17

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 .

23

24

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.

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

92

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 ca Vitamin vo cc dung mi. Ngi ta chia Vitamin ra 2 nhm: Vitamin tan trong nc v Vitamin tan trong m. Vitamin tan trong nc ch yu tham gia vo cc qu trnh lin quan ti s gii phng nng lng nh qu trnh oxi ho kh, qu trnh phn gii cc hp cht hu c... Vitamin tan trong m tham gia vo cc phn ng to nn cc cht c chc nng cu trc cc m, cc c quan.

5.1. Vitamin tan trong nc5.1.1. Vitamin B1 (Thiamin) Vitamin B1 l loi Vitamin rt ph bin trong thin nhin, c bit trong nm men, cm go, mm la m ... Trong cm go c hm lng Vitamin B1cao nht. Vitamin B1 c tch ra dng tinh th vo nm 1912 v xc nh c cu trc ho hc ca n.

93

NH2 N H3C CH2 N CH3 CH2 - CH2OH S

N

Vitamin B1 bn trong mi trng acid, cn trong mi trng kim n rt d b phn hu khi un nng. Trong c th B1 c th tn ti trng thi t do hay dng Thiamin pyrophosphate. Thiamin pyrophosphate l dng B1 lin kt vi H3PO4 v c vai tr quan trng trong qu trnh trao i cht ca c th. Thiamin pyrophosphate l coenzyme xc tc cho qu trnh phn gii cc ceto acid nh pyruvic acid, oxaloacetic acid.... V vy khi thiu Vitamin B1 s chuyn ho cc ceto acid b ngng tr lm cho c th tch lu mt lng ln cc ceto acid lm ri lon trao i cht v gy nn cc trng thi bnh l nguy him. Vitamin B1 ho tan tt trong mi trng nc v chu nhit kh nn khng b phn hu khi nu nng. B1 c tng hp ch yu thc vt v mt s vi sinh vt. Ngi v ng vt khng tng hp c B1 m phi nhn t ngun thc n. Ngun cha nhiu Vitamin B1 l cm go, ng, la m, gan, thn, tim, no, nht l nm men. Khi thiu B1 c th pht sinh bnh beri-beri, cn gi l bnh t ph, do qu trnh trao i cht b ri lon. Nhu cu Vitamin B1 ph thuc vo iu kin ngh nghip, vo trng thi sinh l ca c th, vo la tui. Nhu cu hng ngy ca ngi ln l 1-3mg, ca tr em 0,5-2mg. 5.1.2. Vitamin B2 (Riboflavin) Vitamin B2 l dn xut ca vng Isoalloxazin, thuc nhm flavin. Trong c th B2 lin kt vi H3PO4 to nn coenzyme FMN v FAD l nhng coenzyme ca h enzyme dehydrogenase hiu kh. trng thi kh Vitamin B2 bn vi nhit v acid. Vitamin B2 c nhiu trong nm men, u, tht, sa, gan, trng. Khi thiu Vitamin B2 s tng hp cc enzyme oxi ho kh b ngng tr lm nh hng n qu trnh oxi ho kh to nng lng cho c th. ng thi khi thiu Vitamin B2 vic sn sinh ra cc t bo ca biu b rut cng

94 b nh hng gy nn s chy mu rut hay ri lon hot ng ca d dy, rut. Vitamin B2 cn gip c th khng khun tt hn. Nhu cu Vitamin B2 hng ngy ca mt ngi khong 2-3mg. CH2 - (CHOH)3-CH2OH

H3C H3C

N

N

O

N O Riboflavin (Vitamin B2)

NH

5.1.3. Vitamin PP (Nicotinic acid, nicotinamid) Vitamin PP l nicotinic acid v amid ca n l nicotinamid. O COOH N N Nicotinic acid Nicotinamid C NH2

Vitamin PP l thnh phn ca coenzyme NAD, NADP c trong cc enzyme thuc nhm dehydrogenase k kh. Vitamin PP gip c th chng li bnh pellagra (bnh da sn si). Khi mc bnh pellagra s dn n sng mng nhy d dy, rut, sau sng ngoi da. Vitamin PP dng nicotinic acid bn vi nhit, acid v c kim nn kh b phn hu, cn dng nicotinamid li km bn vi acid v kim.

95 Vitamin PP khng b bin i khi nu nng nn thc n gi c hm lng PP qua x l. Vitamin PP c nhiu trong gan, tht nc, tim, c bit l nm men. Nu c th thiu Vitamin PP s nh hng n cc qu trnh oxi ho kh. Vitamin PP c tc dng ngn nga bnh ngoi da, sng mng nhy rut, d dy. Hng ngy nhu cu ca mt ngi khong 15-25mg Vitamin PP. 5.1.4. Vitamin B6 (Pyridoxin) Vitamin B6 tn ti trong c th 3 dng khc nhau: Piridoxol, Pyridoxal, Pyridoxamine. Ba dng ny c th chuyn ho ln nhauB

CH2OH HO H3C CH2OH

N Pyridoxol

Vitamin B6 l thnh phn coenzyme ca nhiu enzyme xc tc cho qu trnh chuyn ho amino acid, l thnh phn cu to ca phosphorylase... Vitamin B6 c nhiu trong nm men, trng, gan, ht ng cc, rau qu ... Nu thiu Vitamin B6 s dn n cc bnh ngoi da, bnh thn kinh nh au u, bnh rng tc, rng lng ... Hng ngy mi ngi ln cn 1,5-2,8 mg, vi tr em cn 0,5-2mg Vitamin B6. 5.1.5. Vitamin C (Ascorbic acid) Vitamin C l ascorbic acid. Trong c th Vitamin C tn ti 2 dng: dng kh l ascobic acid v dng oxy ho l dehydro ascobic.

