khng ging nhau. * L tnh ca cholesterol: kt tinh di dng vy ng nh nh x c, dng kt tinh cng khc nhau tu theo mi trng kt tinh. * Ho tnh: - Phn ng vi acid bo do nhm -OH C3. - B hydrogen ha hay halogen ho C5 - C6.

41 - Phn ng mu: + Phn ng Liebermann: Cholesterol cho mu xanh lc, mu ny rt bn trong nhiu gi, phn ng ny c dng xc nh cholesterol bnh vin. + Phn ng Salkowski: Cholesterol cho vnh mu . 2.1.3.2. Acid mt: Acid mt c tm thy trong ng vt c v gm 3 dng sau: cholic acid, deoxycholic v chenodeoxycholic acid. Acid mt l cht c i vi ngi. V vy trong mt, acid mt lin kt vi acetamin to thnh mt cht t c hn. Ngoi cholesterol v acid mt cn c cc sterol khc cng c ngun gc ng vt nh hormone nang thng thn, hormone tuyn sinh dc, cc sterol c ngun gc thc vt nh ergosterol, stigmasterol...

2.2. Lipid phc tpKhc vi lipid t do c nhim v cung cp nng lng , hm lng lun thay i. Lipid phc tp c nhim v tham gia xy dng cc cu t ca t bo, hm lng khng thay i hay rt t thay i. 2.2.1. Glycerophospholipid (phosphatid) Chng ta c th hnh dung cu to chung ca glycerophospholipid nh sau:

Glycerophospholipid l diester ca phosphoric acid. Mt pha phosphoric acid lin kt vi glycerol, pha kia lin kt vi X. Ty cu to ca X ta c cc loi glycerophospholipid khc nhau:

42

Lecithin: Lc X l choline nn lecithin cn c gi l choline phosphatid

Lecithin c nhiu trong lng trng g, trong u nnh, trong mu, trong cc dy thn kinh. Qua cu to ta nhn thy n gm 2 phn - Phn phn cc bao gm phosphoric acid v base nitrogen a nc.

43 - Phn khng phn cc bao gm cc gc acid bo, ru glycerol ght nc. Do c cu to nh trn nn lecithin trong nc s to thnh dung dch gi l dung dch gi. Nh c tnh va a nc, va ght nc m hnh nh phospholipid tham gia trong vic bo m tnh thm mt chiu ca cc mng cu trc di t bo. Lecithin c th b thu phn bng acid, kim hay enzyme: * Thu phn bng acid: tt c lin kt ester u b ct t. * Thu phn bng kim: ta c acid bo dng mui, glycerophosphate v choline. Nhng choline b phn hy cho trimetylamin. Vi kim nh ch c th ct lin kt ester gia ru v acid bo. * Thu phn bng enzyme: c 4 loi enzyme lecithinase A, B, C v D tc ng ln cc lin kt ester khc nhau: B CH2O - CO - R1 A CHO - CO - R2 C OH CH2O - PO D Lecithinase A ct lin kt v tr ca lecithin cho acid bo v lisolecithin. Cephalin: Trong cu to ca cephalin X l colamine. CH2O-CO-R1 CHO-CO- R2 O CH2O-P = O O-CH2- CH2 -H3N+

44

Tng t lecithin, cephalin (X l ethanolamine) c cu tao gm hai phn a nc v ght nc, l thnh phn ca dy thn kinh v c nhiu trong no. Lisocephalin c to thnh khi ct lin kt ester v tr , cng c tnh cht ph hy hng cu nh lisolecithin. Serinphosphatid: Gi l serinphosphatid khi X l serine. Trong c th: lecithin, cephalin, serinphosphatid thng gp dng hn hp bi c s bin i tng h gia serine, choline v colamine. 2.2.2. Sphingophospholipid y l lipid phc tp, trong ru a nguyn t l sphingosine. Acid bo lin kt vi ru sphingosine bng lin kt peptid. Ty theo X ta c cc loi sphingophospholipid khc nhauAcid bo

Sphingophospholipid quan trng nht l sphingomyelin, y X l: phosphocholine. Acid bo trong sphingomyelin l lignoceric, palmitic,

45 stearic hay nervonic. Sphingophospholipid l diaminophospholipid, khc vi phosphatid l monoaminophospholipid. Sphingophospholipid khng tan trong ethylic ether, da vo tnh cht ny tch chng ra khi hn hp lipid 2.2.3.Glycolipid Glycolipid l lipid phc tp khng cha phospho, trong thnh phn ca chng c cha hexose, thng l galactose hay cc dn xut ca galactose, i khi l glucose. Thuc nhm ny c MGDG, DGDG v sulfolipid kh ph bin trong lc lp v cc thnh phn khc ca t bo l.

6-Sulfo-6-deoxy--D-glucopyranosyldiacyglycerrol (sulfolipid)

2.2.4. Sphingolipid Cerebroside: trong phn t cerebroside ru sphingosine lin kt vi acid bo bng lin kt peptide, vi galactose (X) bng lin kt glucosidic.

46 Cc cerebroside khc nhau v thnh phn acid bo, c nhiu trong m thn kinh, hng cu, bch cu, tinh trngAcid bo

Ganglyoside: cu to ging cerebroside nhng X l phc hp oligosaccharide

Phc hp ologosaccharide

TI LIU THAM KHOTi liu ting Vit1. Phm Th Trn Chu, Trn thi ng. 1999. Ho sinh hc, NXB Gio dc, H Ni. 2. Qu Hai.2004. Gio trnh Ha sinh i cng, Ti liu lu hnh ni b Trng HKH Hu. 3. Trn Thanh Phong.2004. Gio trnh Ha sinh i cng, Ti liu lu hnh ni b Trng HKH Hu. 4. L Ngc T (ch bin), L Vn Ch, ng Th Thu, Phm Quc Thng Nguyn Th Thnh, Bi c Hi, Lu Dun, L Don Din, 2000. Ha sinh Cng nghip, Nxb KH&KT, H Ni.

Ti liu ting Anh1. LehningerA.L. 2004. Principles of Biochemistry, 4th Edition. W.H Freeman. 2. Mead, Alfin-Slater, Howton & Popjk. 1986. Lipids: Chemistry, biochemistry and nutrion, Plenum, New York.

47

Chng 3

ProteinProtein l hp cht hu c c ngha quan trng bc nht trong c th sng, v mt s lng, protein chim khng di 50% trng lng kh ca t bo; v thnh phn cu trc, protein c to thnh ch yu t cc amino acid vn c ni vi nhau bng lin kt peptide. Cho n nay ngi ta thu c nhiu loi protein dng tinh th v t lu cng nghin cu k thnh phn cc nguyn t ho hc v pht hin c rng thng thng trong cu trc ca protein gm bn nguyn t chnh l C, H, O, N vi t l C 50%, H 7%, O 23% v N 16%. c bit t l N trong protein kh n nh (li dng tnh cht ny nh lng protein theo phng php Kjeldahl bng cch tnh lng N ri nhn vi 6,25). Ngoi ra trong protein cn gp mt s nguyn t khc nh S 0-3% v P, Fe, Zn, Cu... Phn t protein c cu trc, hnh dng v kch thc rt a dng, khi lng phn t (MW) c tnh bng Dalton (1Dalton = 1/1000 kDa, c l kiloDalton) ca cc loi protein thay i trong nhng gii hn rt rng, thng thng t hng trm cho n hng triu. v d: insulin c khi lng phn t bng 5.733; glutamat-dehydrogenase trong gan b c khi lng phn t bng 1.000.000, v.v... T lu ngi ta bit rng protein tham gia mi hot ng sng trong c th sinh vt, t vic tham gia xy dng t bo, m, tham gia hot ng xc tc v nhiu chc nng sinh hc khc. Ngy nay, khi hiu r vai tr to ln ca protein i vi c th sng, ngi ta cng thy r tnh cht duy vt v ngha ca nh ngha thin ti ca Engels P. Sng l phng thc tn ti ca nhng th protein. Vi s pht trin ca khoa hc, vai tr v ngha ca protein i vi s sng cng c khng nh. Cng vi nucleic acid, protein l c s vt cht ca s sng.

3.1. Amino acid3.1.1 Cu to chung Amino acid l cht hu c m phn t cha t nht mt nhm carboxyl (COOH) v t nht mt nhm amine (NH2), tr proline ch c nhm NH (thc cht l mt imino acid).

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Trong phn t amino acid u c cc nhm COOH v NH2 gn vi carbon v tr . Hu ht cc amino acid thu nhn c khi thu phn protein u dng L- amino acid. Nh vy cc protein ch khc nhau mch nhnh (thng c k hiu: R).

Hnh: 3.1. Cng thc cu to chung ca cc amino acid

3.1.2. Phn loi amino acid Hin nay ngi ta phn loi amino acid theo nhiu kiu khc nhau, mi kiu phn loi u c ngha v mc ch ring. Tuy nhin, h u da trn cu to ho hc hoc mt s tnh cht ca gc R. V d c ngi chia cc amino acid thnh 2 nhm chnh l nhm mch thng v nhm mch vng. Trong nhm mch thng li tu theo s c mt ca s nhm carboxyl hay s nhm amine m chia ra thnh cc nhm nh, nhm amino acid trung tnh (cha mt nhm COOH v mt nhm NH2); nhm amino acid kim (cha mt nhm COOH v hai nhm NH2); nhm amino acid acid (cha hai nhm COOH v mt nhm NH2). Trong nhm mch vng li chia ra thnh nhm ng vng hay d vng v.v... C ngi li da vo tnh phn cc ca gc R chia cc amino acid thnh 4 nhm: nhm khng phn cc hoc k nc, nhm phn cc nhng khng tch in, nhm tch in dng v nhm tch in m. Tuy nhin, hin nay cch phn loi cc amino acid ang c nhiu ngi s dng nht l da vo gc R ca amino acid v c chia lm 5 nhm: Nhm I. Gm 7 amino acid c R khng phn cc, k nc, l: glycine, alanine, proline, valine, leucine, isoleucine v methionine. (Hnh 3.2)

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Hnh 3.2. Cng thc cu to ca cc amino acid nhm I

Nhm II. Gm 3 amino acid c gc R cha nhn thm, l phenylalanine, tyrosine v tryptophan (Hnh 3.3.)

Hnh 3.3. Cng thc cu to ca cc amino acid nhm II

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Nhm III. Gm 5 amino acid c gc R phn cc, khng tch in, l serine, theonine, cysteine, aspargine v glutamine (Hnh 3.4)

Hnh: 3.4. Cng thc cu to ca cc amino acid nhm III

Nhm IV. Gm 3 amino acid c R tch in dng, l lysine, histidine v arginine, trong phn t cha nhiu nhm amin (hnh 3.5).

Hnh 3.5. Cng thc cu to cc amino acid nhm IV

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Nhm V. Gm 2 amino acid c gc R tch in m, l aspartate v glutamate, trong phn t cha hai hm carboxyl (hnh 3.6).

Hnh 3.6. Cng thc cu to ca cc amino acid nhm V

3.1.3. Cc amino acid thng gp Cc amino acid thng gp l nhng amino acid thng c mt trong thnh phn ca cc loi protein. Chng c khong 20 loi v c thu nhn khi thu phn protein. Cc loi amino acid ny c tn gi, khi lng phn t v k hiu c trnh by trn bng 3.1. 3.1.4. Cc amino acid khng th thay th Cc amino acid c hnh thnh bng nhiu con ng khc nhau. Nh bit, trong phn t protein c khong 20 loi amino acid, tuy nhin trong c th ngi v ng vt khng tng hp c tt c cc loi m phi a t ngoi vo qua thc n. Nhng amino acid phi a t ngoi vo c gi l cc amino acid khng th thay th. Ngi ta bit c c khong 8-10 loi amino acid khng th thay th bao gm: Met, Val, Leu, Ile, Thr,Phe, Trp, Lys, Arg v His v ngy nay ngi ta cn xem Cys cng l mt amino acid khng th thay th. 3.1.5. Cc amino acid t gp Ngoi cc amino acid thng gp trn, trong phn t protein i khi cn c mt s amino acid khc, l nhng loi t gp. Cc amino acid ny l dn xut ca nhng amino acid thng gp nh: trong phn t collagen c cha 4-hydroxyproline l dn xut ca proline, 5hydroxylysine l dn xut ca lysine v.v...Mt khc, mc d khng c trong cu trc protein, nhng c hng trm loi amino acid khc cng c th tn ti dng t do hoc lin kt vi hp cht khc trong cc m v t

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bo, chng c th l cht tin thn hay l cc sn phm trung gian ca qu trnh chuyn ho trong c th. Bng 3.1. Cc amino acid thng gpTn amino acid Glycine Alanine Proline Valine Leucine Isoleucine Methionine Tyrosine Tryptophan Serine Threonine Cysteine Aspargine Glutamine Lysine Histidine Arginine Aspartate Glutamate Tn amino acid gi theo danh php ho hc -aminoacetic acid -aminopropionic acid -pyrolydilcarboxylic acid -aminoisovaleric acid -aminoisocaproic acid -amino--metylvaleric acid -amino--metylthiobutyric acid -amino-hydroxyphenylpropionic acid -amino--indolylpropionic acid -amino--hydoxypropionic acid -amino--hydroxybutiric acid -amino--thiopropionic acid amid ca aspartate amid ca glutamate , diaminocaproic acid -amino--imidazolpropionic acid -amino--guanidinvaleric acid -aminosuccinic acid -aminoglutarate Tn vit tt Gly Ala Pro Val Leu Ile Met Phe Tyr Trp Ser Thr Cys Asn Gln Lys His Arg Asp Glu K hiu G A P V L I M F Y W S T C B Q K H R D E Khi lng (MW) 75 89 115 117 131 131 149 165 181 204 105 119 121 132 146 146 155 174 133 147

Phenylalanine -amino--phenylpropionic acid

3.1.6. Mt s tnh cht ca amino acid 3.1.6.1. Mu sc v mi v ca amino acid Cc amino acid thng khng mu, nhiu loi c v ngt kiu ng nh glycine, alanine, valine, serine, histidine, tryptophan; mt s loi c v ng nh isoleucine, arginine hoc khng c v nh leucine. Bt

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ngt hay cn gi l m chnh l mui ca natri vi glutamic acid (monosodium glutamate). 3.1.6.2. Tnh tan ca amino acid Cc amino acid thng d tan trong nc, cc amino acid u kh tan trong alcohol v ether (tr proline v hydroxyproline), chng cng d ho tan trong acid v kim long (tr tyrosine). 3.1.6.3. Biu hin tnh quang hc ca amino acid

Hnh 3.7. ng phn lp th ca alanine

Cc amino acid trong phn t protein u c t nht mt carbon bt i (tr glycine) v th n u c biu hin hot tnh quang hc, ngha l c th lm quay mt phng ca nh sng phn cc sang phi hoc sang tri. Quay phi c k hiu bng du (+), quay tri c k hiu bng du (-). Gc quay c hiu ca amino acid ph thuc vo pH ca mi trng. Tu theo s sp xp trong cu trc phn t ca cc nhm lin kt vi carbon bt i m cc amino acid c cu trc dng D hay L (hnh 3.7) gi l ng phn lp th. S ng phn lp th c tnh theo 2n (n l s carbon bt i) Hu ht cc amino acid khc hp th tia cc tm bc sng () khong t 220 - 280 nm. c bit cng nng 10-3M, trong bc sng khong 280 nm, tryptophan hp th nh sng cc tm mnh nht, gp 4 ln kh nng hp th ca tyrosine (hnh 3.8) v phenylalanine l yu nht.

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Phn ln cc protein u cha tyrosine nn ngi ta s dng tnh cht ny nh lng protein hp ph

- Bc sng(nm)Hnh 3.8. Ph hp th nh sng cc tm ca tryptophan v tyrosine

3.1.6.4. Tnh lng tnh ca amino acid Trong phn t amino acid c nhm carboxyl -COOH nn c kh nng nhng proton (H+) th hin tnh acid, mt khc c nhm amin- NH2 nn c kh nng nhn proton nn th hin tnh base. V vy amino acid c tnh cht lng tnh. Trong mi trng acid, amino acid dng cation (tch in dng), nu tng dn pH amino acid ln lt nhng proton th nht chuyn qua dng lng cc (trung ho v in), v tip tc tng pH amino acid s nhng proton th hai chuyn thnh dang anion (tch in m). V vy i khi ngi ta coi n nh mt di-acid.

cation

lng cc

anion

Hnh 3.9. Tnh lng tnh ca amino acid

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Tng ng vi phn ly H+ ca cc nhm COOH v NH3+ c cc tr s pK1 v pK2 (biu th phn ly ca cc nhm c 1/2). T trc tin chuyn sang dng lng tnh v sau cng chuyn thnh dng anion.

phn ly ca H+Hnh 3.10. ng cong chun ca glycine nng 1 M 25OC

Ngi ta xc nh c pHi (pI= pH ng in) = pK1 + pK2 / 2. V d khi ho tan glycine vo mi trng acid mnh th hu nh glycine u dng cation. Nu tng dn lng kim, thu c ng cong chun . Trn ng cong chun thy rng glycine ln lt nhng 2 proton trc Tng ng phn ly ca nhm COOH c mt na c tr s pK1= 2,34 v phn ly ca NH3+ c mt na c tr s pK2= 9,60. Nh vy ta c 2,34 + 9,60 pHi = = 5,97 2

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Bng: 3.2 Cc tr s pK ca cc amino acid thng gp Tn cc amino acid Glycine Alanine Proline Valine Leucine Isoleucine Methionine Phenylalanine Tyrosine Tryptophan Serine Theonine Cysteine Aspargine Glutamine Lysine Histidine Arginine Aspartate Glutamate Cc tr s pK pK1(ca COOH) pK2(ca NH+3) pKR(ca R) 2,34 2,34 1,99 2,32 2,36 2,36 2,28 1,83 2,20 2,38 2,21 2,11 1,96 2,02 2,17 2,18 1,83 2,17 1,88 2,19 9,60 9,60 10,96 9,62 9,60 9,68 9,21 9,13 9,11 9,39 9,15 9,62 10,28 8,80 9,13 8,95 9,17 9,04 9,60 9,67 5,97 6,01 6,48 5,97 5,98 6,02 5,74 5,48 5,66 5,89 5,68 5,87 5,07 5,41 5,65 9,74 7,59 10,76 2,77 3,22 pI

10,07

8,18

10,53 6,00 12,48 3,65 4,25

Mt khc ti pK1 + 2 s phn ly H+ ca nhm COO- glycine l 99%, ch 1% dng COOH v pK2 -2 dng NH3+ l 99%, ch 1% dng NH2. Nh vy trong vng pH t pK1 + 2 n pK2 -2, phn t glycine ch yu dng lng tnh v kt qu ta c mt vng ng in. Ngoi ra cc amino acid trong gc R c thm nhm COOH hay NH2 s phn ly ca chng s c thm mt tr s phn ly na-pKR (xem bng 3.2). 3.1.7. Cc phn ng ho hc ca amino acid Cc amino acid u c nhm NH2 v COOH lin kt vi C, v vy chng c nhng tnh cht ho hc chung. Mt khc cc amino acid khc nhau bi gc R, v vy chng c nhng phn ng ring bit. Ngi ta chia cc phn ng ho hc ca amino acid thnh 3 nhm:

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- Phn ng ca gc R Do cc amino acid c cu to gc R khc nhau, nn ngi ta c th dng xc nh tng amino acid ring r nh phn ng c trng ca n, v d phn ng oxy ho kh do nhm SH ca cysteine, phn ng to mui do cc nhm COOH hay NH2 ca glutamate hay lysine, phn ng to ester do nhm OH ca tyrosine v.v... - Phn ng chung L phn ng c s tham gia ca c hai nhm - COOH v - NH2. Tt c cc amino acid trong phn t protein u phn ng vi hp cht ninhydrin to thnh phc cht mu xanh tm, ring imino acid nh proline to thnh mu vng. Phn ng c thc hin qua mt s bc nh sau: Di tc dng ca ninhydrin nhit cao, amino acid to thnh NH3, CO2 v aldehide, mch polypeptide ngn i mt carbon; ng thi ninhydrin chuyn thnh diceto oxy hindriden. Diceto oxy hindriden, NH3 mi to thnh tip tc phn ng vi mt phn t ninhydrin khc to thnh phc cht mu xanh tm (hnh 3.11)

Hnh 3.11. Phn ng ca protein vi ninhydrin

- Phn ng ring bit C th chia cc phn ng ring bit theo hai nhm - COOH v - NH2 + Cc phn ng ca nhm - COOH. Ngoi cc phn ng ca nhm COOH thng thng to ester, to amid, to mui ...th n cn c nhng phn ng c trng khc nh c th b kh thnh hp cht ru amino di s xc tc ca NaBH4. R-NH2CH-COOH R-NH2CH-CH2OH Nhm COOH c th to thnh phc aminoacyl-adenylate trong phn ng hot ho amino acid tng hp protein, hay c th loi CO2 vn gp rt nhiu trong qu trnh thoi ho amino acid.

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+ Cc phn ng ca nhm - NH2. Nhiu phn ng ca nhm amine c dng nh tnh v nh lng cc ch tiu ca amino acid nh: nh lng nitrogen ca amino acid ngi ta cho phn ng vi HNO2 gii phng N2. R-CH-COOH + HNO2 NH2 R-CH-COOH OH + N2 + H2O

nh lng amino acid ngi ta cho phn ng vi aldehyde to thnh base schiff. xc nh amino acid u N-tn cng ngi ta cho tc dng vi 2-4 dinitrofluobenzen (phn ng Sanger) hay phenyliothiocyanate (phn ng Edman).

3.2. Peptide3.2.1. Khi nim chung Peptide l nhng protein thng c cu trc on ngn khong t hai n vi chc amino acid ni vi nhau, c khi lng phn t thng di 6.000. Chng c th c tng hp trong t nhin hoc c hnh thnh do s thoi ho protein. Trong cc peptide cc amino acid c lin kt vi nhau thng qua lin kt peptide (hnh 3.12).

Hnh 3.12. S to thnh lin kt peptide

Lin kt peptide c bn cao bi cu trc ca n c 4 e', 2e' thuc v lin kt C=O cn 2e' thuc v b i e' t do ca nguyn t N. Lin kt gia C-N l lin kt phc tp, n c th chuyn t dng n

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dng lai (trung gian) th b mt phn ghp i ca lin kt (hnh 3.13). Ngi ta cho rng t l ca lin kt kp ny l khong 30% i vi lin kt C-N v 70% vi lin kt gia C v O. Nh vy u ca mt chui peptide l amino acid c nhm -amine (-NH2) t do c gi l u Ntn cng v u kia c nhm - carboxyl ( -COOH) t do c gi l u C tn cng. Lin kt peptide to nn b khung chnh ca chui polypeptide, cn cc gc R to nn mch bn ca chui (hnh 3.14)Dng cng ho tr Dng ion +

Dng lai (hybrid)

Hnh 3.13. S tn ti cc dng ca lin kt peptide

Mch chnh

Mch bn Hnh 3.14. Mch bn v khung ca mt chui polypeptide

3.2.2. Cc phng php xc nh peptide Ngoi phn ng ca nhm NH2 v COOH u tn cng, cc gc R ca peptide cng cho nhng phn ng mu c trng ca cc amino acid t do tng ng. Mt trong nhng phn ng mu c trng nht dnh cho lin kt peptide l phn ng Biure, phn ng ny khng xy ra vi

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amino acid t do v vi dipeptide. Trong mi trng kim mnh, lin kt peptide phn ng vi CuSO4 to thnh phc cht mu tm (hnh 3.15.) v c kh nng hp th cc i bc sng 540 nm. y l phn ng c s dng rng ri nh lng protein. Phng php xc nh protein theo Lowry cng da trn nguyn tc ca phn ng ny bng cch thm thuc th Folin-Ciocalteau lm tng nhy ca phn ng sau khi thc hin phn ng biure, ng thi da vo cc gc Tyr, Try nh thuc th to phc mu xanh da tri. OC =NH HN C NH HN O Cu O C OHN = C NH

Hnh 3.15. Phc mu tm trong phn ng Biure

C mt s phng php tch phn lp v xc nh thnh phn, s lng v trnh t amino acid trong peptide. V nguyn tc chung cc phng php tch phn lp v xc nh peptide v c bn cng nh i vi protein. Tuy nhin peptide l nhng on ngn ca chui polypeptide, v th c th b qua giai on ct chui polypeptide thnh cc peptide nh m c th tch, phn lp ngay bng phng php in di hay sc k tch ring tng peptide. Sau khi tch ring cc peptide, tin hnh thu phn hon ton thnh cc amio acid t do, xc nh cc amino acid , amino acid u N-tn cng v amino acid u C-tn cng. Cc d liu thu c qua s phn tch ny s c so snh i chiu v tng hp li. V d, Puppy v Bodo phn tch mt peptide ca dch khi thu phn Cytocrom C thu c cc d kin sau y: - Thnh phn amino acid ca peptide sau khi c thu phn hon ton v tin hnh sc k l 2Cys, 1 Ala, 2 Glu, 1His, 1Thr, 1Val,v 1Lys.

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- Dng phng php Sanger xc nh c amino acid u N-tn cng l Cys v phng php carboxypeptidase xc nh c amino acid u C - tn cng l Lys. - Cu to ca peptide nh (bng cch thu phn tng phn ban u v xc nh cc amino acid, amino acid u N - tn cng v amino acid u C - tn cng ca mi peptide nh): Cys- Ala Cys-(Ala,Glu) Ala- Glu Glu- Cys Cys- His Glu (Cys, His) (Val- Glu) Thr (Val, Glu) Glu- Lys Thr (Val, Glu, Lys) Tng hp cc d kin trn, h xc nh c trnh t cc amino acid ca peptide nghin cu l: H2N-Cys-Ala-Glu-Cys-His-Thr-Val-Glu-Lys-COOH. y l nguyn tc chung xc nh mt trnh t trong peptide. Tuy nhin i vi nhng peptide di, vic xc nh rt phc tp. 3.2.3. Cc peptide thng gp trong thin nhin Trong t nhin tn ti nhiu dng peptide c chc phn quan trong lin quan n hot ng sng ca c th nh l cc hormon, cc cht khng sinh hay nhng cht tin thn ca t bo vi khun v.v... Bn cnh cng c nhng peptide chc phn cha r rng, c nhng peptide l sn phm thu phn ang cn dang d ca protein. Trong phm vi ca gio trnh ny xin c gii thiu mt s peptide quan trng,c nhiu ngha i vi cho hot ng sng ca sinh vt. 3.2.3.1. Glutathion v cc cht tng t Glutathion l mt tripeptide -glutamyl-cysteyl-glycine c cng thc cu to nh sau: NH2 CH2 SH

HOOC-CH-CH2-CH2-CO-NH-CH-CO-NH-CH2-COOH Trong cu trc ca glutathion, nhm SH ca cysteine l nhm hot ng, v vy ngi ta thng vit tt ch glutathion l G-SH. y l glutathion dng kh. Trong mi trng hot ng glutathion c th

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nhng hydrogen (H) thnh dng oxy ho (GSSG) v ngc li c th nhn H thnh dng kh: 2GSH-2H +2H

G-S-S-G

Nh phn ng trn, glutathion ng vai tr ca mt h thng oxy ho kh (vn chuyn hydrogen). Glutathion l mt trong nhng peptide ni bo ph bin nht, n phn b nhiu trong cc m v cc c quan nh: gan, thn, lch, tim, phi, hng cu v.v... 3.2.3.2. Cc hormone sinh trng (HGH) Hormone sinh trng ca ngi (HGH-human growth hormone) cn c tn gi STH (somatotropin hormone) l mt chui polypeptide bao gm 191 amino acid c khi lng phn t 20.000. Trong cu trc c hai cu disulfua c to thnh gia amino acid 53 -165 v gia amino acid 182-189. Hot ng sinh hc ca HGH l chui gm 134 amino acid. HGH c cu to rt ging vi hormon lactogen ca rau thai (85% amino acid ging nhau) v gn ging prolactin ca ngi (32% amino acid ging nhau). Hormon sinh trng c tc dng i vi s tng trng ni chung, kch thch s to sn hn l to xng, n cng l mt hormon chuyn ho. Hormon sinh trng kch thch s tng hp protein t nhng amino acid c vn chuyn d dng vo trong t bo nh chng, v l hormon gy tng ng huyt, sinh i tho ng, ng thi kch thch s thoi ho lipid m bo nhu cu v nng lng cho c th, gy tng acid bo t do trong huyt tng. S thiu ht HGH nu xy ra trc tui dy th s dn n chng ngi ln, s d tha HGH nu xy ra trc tui dy th s dn n chng ngi khng l, nu xy ra sau tui dy th s dn n chng ngi b to cc (pht trin chiu dy ca u, xng v mt).