96 CH2OH CHOH O O O O CH2OH CHOH O O

OH

OH

Ascorbic acid

Dehydro ascorbic acid

Vitamin C tham gia nhiu qu trnh sinh l quan trng trong c th: - Qu trnh hydroxyl ho do hydroxylase xc tc. - Duy tr cn bng gia cc dng ion Fe+2/Fe+3, Cu+1/Cu+2. - Vn chuyn H2 trong chui h hp ph. - Lm tng tnh khng ca c th i vi nhng iu kin khng thun li ca mi trng, cc c t ca bnh nhim trng, lm gim cc triu chng bnh l do tc dng ca phng x. Ngoi ra Vitamin C cn tham gia vo nhiu qu trnh khc c vai tr quan trng trong c th. Vitamin C c nhiu trong cc loi rau qu ti, nht l trong cc loi qu c mi nh cam, chanh, bi... Nhu cu hng ngy cn 7080mg/ngi. Nu thiu Vitamin C s dn n bnh hoi huyt, gim sc khng ca c th, b bnh chy mu rng, li hay ni quan (bnh scorbutus). 5.1.6. Vitamin B12 (Cyanocobalamin) Vitamin B12 c cu to phc tp, trong thnh phn c cha nhm CN, CO, amin. Thnh phn chnh ca Vitamin B12 l nhm porphyrin. Vitamin B12 gip cho vic to huyt cu t v hng cu. B12 tham gia cc qu trnh tng hp nucleotide nh xc tc cc phn ng metyl ho cc base Nit. Thiu B12 s gy bnh thiu mu c tnh. Ngoi cc loi Vitamin trn, trong nhm Vitamin tan trong nc cn mt s Vitamin khc nh Vitamin B5, Vitamin Bc, Vitamin H...B B

97

5.2. Vitamin tan trong cht bo5.2.1. Vitamin A (retinol) Vitamin A c 2 dng quan trng l A1 v A2. Vitamin A c hnh thnh t .caroten l tin Vitamin A. T .caroten to thnh 2 phn t Vitamin A.CH3 CH3 CH3 CH3

CH2OH

CH3

Vitamin A1

Vitamin A c nhiu trong du c, lng trng. Trong thc vt c nhiu tin Vitamin A (.caroten) nht l trong c c rt, qu c chua, qu gc,... qu u . Vitamin A c vai tr quan trng trong c ch tip nhn nh sng ca mt, tham gia vo qu trnh trao i protein, lipid, saccharide. Thiu Vitamin A s b bnh qung g, kh mt, chm ln, st cn, gim kh nng khng ca c th i vi cc bnh nhim trng. Nhu cu Vitamin A hng ngy i vi ngi ln 1-2mg, tr em di 1 tui 0,5-1mg. 5.2.2. Vitamin D Trong c th tn ti nhiu loi Vitamin D, trong quan trng nht l dng D2 v D3. Cc Vitamin D l dn xut ca cc sterol. Trong c th Vitamin D c to ra t tin Vitamin D c sn di da nh nh sng mt tri c tia t ngoi. Thiu hoc tha Vitamin D u nh hng n nng photpho v canxi trong mu. Thiu Vitamin D tr em d b bnh ci xng, ngi ln b bnh long xng. Vitamin D c nhiu trong du c, m b, lng trng. Tin Vitamin D c sn trong m ng vt. Hng ngy mi ngi cn khong 10-20mg, tr em di 30 thng cn nhiu hn: 20-40mg.

98 5.2.3. Vitamin E (Tocopherol) Vitamin E c nhiu dng khc nhau. l cc dng , , , ... tocopherol. Cc dng khc nhau ny c phn bit bi s lng v v tr ca cc nhm metyl gn vo vng thm ca phn t. Trong cc loi Vitamin E, dng -tocopherol c hot tnh cao nht:CH3 O H3C HO CH3 CH3 CH3 CH3 CH3

(CH2)3 - CH - (CH2)3 - CH - (CH2)3- CH - CH3

- Tocopherol

Vitamin E c nhiu cc loi rau xanh, nht l x lch, ht ng cc, du thc vt, gan b, lng trng, mm ht ho tho ... Vitamin E c tc dng nh cht chng oxi ho nn c tc dng bo v cc cht d b oxi ho trong t bo. Vitamin E cn c vai tr quan trng trong sinh sn. Nhu cu Vitamin E hng ngy khong 20mg cho mt ngi ln. 5.2.4. Vitamin K C nhiu loi Vitamin K, vi cng thc tng qut l O CH3 R O Vitamin K cn cho qu trnh sinh tng hp cc yu t lm ng mu (prothrombin) cho nn Vitamin K l Vitamin chng chy mu, thiu Vitamin K tc ng mu gim, mu kh ng.

99 Vitamin K c nhiu trong c linh lng, bp ci, rau m, c chua, u, ng cc, lng trng, tht b ... Thng ngi kho mnh, vi khun ng rut c kh nng cung cp Vitamin K cho nhu cu ca c th, ch cn b sung thm khong 0,2-0,3mg/ngy/ngi. 5.2.5. Vitamin F Vitamin F l cc acid bo khng no nh linoleic acid, linolenic acid, arachidonic acid ... Vitamin F c tc dng nui da, tiu m. Thiu Vitamin F ng vt chm ln, vim da, rng lng, hoi t ui. Vitamin F c nhiu trong cc loi du thc vt. 5.2.6. Vitamin Q (Ubiquinon) Vitamin Q ln u tin c tch ra t m ng vt vo nm 1955. Cu trc v chc nng ca Vitamin Q gn tng t nh Vitamin K v F. Vitamin Q tham gia vo cc qu trnh oxi ho-kh ca c th vi chc nng thnh vin ca chui vn chuyn in t ca ty th. Vitamin Q c trong nhiu i tng nh vi sinh vt, thc vt, ng vt .... 5.2.7. Vitamin P (Rutin) Vitamin P l nhm Vitamin c cu trc t flavon. Hin nay ngi ta pht hin khong 150 loi cht flavonoid khc nhau c tc dng nh Vitamin P, trong c 10 cht c nghin cu k. Thiu Vitamin P xy ra hin tng tng tnh thm ca mao qun, chy mu bt thng, mi mt, suy nhc c th. Vitamin P c tc dng lm gim tnh thm ca thnh mao qun. Vitamin P cn c th tham gia vo qu trnh oxi ho kh ca c th nh chc nng ca Vitamin C. Nhu cu Vitamin P khong bng 50% nhu cu Vitamin C.

100

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. Phm Th Trn Chu, Trn Th ng. 2000. Ha sinh hc. Nxb Gio dc, H Ni. 3. Nguyn B Lc. 1997. Ha sinh. Nxb Gio dc, H Ni

Ti liu dch1. Musil J.G., Kurz .K., Novakava .O. 1982 Sinh ha hc hin i theo s . Nxb Y hc, H Ni.