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3.2.3.3. Insulin T 1953, Sanger (gii thng Nobel 1958) nghin cu, tinh ch v xc nh hon ton cu trc ca phn t insulin. Phn t insulin bao gm 51 amino acid, c cu trc gm 2 chui polypeptide, vi khi lng phn t 5.700 chui A c 21 amino acid, chui B c 30 amino acid. Hai chui c ni vi nhau bng 2 cu disulfua. Trong chui A cng hnh thnh 1 cu disulfua gia amino acid th 6 v amino acid th 11. Phn c hiu (c trng ca mt loi) ch tp trung vo cc amino acid th 8-9-10, 12-14 ca chui A v c bit l amino acid th 30 ca chui B (hnh 3.16). Ngi ta cng xc nh c cu trc ba chiu ca insulin v thy rng cu trc phn t insulin c gi vng bi nhiu lin kt mui, lin kt hydro v lin kt cu disulphate gia chui A v chui B. Insulin c tc dng r nht trong tt c cc hormon ca tuyn tu, c bit i vi qu trnh chuyn ho glucid, n c tc dng h ng huyt. Insulin cn kch thch qu trnh tng hp v c ch qu trnh thoi ho glycogen c, gan v m m. c bit, insulin tng cng tng hp acid bo, protein v kch thch s ng phn. Tc dng quan trng nht ca insulin l kch thch s thm nhp glucose, mt s ose, amino acid trogn t bo c v m. Do vy insulin lm gim lng glucose trong mu. Ngoi ra insulin cng lm gim s tn to glucose do lm gim nng enzyme nh pyruvat carboxylase v fructose 1-6 diphosphatase.

Hnh 3.16. Cc amino acid ca chui A v B insulin b

643.2.3.4. Oxytocin, Vasopressin Vasotocin Oxytocin l mt peptide c 9 amino acid. ng vt c v, oxytocin ch khc s thay i ca 2 amino acid l: amino acid v tr th ba l isoleucine v amino acid v tr th tm l leucine (bng 3.3). Vasopressin ca loi ch nhi c cu trc trung gian gia vasopresin v oxytocin ca ng vt c v (amino acid th ba l isoleucin v amino acid th tm l arginine v c tn l vasotocin). Vasopressin l mt peptide c cu trc gm 9 amino acid. .Bng 3.3. So snh cu trc ho hc gia oxytocin v vasopressin ca mt s loi ng vt VaLysine Vasopressin 1 2 3 4 5 6 7 8 9 Cys-Tyr-Phe-Glu-Asn-Cys-Pro-Lys-Gly-NH2 Ln, H m Phn ln ng vt c v

So2 3 4 5 6 7 8 9 Arginine 1 vasopressin Cys-Tyr-Phe-Glu-Asn-Cys-Pro-Arg-Gly-NH2 pres1 2 3 4 5 6 7 8 9 Cys-Tyr-Ile-Glu-Asn-Cys-Pro-Arg-Gly-NH2 1 2 3 4 5 6 7 8 9 Cys-Tyr-Ile-Glu-Asn-Cys-Pro-Leu-Gly-NH2

sin

Vasotocin

ng vt c xng sng, khng c v ng vt c xng sng c v, chim

Oxytocin

Phn ln ng vt c v amino acid th 8 ca vasopressin l arginine (arg-vasopressin), tr ln v h m, amino acid th 8 l lysine (lysvasopressin). Oxytocin c tc dng trn c trn ca t cung v tuyn v, gy co khi t cung sinh con v kch thch s tit sa khi cho con b. Vasopressin c tc dng chng li niu, tng cng ti hp thu nc thn, ng thi lm co mch, do c tc dng tng huyt p.

3.3. Protein3.3.1. Cu trc phn t bc 1, 2, 3, 4 V mt cu trc ngi ta phn bit protein gm bn bc: bc I, bc II, bc III v bc IV (Hinh. 3.17)

65Bc I Bc II Bc III Bc IV

Hnh 3.17. S cc bc cu trc ca protein

3.3.1.1. Cu trc bc I Cu trc bc I biu th trnh t cc gc amino acid trong chui polypeptide, cu trc ny c gi vng bng lin kt peptide (lin kt cng ha tr). Cu trc bc I l phin bn ca m di truyn, vic xc nh c cu trc bc I l c s tng hp nhn to protein bng phng php ho hc hoc bng k thut ca cng ngh sinh hc. Hin nay nhiu loi protein bit c trnh t cc amino acid trong chui polypeptide nh: ribonuclease l mt protein c 124 amino acid c ni vi nhau thnh mt chui, c 4 cu disulfua (hnh 3.18); hemoglobin l protein c 4 chui polypeptide, 2 chui ( mi chui 141 amino acid) v 2 chui (mi chui 146 amino acid); trypsinogen b (229 amino acid); kimotrypsin b (229 amino acid); alcol dehydrogenase nga (374 amino acid); glutamate dehydrogenase b (500 amino acid) v.v..

66

Hnh 3.18. Cu trc bc nht ca ribonuclesae ca b

3.3.1.2. Cu trc bc II Biu th s xon ca chui polypeptide, l tng tc khng gian gia cc gc amino acid gn nhau trong mch polypeptide.

Xon

Lin kt hydrogen Xon Hnh 3.19. Cc kiu xun trong cu trc bc II ca protein

Ni cch khc, cu trc bc II l dng khng gian cc b ca tng phn trong mch polypeptide. Cu trc ny c lm bn nh cc lin kt

67hydrogen c to thnh gia lin kt peptide k gn nhau, cch nhau nhng khong xc nh. Theo Pauling v Cori (1951) cu trc bc II ca protein bao gm 2 kiu chnh l xon v phin gp . trong tc ngi ta tm thy keratin l loi protein c hai dng cu trc: dng bnh thng v dng dui thng.; cu trc phin gp tm thy trong fibroin ca t. Cu trc xun hin nay c tm thy trong nhiu loi protein khc nhau Mt khc t l % xon trong cc protein khc nhau cng thay i kh nhiu. V d trong hemoglobin v mioglobin l 75%; lysosyme l 35%; ribonuclease l 17% ..Bng 3.4. S lng xon v phin gp trong chui n mt s protein S gc (%) Protein (s gc) Chymotrypsin (247) Ribonuclease (124) Carboxypeptidase (397) Cytochrom C (104) Lysosyme (129) Myoglobin (153) Xon 14 26 38 39 40 78 Phin gp 45 35 17 0 12 0

Ngoi ra cn c kiu xon collagen c tm thy trong phn t collagen (hnh 3.20).

Hnh 3.20. Cu trc kiu xun collagen

68n v cu trc ca n l tropocollagen bao gm 3 mch polypeptide bn vo nhau thnh mt dy cp siu xon (v mi mch n c cu trc xon, chiu cao ca mi gc xon trn trc siu xon ny l 2,9 anstron, mt vng xon l 3,3 gc amino acid. Ba chui polypeptide trong dy cp ni vi nhau bng cc lin kt hydrogen. 3.3.1.3. Cu trc bc III Biu th s xon v cun khc ca chui polypeptide thnh khi, c trng cho potein cu, l tng tc khng gian gia cc gc amino acid xa nhau trong chui polypeptide. Trong nhiu protein hnh cu c cha cc gc Cys to nn lin kt disulfua gia cc gc Cys xa nhau trong chui polypeptide lm cho chui b cun li (xem myoglobin hnh 3.21). Ngoi ra cu trc bc III cn c gi vng bng cc loi lin kt khc nh Van der Waals, lin kt hydrogen, lin kt tnh in gia cc gc amino acid v.v... 3.3.1.4. Cu trc bc IV Biu th s kt hp ca cc chui c cu trc bc III trong phn t protein. Hay ni cch khc, nhng phn t protein c cu trc t 2 hay nhiu chui protein hnh cu, tng tc vi nhau trong khng gian to nn cu trc bc IV. Mi mt chui polypeptide c gi l mt tiu n v (subunit), chng gn vi nhau nh cc lin kt hydrogen, tng tc Van der Waals gia cc nhm phn b trn b mt ca cc tiu n v lm bn cu trc bc IV.