Ti liu ting Anh1. Farkas G. 1984. Nvnyi anyagcserelettan. Akadmiai Kiad Budapest. 2. Lehninger A. L., 2004. Principle of Biochemistry, 4th Edition. W.H Freeman.

101

Chng 6

EnzymeEnzyme l protein c kh nng xc tc c hiu cho cc phn ng ha hc. Chng thc y mt phn ng xy ra m khng c mt trong sn phm cui cng. Enzyme c trong nhiu i tng sinh hc nh thc vt, ng vt v mi trng nui cy vi sinh vt.Hin nay ngi ta thu c nhiu loi ch phm enzyme khc nhau v s dng rng ri trong nhiu lnh vc nh y hc , nng nghip, cng nghip

6.1. Bn cht ha hc ca enzymeNgoi tr mt nhm nh RNA c tnh xc tc, tt c enzyme u l protein. Tnh cht xc tc ph thuc vo cu to ca protein. Nu mt enzyme b bin tnh hay phn tch thnh nhng tiu n v th hot tnh xc tc thng b mt i, tng t khi bn thn protein enzyme b phn ct thnh nhng amino acid. V vy cu trc bc 1, 2, 3, 4 ca protein enzyme l cn thit cho hot tnh xc tc ca chng. Enzyme, cng nh nhng protein khc, c trng lng phn t khong 12.000 n hn 1000.000.Mt s enzyme cu to gm ton nhng phn t L amino acid lin kt vi nhau to thnh, gi l enzyme mt thnh phn. a s enzyme l nhng protein phc tp gi l enzyme hai thnh phn. Phn khng phi protein gi l nhm ngoi hay coenzyme. Mt coenzyme khi kt hp vi cc apoenzyme khc nhau (phn protein) th xc tc cho qu trnh chuyn ha cc cht khc nhau nhng chng ging nhau v kiu phn ng. Mt s enzyme cn ion kim loi cho hot ng nh: Cu2+ Cytochrome oxidase 2+ 3+ Cytochrome oxidase, catalase, peroxidase Fe hoc Fe + K Pyruvate kinase 2+ Mg Hexokinase, glucose 6-phosphatase, pyruvate kinase Mn2+ Arginase, ribonucleotide reductase Mo Dinitrogenase Ni2+ Urease Se Glutathione peroxidase 2+ Zn Carbonic anhydrase , alcohol dehydrogenase, cc carboxypeptidase A v B

102 Mt s coenzyme v chc nng vn chuyn nhm tng ng ca chng nh sau: Biocytin Coenzyme A 5- Deoxyadenosylcobalamin (coenzyme B12) Flavin adenine dinucleotide Lipoate Nicotinamide adenine dinucleotide Pyridoxal phosphate Tetrahydrofolate Thiamine pyrophosphate CO2 Nhm Acyl Nguyn t H v nhm alkyl in t in t v nhm acyl Ion Hydride (:H-) Nhm Amino Nhm 1 Carbon Aldehyde

6.2. C ch tc dngNhng quan im hin nay nhm gii thch c ch tc dng ca enzyme u cho rng khi enzyme (E) tong tc vi c cht (S) s lm gim nng lng hot ha cc phn ng ha sinh. Mun lm gim nng lng hot ha cc phn ng enzyme cn tri qua nhiu giai on trung gian v to thnh phc cht nht nh gia E v S. Khi kt hp vi phn t enzyme, do kt qu ca s cc ha, s chuyn dch ca cc electron v s bin dng ca cc mi lin kt tham gia trc tip vo phn ng s lm thay i ng nng v th nng nn phn t c cht tr nn hot ng v d dng tham gia phn ng. Vic to thnh phc hp E-S giai on u xy ra rt nhanh v rt khng bn. Do sau mt thi gian di mi c chng minh bng thc nghim. Bng chng r rng nht v s tn ti ca phc hp E-S l thnh cng ca hai nh ha sinh Nht Bn K. Iaglu v T. Ozava l tch c phc E-S trong phn ng kh amin bng cch oxy ha (loi tr nhm amine) mt amino acid dy D do oxydase xc tc. Nhn chung ta c th hnh dung c ch tc dng ca enzyme ln c cht to sn phm bng phng trnh tng qut nh sau: E+S ES P+E Giai on 1: E kt hp vi S to thnh E-S. Giai on ny xy ra rt nhanh, nh cc lin kt khng bn nh lin kt hydro, tng tc tnh

103 din, tng tc Van der Waals Mi loi lin kt i hi nhng iu kin khc nhau v chu nh hng khc nhau khi c nc. Giai on 2: Sau khi to phc, c cht c nhng bin i nht nh v mt in t, cu hnh lm c cht tr nn hot ng hn, phn ng c d dng to thnh sn phm P. Trong nhiu phn ng do enzyme xc tc c 2 hay nhiu lai c cht, v d hexokinase xc tc phn ng: ATP + glucose hexokinase ADP + glucose 6 phosphate C ch enzyme xc tc cho phn ng 2 c cht c th nh sau: a/ C ch to phc 3 thnh phn S2

b/ C ch khng to phc 3 thnh phn

y l trng hp c cht th 2(S2) ch kt hp vo enzyme ( trng thi E) sau khi P1 c to thnh.

6.3. Trung tm hot ng (TTH) ca enzymeT kt qu nghin cu v bn cht ho hc, v cu trc trung tm hot ng , c ch tc ng, v trung tm hot ng chng ta c th c mt s nhn xt chung v trung tm hot ng nh sau: - L b phn dng lin kt vi c cht. - Ch chim t l rt b so vi th tch ton b ca enzyme. - Gm cc nhm chc ca amino acid ngoi ra c th c c cc ion kim loi v cc nhm chc ca cc coenzyme.

104

i vi E mt thnh phn: TTH ch gm nhng nhm chc ca cc amino acid nh nhm hydroxy ca serin, carboxy ca glutamic, vng imidazol Cc nhm chc ca cc amino acid c th xa nhau trong chui polypeptide nhng nh cu trc khng gian nn n gn nhau v mt khng gian. i vi E hai thnh phn: TTH cng nh trn, cc nhm chc ca cc amino acid tham gia to thnh TTH lin kt vi nhau bng cc lin kt hydro. Ngoi ra trong TTH ca loi ny cn c s tham gia ca coenzyme v c th c ion kim loi. Theo Fisher TTH c cu trc c nh, khi kt hp vi c cht to phc E-S ta c th hnh dung ging nh cha kha v kha. Ngy nay ngi ta chng minh c rng: TTH ca enzyme ch c cu to hon chnh khi c s tng tc vi c cht (thuyt tip xc cm ng ca Koshland).