Myoglobin

Hemoglobin

Hnh 3.21. Cu trc bc III ca myoglobin v bc IV ca hemoglobin

(hemoglobin l protein c 4 chui polypeptide2 chui v 2 chui ; myoglobin ch gm mt chui polypeptide)

693.3.2. Mt vi tnh cht ca protein 3.3.2.1. Tnh cht l-ho ca protein - Tnh tan ca protein Cc loi protein khc nhau c kh nng ho tan d dng trong mt s loi dung mi nht nh, chng hn nh albumin d tan trong nc; globulin d tan trong mui long; prolamin tan trong ethanol, glutelin ch tan trong dung dch kim hoc acid long v.v... - Tnh ngm nc ca protein Trong mi trng nc, protein kt hp vi nc trng ln tr thnh dng keo, hay ni cch khc protein trng thi hydrate ho, cc phn t nc bm vo cc nhm a nc trong phn t protein nh -NH2, -COOH..., lp o nc bao quanh phn t protein l mt trong cc yu t lm bn vng cu trc, ngn cch cc phn t protein khng cho chng dnh vo nhau thnh ta. - nht ca dung dch protein Khi protein ho tan trong dung dch, mi loi dung dch ca nhng protein khc nhau c nht khc nhau (bng 3.5). Ngi ta c th li dng tnh cht ny xc nh khi lng phn t ca protein ( nht cng cao th khi lng phn t cng cao).Bng 3.5. nht ca mt s protein Protein Gelatin Albumin trng Gelatin Albumin trng Nng % (trong nc) 3,0 3,0 8,0 8,0 nht tng i (ca nc =1) 4,54 1,20 14,2 1,57

- Hng s in mi ca dung dch protein Khi thm cc dung mi hu c trung tnh nh ethanol, aceton vo dung dch protein trong nc th tan ca protein gim v protein s kt ta do vic gim mc hydrate ho ca cc nhm ion ho ca protein, lp o mt nc, cc phn t protein kt hp vi nhau thnh ta. Nh vy, hng s in mi ca dung mi lm ngn cn lc tnh in gia cc nhm tch in ca protein v nc. Mi lin h c c trng bi biu thc:

70L1 - l2 F= D - hng s in mi ca dung dch F- lc tnh in gia cc ion tch in L1 , l2 - in tch cc ion, r - khong cch gia cc ion - Tnh cht in li ca protein Cng nh cc amino acid, protein l cht in li lng tnh v trong phn t protein c nhiu nhm phn cc mnh (bn gc R) ca amino acid v d: nhm COOH th hai ca Asp, Glu; nhm NH2 ca Lys; nhm OH ca Ser, Thr, Tyr v.v...Trng thi tch in ca cc nhm ny ph thuc vo pH ca mi trng. mt pH no m tng in tch (+) v in tch (-) ca phn t protein bng khng, phn t protein khng di chuyn trong in trng gi l pHi (isoelectric - im ng in) ca protein. Nh vy protein cha nhiu Asp, Glu (amino acid c tnh acid mnh) th pHi trong vng acid, ngc li nhiu amino acid kim nh Lys, Arg, His th pHi trong vng kim. mi trng c pH < pHi , protein a s l mt cation, s in tch dng ln hn s in tch m. pH > pHi phn t protein th hin tnh acid, cho ion H+, do s in tch m ln hn s in tch dng, protein l mt a anion, tch in m.Bng 3.5. Gi tr pHi ca mt s protein Protein Pepsin Albumin trng Casein Albumin huyt thanh Gelatin pHi 1,0 4,6 4,7 4,9 4,9 Protein Globulin sa Hemoglobin Ribonuclease Trypsin Cytochrom C Prolamin pHi 5,2 6,8 7,8 10,5 10,6 12,0

Dr2 Trong :

Trong mi trng c pH = pHi ca protein, protein d dng kt t li vi nhau v th ngi ta li dng tnh cht ny xc nh pHi ca protein cng nh kt ta protein. Mt khc do s sai khc nhau v pHi gia cc protein m c th iu chnh pH ca mi trng tch ring cc protein ra khi hn hp ca chng.

71- S kt ta bng mui ca dung dch protein Mui trung tnh c nh hng r ti ho tan ca protein hnh cu: vi nng thp chng lm ho tan nhiu protein. Tc dng khng ph thuc vo bn cht ca mui trung tnh, m ph thuc vo nng mui v s in tch ca mi ion trong dung dch, tc l ph thuc vo lc ion ca dung dch ( = 1/2 C1 Z1, 2 trong l k hiu ca tng, C1 l nng ca mi ion, Z1 l in tch ca mi ion). Cc mui c ion ho tr 2 (MgCl2, MgSO4...) lm tng ng k tan ca protein hn cc mui c ion ho tr 1 (NaCl, NH4Cl, KCl...). Khi tng ng k nng mui trung tnh th tan ca protein bt u gim v nng mui rt cao, protein c th b kt ta hon ton. Cc protein khc nhau b kt ta nhng nng mui trung tnh khc nhau. Ngi ta s dng tnh cht ny chit xut v tch ring protein khi hn hp. l phng php dim tch (kt ta protein bng mui). Th d dng mui amonium sulfate 50% bo ho kt ta globulin v dung dch amonium sulfate bo ho kt ta albumin t huyt thanh. - Biu hin quang hc ca protein Cng nh nhiu cht ho hc khc, protein c kh nng hp th v bc x nh sng di dng lng t h. V vy c th o cng hp th ca protein trong dung dch hay cn gi l mt quang thng k hiu bng ch OD (Optical Density). Da trn tnh cht ngi ta sn xut ra cc loi my quang ph hp th phn tch protein. Nhn chung protein u c kh nng hp th nh sng trong vng kh kin (t 350nm- 800nm) v vng t ngoi (t 320nm xung ti 180nm). Trong vng nh sng kh kin protein kt hp vi thuc th hp th mnh nht vng nh sng 750nm (nh lng protein theo Lowry). i vi vng t ngoi dung dch protein c kh nng hp th nh sng t ngoi hai vng bc sng khc nhau: 180nm-220nm v 250nm - 300nm. bc sng t 180nm-220nm l vng hp th ca lin kt peptide trong protein, cc i hp th 190nm. Do lin kt peptide c nhiu trong phn t protein nn hp th kh cao, cho php nh lng tt c cc loi protein vi nng thp. Tuy nhin vng hp th ny ca cc lin kt peptide trong protein c th b dch v pha c bc sng di hn khi c mt s tp cht ln trong dung dch protein. Mt khc chnh cc tp cht ny cng hp th nh sng t ngoi vng bc sng 180nm-220nm. V th trong thc t thng o hp th ca dung dch protein bc sng 220nm-240nm. bc sng t 250nm-300nm l vng hp th cc amino acid thm (Phe, Tyr, Trp) c trongphn t protein hp th cc i 280nm. C th s dng phng php o hp th ca dung dch protein bc sng 280nm

72 nh tnh v nh lng cc protein c cha cc amino acid thm. Hm lng cc amino acid thm trong cc protein khc nhau thay i kh nhiu, do dung dch ca cc protein khc nhau c nng ging nhau c th khc nhau v hp th bc sng 280nm. Ngoi ra c nhiu cht khc trong dung dch cng c nh hng n hp th protein. V vy, cc phng php o hp th vng nh sng t ngoi thng c dung nh lng protein c tinh sch hoc xc nh protein trong cc phn on nhn c khi sc k tch cc protein qua ct. - Kt ta thun nghch v khng thun nghch protein Khi protein b kt ta n thun bng dung dch mui trung tnh c nng khc nhau hoc bng alcohol, acetone nhit thp th protein vn gi nguyn c mi tnh cht ca n k c tnh cht sinh hc v c th ho tan tr li gi l kt ta thun nghch. Cc yu t kt ta thun nghch c dng thu nhn ch phm protein. Trong qu trnh kt ta thun nghch mui trung tnh va lm trung ho in va loi b lp v hydrate ho ca protein, cn dung mi hu c vn ho nc s ph hy lp v hydrate nhanh chng. Trong ch phm protein nhn c cn ln cc cht dng kt ta, cn s dng phng php thch hp loi b cc cht ny. V d c th dng phng php thm tch loi b mui. Ngc li kt ta khng thun nghch l protein sau khi b kt ta khng th phc hi li trng thi ban u. S kt ta ny thng c s dng loi b protein ra khi dung dch, lm ngng phn ng ca enzyme. Mt trong nhng yu t gy kt ta khng thun nghch n gin nht l un si dung dch protein (s ni k hn trong phn bin tnh protein sau). - Cc phn ng ho hc ca protein Cng nh cc amino acid v peptide, protein c cc phn ng ho hc tng t, l: phn ng ca cc nhm -COOH, -NH2, gc R v phn ng to mu c trng ca lin kt peptide nh phn ng biure (xem chng 2 v 3. y xin c gii thiu thm mt s phn ng mu c trng khc, c ngha quan trng trong pht hin protein v cc gc amio acid trong chui polypeptide. + Phn ng vi thuc th Folin-Ciocateau Thuc th Folin-Ciocateau c cha phosphomolipdic acid v phosphovolframic acid cc cht ny lm tng nhy ca phn ng biure, mt khc phn ng vi gc Tyr v Trp trong phn t protein. Cc gc amino acid ny tham gia trong qu trnh to phc cht mu xanh da tri. + Cc phn ng mu c trng khc ca protein

73Nhng phn ng ny c c l do s c mt ca cc nhm nh chc ha hc xc nh trong phn t protein. C th s dng chng pht hin amino acid, protein trong dung dch. Phn ng xanthproteic: cc gc amino acid Tyr, Trp, Phe trong protein tc dng vi HNO3 c to thnh mu vng v sau khi thm kim s chuyn thnh da cam. Phn ng Pauli: cc gc Tyr, His trong protein tc dng vi diazobenzosulfonic acid to thnh mu anh o. Phn ng Millon: gc Tyr tc dng vi thu ngn nitrate trong HNO3 c to thnh kt ta mu nu t. Phn ng Saccaguichi: gc Arg tc dng vi dung dch kim ca -naphtolv hypobromitecho mu anh o. Phn ng Adamkievich: gc Trp tc dng vi glyoxylic acid v H2SO4 c to thnh vng tm mt phn cch. 3.3.2.2. Tnh cht v chc nng sinh hc ca protein Protein l hp cht hu c c ngha quan trng bc nht trong c th sng, v mt s lng, n chim khng di 50% trng lng kh ca t bo. T lu, bit rng protein tham gia mi hot ng sng trong c th sinh vt, ngoi vai tr l thnh phn chnh trong cu trc ca t bo v m, protein cn c nhiu chc nng phong ph khc quyt nh nhng c im c bn ca s sng nh s truyn t thng tin di truyn, s chuyn ho cc cht do cc enzyme, cc khng th chng li bnh tt, cc hormon dn truyn cc tn hiu trong t bo v.v... u c bn cht l cc protein. Trong c th protein c mt s vai tr sau y: - Chc nng to hnh Ngoi cc protein lm nhim v cu trc nh v virus, mng t bo, cn gp nhng protein thng c dng si nh: sclerotin c trong lp v ngoi ca su b; fibroin ca t tm, nhn; collagen, elastin ca m lin kt, m xng. Collagen m bo cho bn v tnh mm do ca m lin kt. - Chc nng xc tc Hu ht cc phn ng xy ra trong c th u do cc protein c bit ng vai tr xc tc, nhng protein c gi l cc enzyme. Mc d gn y ngi ta pht hin c mt loi RNA c kh nng xc tc qu trnh chuyn ho tin RNA thng tin (pre-mRNA) thnh RNA thng tin (mRNA), ngha l enzyme khng nht thit phi l protein. Nhng nh ngha c tnh cht kinh in: enzyme l nhng protein c kh nng xc tc

74c hiu cho cc phn ng ho hc, l cht xc tc sinh hc vn c ngha c bit quan trng. Hin nay ngi ta bit c khong 3.500 enzyme khc nhau, nhiu enzyme c tinh sch, kt tinh v nghin cu cu trc. - Chc nng bo v Ngoi vai tr l thnh phn chnh trong xc tc, cu trc ca t bo v m, protein cn c chc nng chng li bnh tt bo v c th. l cc protein tham gia vo h thng min dch, c bit nhiu loi protein thc hin cc chc nng ring bit to nn hiu qu min dch c hiu v khng c hiu. Cc protein min dch c nhc n nhiu hn c l cc khng th, b th v cc cytokine. Ngoi ra protein cn tham gia vo qu trnh ng mu chng mt mu cho c th hoc mt s loi c th sn xut ra nhng c t c bn cht l protein nh enzyme nc rn, lectin v.v...,c kh nng tiu dit k th bo v c th. - Chc nng vn chuyn Trong c th c nhng protein lm nhim v vn chuyn nh hemoglobin, mioglobin, hemocyanin vn chuyn O2, CO2 v H+ i khp cc m, cc c quan trong c th. Ngoi ra cn c nhiu protein khc nh lipoprotein vn chuyn lipid, ceruloplasmin vn chuyn ng (Cu) trong mu v.v...Mt trong nhng protein lm nhim v vn chuyn c nhc n nhiu nht l hemoglobin. - Chc nng vn ng. Nhiu protein lm nhim v vn ng co rt nh myosin, actin si c, chuyn v tr ca nhim sc th trong qu trnh phn bo v.v... -Chc nng d tr v dinh dng Cc protein lm nhim v d tr nh casein ca sa, ovalbumin ca trng, feritin ca lch (d tr st) v.v...Protein d tr ny chnh l ngun cung cp dinh dng quan trng cho cc t chc m, phi pht trin. - Chc nng dn truyn tn hiu thn kinh Nhiu loi protein tham gia vo vic dn truyn tn hiu thn kinh i vi cc kch thch c hiu nh: sc t th gic rodopsin mng li mt. - Chc nng iu ho Cc protein lm nhim v iu ho qu trnh trao i cht thng qua tc ng ln b my thng tin di truyn nh cc hormon, cc protein c ch c hiu enzyme u c chc nng iu ho nhiu qu trnh trao i cht, chng hn cc protein repressor vi khun c th lm ngng qu trnh sinh tng hp enzyme t cc gen tng ng.

75- Chc nng cung cp nng lng Protein cng l ngun cung cp nng lng quan trng cho mi hot ng sng trong c th. Trong c th cc protein b phn gii thnh cc amino acid, t tip tc to thnh hng lot cc sn phm, trong c cc ceto acid, aldehyde v carboxylic acid. Cc cht ny u b oxy ho dn dn to thnh CO2 v H2O ng thi gii phng ra nng lng. 3.3.3. Phn loi protein Protein l hp cht a dng v thnh phn cu trc, chc nng; khi lng phn t ca chng cng rt khc nhau (bng 3.6). Do s phn loi protein c th da vo nhng mc ch khc nhau. C hai cch phn loi thng thng nht: 3.3.3.1. Phn loi theo hnh dng - Protein dng si C hnh dng di, thng l hnh si, chiu di ca phn t protein si ln hn ng knh ca n hng trm ln. Protein si tng i bn vng, khng tan trong nc v dung dch mui long, cc chui polypeptide ca protein si nm dc theo mt trc thnh nhng si di. Protein si l yu t cu trc c bn ca m lin kt ng vt cao cp, th d collagen gn v m xng,elastin m lin kt n hi, -keratin tc da v.v... - Protein dng cu C dng gn nh hnh cu hoc hinh bu dc, chiu di ca phn t protein cu c th ln hn ung knh ca n t 3 n 10 ln. Protein cu khng bn vng bng protein si, a s tan trong dung dch nc v d khuych tn, thng c chc nng hot ng sng ca t bo nh cc enzyme, cc hormon, cc protein vn chuyn nh albumin huyt thanh, hemoglobin v.v... - Protein dng trung gian Mt s protein dng trung gian, va c c im ca protein si, va c c im ca protein cu. Th d myosin (yu t cu trc v chc nng quan trong ca c) c cu trc hnh que di l c im ca protein si, nhng li tan trong dung dch mui l c im ca protein cu. Ngoi ra, trong nhm trung gian ny cn c cht tin thn ca fibrin l fibrinogen. 3.3.3.2. Phn loi theo thnh phn ho hc Protein gm hng trm, hng ngn, thm ch hng vn amino acid ni vi nhau bng lin kt peptide to nn mt hay nhiu chui polypeptide c cu trc rt phc tp.

76Cn c s c hay vng mt ca mt s thnh phn c bn cht khng phi protein m ngi ta chia protein thnh hai nhm:Bng: 3.6 Khi lng (MW) v cu trc phn t ca mt s protein Protein Glucagon Insulin Ribonuclease (ty b) Lysozyme (lng trng trng) Myoglobin (tim nga) Chymotripsin (ty b) Hemoglobin (ngi) Albumin (huyt thanh ngi) Hexokinase (men bia) Tryptophan-synthetase (E.coli) -globulin (nga) Glycogen-phosphorylase (c th) Glutamate-dehydrogenase (gan b) Synthetase ca acid bo (men bia) Virus khm thuc l Khi lng (Dalton) 3482 5733 12.640 13.930 16.890 22.600 64.500 68.500 96.000 117.000 149.000 495.000 1.000.000 2.300.000 40.000.000 S gc amino acid 29 51 124 129 153 241 574 550 800 975 1.250 4.100 8.300 20.000 336.500 S chui polypeptide 1 2 1 1 1 3 4 1 4 4 4 4 40 21 2.130

- Protein n gin Protein n gin l nhng protein m phn t ca chng gm ton amino acid. Th d mt s enzyme ca tu b nh ribonuclease gm ton amino acid ni vi nhau thnh mt chui polypeptide duy nht (c 124 gc amino acid, khi lng phn t 12.640), chymotrypsin gm ton amino acid ni vi nhau thnh ba chui polypeptide (c 241 gc amino acid, khi lng phn t 22.600) v.v...Da theo kh nng ho tan trong nc hoc trong dung dch ngi ta c th chia cc protein n gin ra mt s nhm nh nh: - Albumin: tan trong nc, b kt ta nng mui (NH4)2SO4 kh cao (70-100%). - Globulin: khng tan hoc tan t trong nc, tan trong dung dch long ca mt s mui trung tnh nh NaCl, KCl, Na2SO4..., v b kt ta nng mui (NH4)2SO4 bn bo ho. - Prolamin: khng tan trong nc hoc dung dch mui long, tan trong ethanol, isopropanol 70-80%.

77- Glutein: ch tan trong dung dch kim hoc acid long. - Histon: l protein c tnh kim d tan trong nc, khng tan trong dung dch amoniac long. - Protein phc tp Protein phc tp l nhng protein m phn t ca chng ngoi cc amino acid nh protein n gin cn c thm thnh phn khc c bn cht khng phi l protein cn gi l nhm thm (nhm ngoi). Tu thuc vo bn cht ca nhm ngoi m ngi ta chia cc protein phc tp ra cc nhm nh v thng gi tn cc protein bt u bng tip u ng ch bn cht nhm ngoi: - Lipoprotein: nhm ngoi l lipid. - Nucleoprotein: nhm ngoi l nucleic acid. - Glucoprotein: nhm ngoi l carbohydrate v dn xut ca n. - Phosphoprotein: nhm ngoi l phosphoric acid. - Chromoprotein: nhm ngoi l hp cht c mu. Tu theo tnh cht ca tng nhm ngoi m c nhng mu sc khc nhau nh ( hemoglobin), vng ( flavoprotein)...

78

TI LIU THAM KHOTi liu ting Vit1. Trn Th n, i Duy Ban, Nguyn Hu Chn, nh H, L c Trnh. 1980. Ho sinh hc. NXB Y hc, H Ni 2.Phm Th Trn Chu, Trn Th ng. 1999. Ho sinh hc. NXB Gio dc, H Ni. 3. Nguyn Ln Dng, Phm Vn Ty, Nguyn nh Quyn. 1999. Vi sinh vt hc. NXB Gio dc,H Ni. 4. L c Trnh. 1998. Hormon. NXB Y hc. H ni

Ti liu ting Anh1. Dennison C. 2002. A Guide To Protein Isolation. Kluwer Academic Publishers. New York, Boston, Dordrecht, Lodon, Moscow. 2. Fersht A., 1998, Structure and Mechanism in Protein Science, W. H. Freeman, 3rd Rev Edit. 3. Lehninger A. L. 2004. Principle of Biochemistry, 4th Edition. W.H Freeman, 2004 4. Liebler D. C. 2002. Introduction to proteomics. Humana Press Inc. Totuwa, New Jersey. 5. Lodish H, 2003. Molecular Cell Biology. 5th ed, W.H Freeman, 2003 6. Walker J. M. 1996. The Protein Protocols Hand book. 2nd ed. Humana Press Inc. Totuwa, New Jersey.