6.4. Tnh c hiu ca enzymeNgi ta chia tnh c hiu ra lm 3 kiu: + c hiu phn ng + c hiu c cht + c hiu khng gian a/ c hiu phn ng: l biu hin ca mt enzyme ch thng xuyn xc tc cho mt kiu phn ng nht nh, v d vn chuyn hydro t cht cho (ru bc nht hay ru bc hai) n cht nhn (NAD+ hay NADP+) hay chuyn nhm amin t mt amino acid n mt ceto acid. Cc phn ng loi th nht do dehydrogenase xc tc, cn phn ng loi th hai do aminotransferase xc tc.

105 b/ c hiu c cht: Tu mc ngi ta chia thnh: c hiu tng i v c hiu tuyt i + c hiu tuyt i: Enzyme ch tc dng ln mt c cht nht nh, mt v d c tnh cht kinh in v chuyn ho tuyt i l urease, enzyme ch phn gii ure: Hng trm th nghim trn cc dn xut ca ure u cho thy chng khng b phn gii di tc ng ca urease. Thc ra ngi ta pht hin kh nng phn gii c cht hydroxyure nhng vi tc b hn khong 120 ln. + c hiu nhm tuyt i: Cc enzyme ny ch tc dng ln nhng cht c cng mt kiu cu trc phn t, mt lin kt v c nhng yu cu xc nh i vi nhm nguyn t i vi nhm nguyn t gn lin kt chu tc dng. v d : maltase ch phn gii lin kt glucosidic c to thnh t glucoside ca glucose vi -OH ca monose khc. + c hiu nhm tng i: Cc enzyme khng c nhng yu cu i vi nhm chc gn lin kt chu tc dng. v d lipase thu phn lipid. c/ c hiu khng gian: Cc enzyme ch xc tc cho mt dng ng phn no nh dng L hay dng D, dng cis hay trans m thi.

6.5. Cc yu t nh hng n tc ca phn ng enzyme6.5.1. nh hng ca nng enzyme Trong iu kin d tha c cht, ngha l [S] >>>[E] th tc phn ng ph thuc vo [S], v= K[E] c dng y = ax. Nh ngi ta o [E] bng cch o vn tc phn ng do enzyme xc tc. C nhiu trng hp trong mi trng c cha cht km hm hay hot ho th vn tc phn ng do enzyme xc tc khng ph thuc tuyn tnh vi [E] . v

[E]Hnh 6.1: S ph thuc ca vn tc phn ng vo [E]

6.5.2 nh hng ca nng c cht [S] Ta kho st trng hp n gin nht : ch mt c cht.

106

E v S

(1) Gi v1 l vn tc ca phn ng to thnh phc cht ES. Gi v-1 l vn tc ca phn ng phn ly phc cht ES to thnh Gi v2 l vn tc ca phn ng to thnh E v P (sn phm). v1 = k1[E][S] v-1 = k-1[ES] v2 = k2[ES] Khi h thng t trng thi cn bng ta c: k-1[ES]+k2[ES] = k1[E][S] (k-1+k2)[ES] = k+1[E][S] (2) Gi E0 l nng ban u: [E0]=[E]+[ES]=>[E]=[E0]-[ES] (3) Thay tr s [E] t (3) vo (2) ta c: (k-1+k2)[ES] = k1([E0]-[ES]) [S] k1 [E0] [S] [ES] = -------------k-1+ k2+k1[S] Nu t Km= k-1+k2/ k1 (Km: gi l hng s Michaelis Menten). Ta c : [ES] = [E0][S]/ Km+[S] Mt khc vn tc phn ng to thnh sn phm P l: V = k2[ES] Thay [ES] bng gi tr trn ta thu c: k2[E0] [S] v = ----------------- (4) Km + [S]

107 Qua y ta thy nng enzyme cng cao th vn tc phn ng enzyme cng ln. Vn tc t cc i khi ton b enzyme lin kt vi c cht, ngha l: Vmax= k2[E0] Thay vo phng trnh (4) ta c: [S] v = Vmax ---------(5) Km+ [S] Phng trnh (5) gi l phng trnh Michaelis Menten. Km gi l hng s Michaelis Menten c trng cho mi enzyme Km c trng cho i lc ca enzyme vi c cht, Km c tr s cng nh th i lc ca enzyme vi c cht cng ln, ngha l vn tc ca phn ng do enzyme xc tc cng ln.

[S]Hnh 6.2. Bin thin vn tc phn ng theo nng c cht.

Khi tng [S] th v phn ng tng, tng [S] n mt gi tr no th v t n gi tr vmax v s khng tng na nu ta vn tip tc tng [S]. Khi Km=[S] th v =1/2 Vmax Nm 1934. Lineweaver v Burk, trn c s ca phng trnh (5) nghch o bin thnh dng ng thng y=ax+b, n c ngha ln i vi vic nghin cu km hm enzyme.

108

1/v

1/Vmax -1/Km 1/[S]

Hnh 6.3: S ph thuc ca tc phn ng vo nng c cht theo Lineweaver-Burk

6.5.3. nh hng ca cht km hm (inhibitor) L cht c tc dng lm gim hot hay lm enzyme khng cn kh nng xc tc bin c cht thnh sn phm. Km hm enzyme c th thc hin bng nhiu cch khc nhau (thun nghch hay khng thun nghch). Thun nghch c: Cch 1: Km hm cnh tranh (competitive inhibition) Trong trng hp km hm cnh tranh l c cht v cht km hm u tc dung ln trung tm hot ng ca enzyme, Cht km hm chon ch ca c cht enzyme.

Hnh 6.4. Kiu km hm cnh tranh

Khi c cht d tha, nng cht km hm thp th c th loi b tc dng ca cht km hm, cn nng c cht thp v nng cht km hm cao th li c tc dng km hm hon ton.