79

Chng 4

Nucleic acid4.1. Thnh phn ho hc ca nucleic acidNucleic acid, vt cht mang thng tin di truyn ca cc h thng sng, l mt polymer c hnh thnh t cc monomer l nucleotide. Trong nucleic acid c cha cc nguyn t C, H, O, N v P. Hm lng P t 8- 10% Mi nucleotide gm 3 thnh phn kt hp vi nhau theo t l 1:1:1, bao gm: nhm phosphate, ng pentose (l ng 5 carbon) v mt base nit (nitrogen). 4.1.1 Base nit (Nitrogen) Cc base nit (nitrogen) thuc phn t nucleic acid u l dn xut ca base purine hoc pyrimidine. Cc base purine gm adenine (6-amino purine) v guanine (2-amino, 6-aminopurine), cc base nit pyrimidine gm thymine (2,6-dioxy, 5-methylpyrimidine), cytosine(2-oxy,6aminopyrimidine) v uracil (2,6 dioxypyrimidine).( Hnh 4.1.)

Hnh 4.1 Cng thc cu to ca cc base nit (nitrogen) trong nucleic acid

4.1.2 ng pentoseng pentose trong nucleic acid gm c hai loi l ng deoxyribose v ribose. S c mt ca 2 loi ng ny l mt trong nhng c im phn bit DNA v RNA. 4.1.3 Phosphoric acid L mt acid v c - H3PO4

80

Hnh 4. 2. Cng thc cu to ca hai loi ng pentose trong nucleic acid

4.1.4. S to thnh nucleoside Nucleoside l sn phm thu phn khng hon ton ca nucleic acid. Nucleoside gm c hai thnh phn l ng pentose v mt base nit (nitrogen, thuc purine hay pyrimidine).

81

Hnh 4. 3. Cu to ho hc ca cc nucleoside v nucleotide

4.1.5. S to thnh nucleotide Nucleotide cng l sn phm thu phn khng hon ton ca nucleic acid. Nucleotide gm c ba thnh phn: ng pentose, mt base nit (nitrogen) v phosphoric acid (Hnh 4.3). 4.1.6. S to thnh nucleic acid Cc nucleotide c ni vi nhau bng lin kt phosphodiester Acide thng qua cc nhm OH v tr C3 v C5 ca ng pentose to thnh mt chui di gi l polynucleotide. Do lin kt phosphodiester c tao thnh v tr C3 v C5 nn chui polypeptide c tnh phn cc: u 5 thng c gc phosphate v u 3 thng c OH t do. Nucleic acid gm hai loi phn t c cu to rt ging nhau l DNA (desoxyribonucleic acid) v RNA (ribonucleic acid). 4.1.7. Mt s nucleotide quan trng khng tham gia cu to nucleic acid - ADP v ATP

82ADP (adenosindiphosphate) v ATP (adenosintriphosphate) l nhng dn xut ca adenine, chng tham gia qu trnh phosphoryl ho-oxy ho. ATP c coi l ngun phosphate cao nng trong t bo (Hnh 4.4).

Hnh 4.4. Cu to ho hc ca ADP v ATP

- cAMP(AMP vng) Adenosinemonophosphate vng c hnh thnh t ATP, cAMP ch tm thy t bo ng vt v vi khun, n thng lin kt vi mng bo tng ca t bo v tham gia nhiu qu trnh chuyn ho. cAMP c th c sinh ra nh mt s hormone hot ho adenylcyclase (Hnh 4.5.) - UDP v UTP UDP (uridinediphosphate) v UTP (uridinetriphosphate) u l nhng dn xut ca uracil l nhng coenzyme quan trng trong cc phn ng trung gian chuyn ho glucose v galactose. Ngoi ra, chng cn tham gia trong vic hnh thnh nhng hp cht phosphate giu nng lng.

Hnh 4.5. Cu to ho hc ca AMP vng (cAMP)

- CDP v CTP CDP (cytidindiphosphate) v CTP (cytidinetriphosphate) l nhng dn xut ca cytidine. CTP cng l hp cht giu nng lng v co th tham gia nhiu phn ng khc nhau nh: phosphoryl ho ethanolamine

83dn n s sinh tng hp cephaline hoc phn ng vi phosphate choline hnh thnh cytidinediphosphate-choline (CDP-Choline, hnh 4.6).

Hnh 4.6. Cu to ho hc ca CDP- cholin

4.1.8. Cc coenzyme nucleotide Hin nay ngi ta bit c mt s nucleotide tham gia cu to nn cc coenzyme quan trng nh vitamin B5 (pantothenic acid) trong coezyme A (SH-CoA), vitamin B2 (riboflavine) trong coenzyme flavin adenine inucleotide (FAD) v vitamin PP (nicotinamide) trong coenzyme nicotinamide adenine dinucleotide (NAD) v.v...Chng c phosphoryl ho khi lm chc phn nhm ngoi ca cc enzyme trong chuyn ho trung gian, (hnh 4.7)

84

FAD

Hnh 4.7. Cu to ho hc ca mt s coenzyme

4.2. Cu trc ca nucleic acid4.2.1 DNA (Desoxyribonucleic acid) Phn t DNA l mt chui xon kp gm hai chui n. Mi chui n l mt chui nucleotide. Mi nucleotide gm ba thnh phn: nhm phosphate, ng desoxyribose v mt trong bn base v thng c k hiu bng ch ci u tin ca cc base (A-adenine, C- cytosine, Gguanine v T- thymine). Hai chui n kt hp vi nhau nh cc lin kt hydrogen hnh thnh gia cc base b sung nm trn hai chui: A b sung cho T v C b sung cho G. Mi chui n c mt trnh t nh hng vi mt u 5phosphate t do, u kia l 3 hydroxyl t do (quy c l 5 3. Hng ca hai chui n trong chui xon kp ngc nhau, nn c gi l hai chui i song. Nhng phn tch cu trc hin i cho thy

85cu trc ca DNA khng phi lun lun tng ng vi dng c gi l B m Watson v Crick a ra. Do s tc ng ca cc hp cht c trng lng nh hoc protein dng B c th chuyn sang dng A (nn nhiu hn) hoc l dng Z (xon tri). Chng c th t gp li (DNA) hoc xon mnh, v d mt chui kp DNA c di l 20 cm c nn trong mt chromosome c kch thc l 5 m.Lin kt hydrogen

1 nm

3,4 nm

0,34 nm (a) Cu trc ca DNA (b) Cu trc ha hc ca mt phn DNA

Hnh 4.8. Chui xon kp ca DNA

Phn t DNA trong nhim sc th ca sinh vt eukaryote dng thng, cn phn ln t bo prokaryote (vi khun) phn t DNA c dng vng. D dng no th cc phn t DNA u tn ti di dng cun cht. Trong t bo eukaryote, DNA kt hp cht ch vi cc protein l histone.

86Trc ng-phosphate Cc base

Thymine (T)

Adenine (A)

Cytosine (C)

DNA nucleotide Phosphate ng (deoxyribose)

.

Guanine (G)

Hnh 4.9. Cu trc ca cc nucleotide in hnh.

DNA ca eukaryote c kch thc rt ln (v d DNA ngi c th di n 1 m) nn cu hi t ra l phn t ny phi c nn nh th no vo th tch rt hn ch ca nhn. Vic nn c thc hin nhiu mc , mc thp nht l nucleosome v mc cao nht l cu trc nhim o sc cht. Tht vy, ng knh ca chui xon DNA ch l 20 A , trong khi si nhim sc cht quan st di knh hin vi in t c ng knh o o 100 A , i khi t 300 A . iu ny chng t phn t DNA tham gia hnh o thnh nhng cu trc phc tp hn (Hnh 4.10). Si c ng knh 100 A l mt chui nhiu nucleosome. l nhng cu trc hnh thnh t mt

87o

chui DNA qun quanh mt li gm 8 phn t histon. Si 100 A ny o c t chc thnh cu trc phc tp hn l si c ng knh 300 A . Trong nhn t bo, cc si va k trn kt hp cht ch vi nhiu protein khc nhau v c vi cc RNA to hnh nhim sc cht, mc t chc cao nht ca DNAChui xon kp DNA

2 nm

Dng xu chui ca nhim sc th

11 nm

Si nhim sc cht ng knh 30 nm gm cc nucleosome c ng gi

30 nm

Vng nhim sc th dng lng lo

300 nm

Vng nn cht ca nhim sc th trung k

700 nm

Nhim sc th trung k

1400 nm

Hnh 4.10. Cu trc nucleosome v nhim sc th.