1/v= (Km/Vmax) 1/S +1/Vmax

= 1+[I]/KI

109 1/v

[I]

1/Vmax

Khng c cht km hm

1/[S]Hnh 6. 5. S ph thuc ca tc phn ng vo nng c cht theo Lineweaver-Burk khi c km hm cnh tranh

Ngi ta thy km hm nh vy phn ln xy ra gia cht km hm v c cht c s tng ng v mt ho hc. v d: malic acid c cu trc gn ging vi succinic acid nn km hm cnh tranh enzyme succinatedehydrogenase, l enzyme xc tc cho s bin i succinic acid thnh acid fumaric acid. Trng hp c bit ca km hm cnh tranh l km hm bng sn phm. Trng hp ny xy ra khi mt sn phm phn ng tc dng tr li enzyme v chon v tr hot ng phn t enzyme. ng thng c cht km hm th c xin ln hn v ct trc tung mt im l 1/Vmax Cch 2: Km hm phi cnh tranh (uncompetitive inhibition) c trng ca kiu km hm ny l cht km hm ch lin kt vi phc hp ES, m khng lin kt vi enzyme t do.

110

Hnh 6.6. Kiu km hm phi cnh tranh

1/v=(Km/Vmax)1/[S] + /Vmax1/v [I]

-1/Km

khng c cht km hm

1/[S]Hnh 6.7. S ph thuc ca tc phn ng vo nng c cht theo Lineweaver-Burk khi c km hm phi cnh tranh

111

Cch 3: Km hm hn tp( mixed inhibition )

Hnh 6.8. Kiu km hm hn tp

Trong , cht km hm khng nhng lin kt vi enzmye t do m cn lin kt vi c phc hp ES to thnh phc hp EIS khng to c sn phm P. Tng t nh trn ta c phng trnh :

1/v= (Km/Vmax)1/[S] +/vmax1/v [I]

1/Vmax

khng c cht km hm

1/[S]Hnh 6.9. S ph thuc ca tc phn ng vo nng c cht theo Lineweaver-Burk khi c km hm hn tp

112 Cc gi tr , c nh ngha nh trn. Trng hp = gi l km hm khng cnh tranh (noncompetitive inhibition). Mt trng hp km hm cn gp na l km hm enzyme bng nng cao ca c cht gi l km hm c cht nh km hm urease khi nng ure cao, ngoi ra cn c cc enzyme khc nh lactatdehydrogenase, carboxypeptidase, lipase, pyrophotphatase, photphofructokinase (i vi ATP). Nguyn nhn ca nhng hin tng ny cn cha c bit r. c th l: + Tn ti nhiu trung tm lin kt vi c cht bng cc i lc khc nhau. Khi nng c cht thp th enzyme c th ch lin kt vi mt phn t c cht, cn khi nng c cht cao n lin kt vi nhiu c cht dn n hnh thnh phc hp ES khng hot ng. + C cht cng c th c lin kt nh nhng v tr c bit ca enzyme. l mt nhm enzyme quan trng (enzyme d lp th) bn cnh trung tm xc tc cn c trung tm iu chnh. + C cht c th lin kt vi mt cht hot ho v bng cch ny n tch khi E. + C cht c th chon ch (ngn cn) mt cofactor ( ng yu t ) hay mt coenzyme. + C cht c th nh hng n ion lc ca mi trng v qua lm mt i tnh chuyn ho ca enzyme. 6.5.4. nh hng ca cht hot ha (activator) L cht lm tng kh nng xc tc nhm chuyn ha c cht thnh sn phm. Thng thng l nhng cation kim loi hay nhng hp cht hu c nh cc vitamin tan trong nc. V d: Mg++ hot ha cc enzyme m c cht c phosphoryl ha nh pyrophosphatase (c cht l pyrophosphate), adenosinetriphosphatase (c cht l ATP). Cc cation kim loi c th c tnh c hiu, tnh i khng v tc dng cn tu thuc vo nng . 6.5.5. nh hng cu nhit Ta c th tng vn tc ca mt phn ng ha hc bng cch tng nhit mi trng, hin tng ny tun theo quy lut Vant-Hoff. iu ny c ngha khi tng nhit ln 100C th tc phn ng tng ln khang 2 ln. i vi phn ng do enzyme xc tc cng c th p dng c quy lut ny nhng ch trong mt phm vi nht nh,v bn cht enzyme l protein.Khi ta tng nhit ln trn 40-500C xy ra qu trnh ph hu cht

113 xc tc. Sau nhit ti u tc phn ng do enzyme xc tc s gim. Nh tn ti nhit ti u ngi ta phn bit phn ng ho sinh vi cc phn ng v c thng thng. Mi enzyme c mt nhit ti u khc nhau, phn ln ph thuc ngun cung cp enzyme, thng thng trong khong t 40-600C , cng c enzyme c nhit ti u rt cao nh cc enzyme ca nhng chng a nhit. Cc chng vi sinh vt a nhit, c bit cc vi khun chu nhit c cha enzyme chu nhit cao. Hat

nhit Hnh 6.10. nh hng ca nhit ln hat enzyme

6.5.6. nh hng ca pH S phn li khc nhau ca mt phn t protein cc gi tr pH khc nhau lm thay i tnh cht ca trung tm lin kt vi c cht v tnh cht hot ng ca phn t enzyme.iu ny dn n gi tr xc tc khc nhau ph thuc vo gi tr pH. Nh bit mi enzyme c mt pH ti u,mi enzyme c ng biu din nh hng pH ln vn tc phn ng do chng xc tc. ng biu din c dng nh hnh sau: Hat

Hnh 6.10. nh hng ca pH ln hat enzyme

114 nh hng ca gi tr pH n tc dng enzyme c th do cc c s sau: a/ Enzyme c s thay i khng thun nghch phm vi pH cc hp. b/ hai sn ca pH ti u c th xy ra s phn ly nhm prosthetic hay coenzyme. c/ Lm thay i mc ion ho hay phn ly c cht. d/ Lm thay i mc ion ho nhm chc nht nh trn phn t enzyme dn n lm thay i i lc lin kt ca enzyme vi c cht v thay i hot tnh cc i. Nh xc nh Vmax v Km ph thuc gi tr pH cho php nhn nh li bn cht ca cc nhm tham gia vo lin kt c cht v qu trnh t xc tc. 6.5.7. Cc yu t khc + nh sng: C nh hng khc nhau n tng loi enzyme, cc bc sng khc nhau c nh hng khc nhau, thng nh sng trng c tc ng mnh nht, nh sng c tc ng yu nht. nh sng vng t ngoi cng c th gy nn nhng bt li, enzyme trng thi dung dch bn hn khi c kt tinh dng tinh th, nng enzyme trong dung dch cng thp th cng km bn, tc ng ca tia t ngoi s tng ln khi nhit cao. V d di tc ng ca tia t ngoi nhit cao enzyme amylase nhanh chng mt hot tnh. + S chiu in: in chiu vi cng cng cao th tc ng ph hu cng mnh. Tc ng s mnh hn i vi dch enzyme c nng thp. C th do to thnh nhng gc t do, t tn cng vo phn ng enzyme. + Sng siu m: Tc ng rt khc nhau i vi tng loai enzyme, c enzyme b mt hot tnh, c enzyme li khng chu nh hng. Nhn xt chung: bn ph thuc vo trang thi tn ti ca enzyme, cng tinh khit th enzyme cng km bn, dch cng long th bn cng km, tc ng ca mt s ion kim loi trong dch vi nng khong 10-3M nh Ca++ lm tng tnh bn. Enzyme allosteric ( Enzyme d lp th, d khng gian) Cho n nay, ngi ta m t enzyme m hat tnh enzyme ph thuc nng c cht khng c dng hyperbol m c dng sigmoid l enzyme allosteric (Hnh 6.11 ):

115

Hnh 6.11. Bin thin vn tc phn ng theo nng c cht

i vi enzyme ny, khi nng c cht thp th tc phn ng tng chm, sau tip tc tng nng th tc nhanh chng t gi tr cc i. Nh ta bit, enzyme tun theo ng hc Michaelis-Menten th 1 hay nhiu c cht cng ch lin kt vo 1 v tr trn phn t enzyme, iu ny s dn n enzyme bo ha c cht. Cn enzyme c ng cong tc sigmoid ch xut hin khi enzyme l mt oligomer, nn c th lin kt vi nhiu phn t c cht. iu ny c ngha trn enzyme allosteric c nhiu trung tm lin kt, mi monomer c 1 trung tm lin kt. Ngi ta cho rng, trong trng hp ny c tnh hp tc gia cc v tr lin kt c cht trong phn t enzyme oligomer. Cc enzyme oligomer ny c Monod gi l allosteric enzyme d lp th (allosteric enzyme). ng cong tc sigmoid c th b cht iu ha (modulator) y v pha tri hay phi. Cht iu ha dng tc lm tng i lc ca enzyme allosteric vi c cht, ngc li l cht iu ha m. Cc cht iu ha c th lm nh hng khc nhau n cc thng s ng hc, lm thay i gi tr ring l mt trong hai gi tr Km hay Vmax.

Hnh 6.12 Minh ha khi c modulator

116

6.6. Cch gi tn v phn loi enzymeNh ta bit mi enzyme xc tc cho mi kiu phn ng ho hc duy nht (nh oxy ho mt kiu c cht nht nh, thu phn mt kiu lin kt nht nh,vn chuyn mt nhm cht nht nh t mt cht cho n mt cht nhn c a ch, trong c c vic bin i ch mt c cht duy nht), mt khc cn c mt kiu phn ng ho sinh nht nh c th c xc tc bng cc enzyme khc nhau. Da vo tnh c hiu phn ng ca enzyme, nm 1961 tiu ban enzyme hc quc t trnh by mt bo co, trong c ngh nhng nguyn tc nh tn v phn loi enzyme. Ngi ta chia enzyme ra lm 6 lp: 1. Oxydoreductase: cc enzyme xc tc cho cc phn ng oxi ho-kh. 2. Transferase: cc enzyme xc tc cho cc phn ng chuyn v. 3. Hydrolase: cc enzyme xc tc cho cc phn ng thy phn. 4. Lyase: cc enzyme xc tc cho cc phn ng phn ct khng cn nc. 5. Isomerase: cc enzyme xc tc cho cc phn ng ng phn ho. 6. Ligase (synthetase): cc enzyme xc tc cho cc phn ng tng hp c s dng lin kt giu nng lng ca ATP .v.v. Mi lp chia thnh nhiu t (di lp), mi t chia thnh nhiu nhm (siu lp). Tn enzyme thng c gi: Tn c cht c hiu - loi phn ng xc tc cng thm tip v ng ase. ng trc tn enzyme thng c 4 con s: s th nht ch lp, s th hai ch t, s th ba ch nhm, s th t ch s hng enzyme trong nhm. V d: (2.6.1.1) L.aspartate: -cetoglutarate aminotransferase. Enzyme ny xc tc cho phn ng chuyn nhm amine t L.aspartate n -cetoglutarate. L.aspartate +-cetoglutarate oxaloacetate + glutamate

6.7. Cc coenzyme quan trng

Nicotinamide adenine dinucleotide

117

Flavine adenine dinucleotide

Lipoic acid

Coenzyme A

Biotin

118

Thiamin diphosphate

(Nhm - amino protein, Schiff base)

Pyridoxal phosphate

Tetrahydrofolic acid

119

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. Bergmeyer H. U. 1968. Methods of enzymatic analysis, translated from the third German edition, Acanamic, New York. 2. Copeland R. A. 2000. Enzymes, copyright by Wiley-VCH, Inc. 3. Lehninger A. L. 2004. Principles of Biochemistry, 4th Edition. W.H Freeman. 4. Mikkelsen S. R. 2004. Bioanalytical chemistry, copyright by John Wiley & Sons, Inc.