Phn t DNA c sp xp trn nhim sc th lm cho chiu di ngn li hn 50.000 ln. Cc DNA eukaryote c c im khc vi DNA prokaryote. Ton b phn t DNA prokaryote u mang thng tin m ha cho cc protein trong khi DNA eukaryote bao gm nhng trnh t m ho (cc exon)

88xen k vi nhng trnh t khng m ho (intron). Cc trnh t m ho eukaryote chm ngp trong mt khi ln DNA m cho n nay vn cha r tc dng. Ty theo mc hin din ca chng trong nhn, cc trnh t DNA c chia lm ba loi: - Cc trnh t lp li nhiu ln. V d: ng vt c v cc trnh t ny chim 10-15% genome (h gen). l nhng trnh t DNA ngn (10200 kb), khng m ho, thng tp trung nhng vng chuyn bit trn nhim sc th nh vng tm ng (trnh t CEN) hay u cc nhim sc th (trnh t TEL). Chc nng ca cc trnh t ny cha r, c th chng tham gia vo qu trnh di chuyn DNA trn thoi v sc (trnh t CEN) hoc vo qu trnh sao chp ton vn ca phn DNA nm u mt nhim sc th (trnh t TEL). - Cc trnh t c s ln lp li trung bnh. V d: genome ngi cc trnh t ny chim 25-40 %. Chng a dng hn v c kch thc ln hn (100-1.000 kb) cc trnh t lp li nhiu ln. Cc trnh t ny phn b trn ton b b gen. Chng c th l nhng trnh t khng m ha m cng c th l nhng trnh t m ha cho rRNA, tRNA v RNA 5S. - Cc trnh t duy nht: l cc gen m ha cho cc protein, c trnh t c trng cho tng gen. Mt c im ca phn t DNA c ngha rt quan trng c s dng vo phng php lai phn t. l kh nng bin tnh v hi tnh. Bin tnh l hin tng hai si n ca phn t DNA tch ri nhau khi cc lin kt hydrogen gia cc base b sung nm trn hai si b t do cc tc nhn ha hc (dung dch kim, formamide, urea) hay do tc nhn vt l (nhit). Sau , nu iu chnh nhit v nng mui thch hp, cc si n c th bt cp tr li theo nguyn tc b sung, hnh thnh phn t DNA ban u, l s hi tnh. 4.2.2 RNA (Ribonucleic acid ) Phn t RNA c cu to tng t DNA vi ba im khc bit sau: - Phn t RNA l chui n. - ng pentose ca phn t DNA l deoxyribose c thay bng ribose. - Thymine, mt trong bn loi base hnh thnh nn phn t DNA, c thay th bng uracil trong phn t RNA. Cu trc v chc nng ca RNA c s bin i r rt. V c bn RNA ch l cht mang thng tin di truyn virus, sau ngi ta chng minh rng n khng nhng ng vai tr c bn vic chuyn thng tin di truyn m cn c vai tr cu trc khi to nn phc h RNA-protein.

89Theo mt l thuyt tin ha m i din l Manfred Eigen, RNA l cht mang thng tin di truyn, thnh vin trung gian ca s biu hin gen, thnh phn cu to v l cht xc tc. Nhm OH ru v tr th hai ca ribose cn thit cho a chc nng lm nhiu lon s to thnh chui kp, qua lm tng khng bn vng ca lin kt photphodieste. Trong t bo c ba loi RNA chnh, c cc chc nng khc nhau: - Cc RNA thng tin (mRNA) mRNA l bn sao ca nhng trnh t nht nh trn phn t DNA, c vai tr trung tm l chuyn thng tin m ha trn phn t DNA n b my gii m thnh phn t protein tng ng. Cc RNA c cu trc a dng, kch thc nh hn so vi DNA v ch cha thng tin m ha cho mt hoc vi protein v ch chim khong 2-5% tng s RNA trong t bo. Qu trnh chuyn thng tin c th hin nh sau: Phin m DNA RNA Dch m Protein

Escherichia coli, kch thc trung bnh ca mt phn t mRNA khong 1,2 kb. - RNA vn chuyn (tRNA) tRNA lm nhim v vn chuyn cc amino acid hot ha n ribosome tng hp protein t cc mRNA tng ng. C t nht mt loi tRNA cho mt loi amino acid. tRNA vn chuyn cha khong 75 nucleotide (c trng lng khong 25 kDa), l phn t RNA nh nht. Cc tRNA c cu trc dng c ba l (Hnh 7). Cu trc ny c n nh nh cc lin kt b sung hin din nhiu vng ca phn t tRNA. Hai v tr khng c lin kt b sung ng vai tr c bit quan trng i vi chc nng ca tRNA: - Trnh t anticodon gm ba nucleotide. - Trnh t CCA, c kh nng lin kt cng ha tr vi mt amino acid c trng. - RNA ribosome (rRNA) rRNA l thnh phn c bn ca ribosome, va ng vai tr xc tc v cu trc trong s tng hp protein. Ty theo h s lng rRNA c chia thnh nhiu loi: eukaryote c rRNA 28S, 18S, 5,8S v 5S, cn cc rRNA E. coli c ba loi: 23S,

9016S v 5S. rRNA chim nhiu nht trong ba loi RNA (80% tng s RNA t bo), tip n l tRNA v mRNA ch chim 5%. Ribosome ca mi t bo u gm mt tiu n v nh v mt tiu n v ln. Mi tiu n v c mang nhiu protein v rRNA c kch thc khc nhau.Amino acid

anticodon

.Hnh 4.11. M hnh cu trc ca mt tRNA

- Mt s loi RNA khc. T bo sinh vt nhn chun cn cha mt s loi RNA khc, chng u c vai tr nht nh trong b my tng hp protein nh: + snRNA (small nuclear) l nhng phn t RNA nh tham gia vo vic ghp ni cc exon. + hn RNA( heterogenous nuclear) l nhng RNA khng ng nht nhn t bo. + scRNA (small cytoplasmic) l nhng RNA nh ca t bo cht.

91Bng 4.1. Cc phn t RNA trong E. coli Loi rRNA Tng s tng i (%) 80 H s lng (S) 23 16 5 4 Khi lng phn t (kDa) 1,2 103 0,55 103 3,6 101 2,5 101 Khng ng nht S lng nucleotide 3700 1700 120 75

tRNA mRNA

15 5

Nhn chung tt c RNA trong t bo u c tng hp nh enzyme RNA polymerase. Enzyme ny i hi nhng thnh phn sau y: a) Mt khun mu, thng l DNA chui i. b) Tin cht hot ha: Bn ribonucleoside triphosphate: ATP, GTP, UTP v CTP. Sinh tng hp RNA ging DNA mt s im, th nht hng tng hp l 5 3, th hai l c ch ko di ging nhau: nhm 3-OH u cui ca chui tng hp l v tr gn kt ca nucleoside triphosphate tip theo. Th ba, s tng hp xy ra do thy phn pyrophosphate. Tuy nhin, khc vi DNA l RNA khng i hi mi (primer). Ngoi ra RNA polymerase khng c hot tnh nuclease sa cha khi cc nucleotide b gn nhm. C ba loi RNA trong t bo c tng hp trong E. coli nh mt loi RNA polymerase. ng vt c v cc RNA khc nhau c tng hp bng cc loi RNA polymerase khc nhau.

4.3. Mt s tnh cht ca nucleic acidDung dch nucleic acid c nht cao, c hot tnh quang hc (lm quay mt phng nh sang phn cc). Nucleic acid hp th mnh vng nh sng t ngoi c bc sng 250-280 nm, cc i hp th 260 nm. Tnh cht ny c s dng dnh lng nucleic acid v xc nh sch ca nucleic acid. Khi un nng dung dch nucleic acid nhit cao, thm acd hoc kim ion ho cc base ca n, nucleic acid b bin tnh. Phn t DNA xon kp b tho ri, hp th bc song 260 nm tng ln. S tng hp th ny gi l hin tng tng sc t (hyperchromism). Nhit lm mt mt na cu trc xon kp cu phn t DNA c gi l nhit

92nng chy (melting temperature) vit tt l Tm. Cc DNA giu cc base G v C c nhit nng chy cao. DNA phn ng vi thuc th fucsin to thnh mu (phn ng Feulgen), phn ng ny thng s dng trong ho t bo. phn bit DNA v RNA ngi ta dng cc phn ng c trng vi thuc th orcine to thnh mu xanh lc bn, desoxyribose ca DNA phn ng vi diphenylamine to thnh mu xanh da tri bn.

TI LIU THAM KHOTi liu ting Vit1. Trn Th n, i Duy Ban, Nguyn Hu Chn, nh H, L c Trnh. 1980. Ho sinh hc. NXB Y hc, H Ni 2. Phm Th Trn Chu, Trn Th ng. 1999. Ho sinh hc. NXB Gio dc, H Ni. 3. H Hunh Thu Dng. 1998. Sinh hc phn t. NXB Gio dc, H Ni. 4. Phm Thnh H. 2001. Di truyn hc, (ti bn ln th 3) NXB Gio dc, H Ni.

Ti liu ting Anh1. Lehninger A.L. , 2004. Principle of Biochemistry , 4th Ed., E-Book 2. Lodish H., 2003. Molecular Cell Biology. 5th Ed. E-book

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Chng 5

VitaminVitamin l mt nhm cht hu c c cc tnh cht l, ho hc rt khc nhau. Tc dng ca chng trn cc c th sinh vt cng rt khc nhau nhng u rt cn thit cho s sng ca sinh vt, nht l i vi ngi v ng vt. Khi thiu mt loi vitamin no s dn n nhng ri lon v hot ng sinh l bnh thng ca c th. Vitamin c tng hp ch yu thc vt v vi sinh vt. ngi v ng vt cng c th tng hp c mt s Vitamin nhng rt t nn khng tho mn nhu cu ca c th m phi tip nhn thm ngoi vo bng con ng thc n. C nhiu loi Vitamin khc nhau. Tn Vitamin c gi theo nhiu cch nh gi theo ch ci, gi theo danh php ho hc, gi theo chc nng. V d Vitamin B1 cn c tn ha hc l Thiamin, ng thi theo chc nng ca n cn c tn antinevrit. C nhiu kiu phn loi Vitamin, nhng kiu phn loi c s dng ph bin nht l da vo kh nng ho tan