120

Chng 7

Hormone7.1. C ch tc dng ca hormoneHormone l nhng cht hu c c to thnh trong c th c tc dng iu ho cc hot ng sng trong c th. Lng hormone trong c th thng rt thp. Hormone c c thc vt v ng vt. ng vt hormone c sn xut ti cc tuyn ni tit v tc ng n cc m khc ni n c to ra. Hormone t tuyn ni tit c tit trc tip vo mu v c mu vn chuyn n cc m chu tc dng. Hormone c tnh c hiu. Hormone c tc dng iu ho cc qu trnh sinh l, ho sinh trong c th m khng tham gia trc tip vo cc phn ng ca c th. Hormone c tc ng n tc sinh tng hp protein, enzyme, nh hng n tc xc tc ca enzyme; thay i tnh thm ca mng t bo, qua iu ho hot ng sng xy ra trong t bo. Mt s hormone tc ng n c th thng qua cht trung gian AMP vng. AMP vng l cht truyn tin th 2, cn hormone l cht truyn tin th nht. Theo c ch ny tc dng ca hormone ln t bo ch xy ra qua nhiu giai on kh phc tp. - Trong mng nguyn sinh cht ca t bo c cha cht nhn hormone, cht ny s kt hp c hiu vi hormone. - S kt hp kch thch lm tng hot ca adenylatcyclase xc tc cho phn ng chuyn ho ATP thnh AMP vng. - Adenylatcyclase xc tc cho phn ng chuyn ho ATP thnh AMP vng. - AMP vng lm thay i vn tc ca cc qu trnh xy ra trong t bo lin quan n hot ng ca hormone. - Nh vy tc dng ca hormone theo c ch ny phi thng qua AMP vng m khng tc ng trc tip vo t bo. - Qu trnh hot ho adenylatcyclase bi phc hormone-cht nhn c thc hin qua cht trung gian l protein G. Phn t protein ny c kh nng kt hp vi GDP hay GTP. Dng phc protein G-GTP c tc dng hot ho adenylatcyclase, cn protein G-GDP khng c tc dng ny. Nh vy mun chuyn sang dng hot ng phi c s tham gia ca GTP, nu l protein G-GDP cn c s thay th GDP bng GTP nh phc

121 hormone-cht nhn xc tc. Dng thng tin c truyn t cht nhn hormone n protein G ri n adenylatcyclase. - Protein G khng ch c vai tr trung gian mang thng tin t cht nhn hormone n adenylatcyclase m cn c hot tnh ca GTPase, l kh nng thu phn GTP. Nh kh nng nn n xc tc cho qu trnh chuyn phc proteinG-GTP hot ng thnh dng proteinG-GDP khng hot ng do thu phn GTP trong phc proteinGTP thnh GDP to nn phc proteinG-GDP. Bng c ch protein G c vai tr quan trng trong qu trnh hot ho hay phn hot ho adenylatcyclase. Khi lng hormone gim adenylatcyclase tr thnh dng khng hot ng. - Nhiu hormone c c ch tc ng thng qua vai tr trung gian ca AMP vng. Nh vy AMP vng tham gia vo nhiu qu trnh khc nhau trong c ch tc ng ca hormone. l do AMP vng c tc dng hot ho proteinkinase l enzyme xc tc qu trnh photphoryl ho nhiu loi protein khc nhau. Thng cc protein enzyme dng phosphoryl ho l dng c hot tnh sinh hc. - Cc hormone tc dng theo c ch qua AMP vng, tn hiu c khuych i ln nhiu ln, do vy nng cc hormone trong mu rt thp, ch khong 10-10M, nhng ch cn hot ho c mt phn t adenylatcyclase c th to ra c nhiu phn t AMP vng nn nng AMP vng trong t bo ch cao hn nhiu lng hormone trong mu. Tc dng hot ho proteinkinase nh AMP vng li lm cho tn hiu c khuych tn tip tc v nhiu phn t protein c hot ho nh proteinkinase. iu gii thch c ti sao nng hormone trong mu rt thp m tc dng kch thch ca n li rt mnh. - Mt c ch tc ng th hai ca hormone l khng qua AMP vng.Insulin l hormone tc ng n t bo ch khng qua bc trung gian l lm tng lng AMP vng. Insulin lin kt cht ch vi cht nhn c hiu ca n trn mng nguyn sinh cht ca t bo ch. Tng tc gia Insulin v cht nhn bo m cho tc ng ca Insulin c th hin nhanh chng. Insulin cn c tc dng phosphoryl ho protein tham gia vo c ch kch thch qu trnh trao i glycogen. - C ch tc dng ca cc hormone thc vt hon ton khc hormone ng vt. Cc hormone thc vt tc ng ln hot tnh cc enzyme bng cch lin kt vi enzyme to phc hot ng. Khi lin kt vi hormone hot tnh ca enzyme c tng ln. - Hormone thc vt cn lm thay i tnh cht ca mng cellulose, mng nguyn sinh qua tc ng kch thch qu trnh sinh trng ca t bo.

122 - Mt c ch tc ng quan trng na ca hormone thc vt l thay i tnh cht ca nguyn sinh cht ca t bo, t nh hng n cc hot ng sinh l, trao i cht ca t bo

7.2. Cc hormone quan trng7.2.1. Hormone ng vt - Hormone ng vt c nhiu loi vi cu to v chc nng rt khc nhau. Da vo cu to ho hc c th chia hormone ng vt thnh 3 nhm: - Hormone steroid l dn xut ca cholesterol. - Hormone l dn xut ca amino acid. - Hormone l peptide hay protein. 7.2.1.1. Hormone l steroid - y l nhm hormone c s lng ln, c vai tr quan trng v a dng. Ngi ta chia steroid thnh 5 nhm nh vi nhiu loi khc nhau:T T 1 Nhm Progestagen i din Progesterol Ni to thnh -Th vng -V thng thn Vai tr Hormone dng thai gip trng pht trin - Kch thch tng glycogen v tch glycogen gan. - Kch thch phn protein, lipid. - Chng vim, nc mui. hp lu gii tch

Glucocorticoid 2

Cortisol

V thng thn

3 4

Mineral corticoid

Andosterol

V thng thn Tinh hon

- Tng hp th Na+, Cl- Tng tch nc. - Bi tit K+ Pht trin cc c im ca nam gii.

Androgen

Testosterol

5

Estrogen

Estron

- Pht trin cc c im n gii. Bung trng - Pht trin nim mc d con.

123 7.2.1.2. Hormone l dn xut amino acid n nay ngi ta bit mt s hormone l dn xut amino acid nh adrenaline, noradrenaline, thyroxine... - Adrenaline v noradrenaline l cc hormone do tuyn thng thn to ra. Cc hormone ny c tc dng kch thch s phn gii glycogen, lm gim s tng hp glycogen nn lm tng hm lng glucose trong mu. . OH

HO

CHOH - CH2 - NH - CH3 Adrenaline OH CHOH - CH2 - NH2 Noradrenaline

HO

Thiroxine l hormone do tuyn gip sn xut c tc dng tng cng qu trnh trao i cht, gip cho c th pht trin bnh thng. Nu thiu thyroxine gy nn trng thi thiu nng tuyn gip lm cho c th ln, km pht trin, n n. Ngc li nu tha thyroxine cng gy bnh l u nng tuyn gip lm cho ngi cao qu kh, khng cn i. I HO I O I Thyroxine (Tetraiodothyronine) I CH2 - CH NH2 COOH

124 y l nhm hormone c vai tr quan trng trong qu trnh iu ho trao i cht trong c th, c bit l iu ho lng ng trong mu. Mt s hormone l peptide:STT 1 2 3 4 5 6 7 8 9 10 Hormone Tyrocalcitonin Insulin Glucagon Oxytoxin (HGF) Vasopressin (ADH) Melanotropin (MSH) Somatotropin (STH) Corticotropin (ACTH) Thyreotropin (TSH) Kch nang t (FSH) Ni to ra Tuyn ty Tuyn ty Tuyn yn Tuyn yn Tuyn yn Tuyn yn Tuyn yn Tuyn yn Tuyn yn Vai tr Gim lng ng trong mu Tng lng ng trong mu Gy co d con, kch thch Tng p, chng bi tit Kch thch tng sc t da Kch thch tng trng, tng TC Kch thch tuyn trn thn Kch thch tuyn gip Kch thch to estradiol

Tuyn gip Gim hm lng Ca++ trong mu

Sau y s cp n mt s hormone trong nhm ny: - Insulin: Insulin c tit t t bo beta ca o Langhan ca tuyn ty khi lng ng trong mu cao. Insulin kch thch cc qu trnh tng hp, km hm cc qu trnh phn gii glycogen gan, m m. Insulin cn kch thch s phn gii glucose. Nh insulin lm gim lng ng trong mu, do chng li bnh i tho ng. Insulin c khi lng phn t l 5800. Cu to insulin gm 2 chui polypeptide: chui A c 21 amino acid, chui B c 30 amino acid. Hai chui lin kt vi nhau bng 2 lin kt disunfit. Tin cht ca insulin l proinsulin v preproinsulin.T preproinsulin bin i thnh proinsulin, sau insulin c to nn t proinsulin. - Glucagon l hormone peptide, c tc dng ngc vi insulin. Khi lng ng trong mu gim qa mc cho php th tuyn tu sn sinh ra glucagon c tc dng lm tng lng ng trong mu nh km hm qu trnh tng hp glycogen. Glucagon c khi lng phn t 3.500, bao gm 29 gc amino acid to chui polypeptide mch thng.

125 7.2.2. Hormone thc vt Hormone thc vt l cc cht c vai tr quan trng trong qu trnh sinh trng, pht trin ca thc vt. C nhiu loi hormone khc nhau trong c th thc vt. Cc loi hormone ny khc nhau v bn cht ho hc, v vai tr i vi thc vt. C th chia hormone thc vt thnh 5 nhm: - Auxin. - Gibberellin. - Cytokinin. - Absisic acid. - Ethylen. 7.2.2.1. Auxin Auxin l nhm hormone quan trng, ph bin nht thc vt. C nhiu loi auxin khc nhau vi cu trc ho hc khc nhau. Loi auxin quan trng nht l -indol-acetic acid (IAA), ngoi ra mt s auxin khc cng kh ph bin l napthalen-acetic acid (NAA), phenyl-acetic acid (PAA) ...CH2-COOH CH2-COOH

CH2-COOHN H

IAA

NAA

PAA

Auxin c vai tr nhiu mt i vi thc vt: - Kch thch s sinh trng t bo, t kch thch s sinh trng cc c quan v ton c th. - C vai tr quyt nh hin tng u th nh. - C vai tr quyt nh cc c ng sinh trng nh hng sng, hng trng lc. - Kch thch qu trnh ny mm, rt ngn thi k ng ca ht, c. - c ch s rng l, kch thch s to qu.

126 - Kch thch cc hot ng sinh l, cc qu trnh trao i cht v nng lng ca c th. 7.2.2.2. Gibberellin Gibberellin l nhm hormone quan trng th hai thc vt. Gibberellin c cc nh khoa hc Nht pht hin ln u tin loi nm gy bnh la von (Gibberellin fujcoroi). C nhiu loi Gibberellin khc nhau, n nay tm thy hn 70 loi Gibberellin c mt thc vt, vi sinh vt. Ngi ta t tn cc Gibberellin theo th t thi gian pht hin GA1. GA2 .... GAn, trong quan trng nht c th k n l GA3. Cc Gibberellin u l dn xut ca vng gibban.

O

HO

C=O

OH COOH CH2

CH3

Cu to GA3 Gibberellin c vai tr quan trng trong qu trnh sinh trng, pht trin ca thc vt: - Kch thch s sinh trng ca t bo, qua kch thch s sinh trng ca cc c quan v c th. - Kch thch qu trnh ny mm, ph trng thi ng ca ht, c. - Kch thch s ra hoa ca cy ngy di. - Kch thch cc hot ng sinh l, cc qu trnh trao i cht v nng lng ca c th. 7.2.2.3. Cytokinin Cytokinin l cc dn xut ca base Adenine. C nhiu loi cytokinin khc nhau, quan trng nht l kinetin v zeatin.

127

HN - CH2

ON

HN - CH2- CH = CH

CH2OH CH3

N

N

N N H N N N H

N

Kinetin

Zeatin

Xitokinin tham gia v nhiu hot ng sng quan trng ca thc vt: - Kch thch s phn bo qua kch thch s sinh trng ca t bo. - Lm chm qu trnh ho gi ca t bo, m. - Gip cho thc vt chng li cc stress ca mi trng c hiu qu. - L thnh phn cu to ca nucleic acid (trong mt s loi RNA) nn c vai tr trong qu trnh trao i nucleic acid v protein. - Kch thch cc hot ng sinh l, cc qu trnh trao i cht v nng lng ca c th. 7.2.2.4. Absisic acid Acid absisic (ABA) l nhm cht c ch sinh trng c tc dng ngc li 3 nhm cht trn. Absisic acid l dn xut ca triterpen. CH3 CH3OH COOH O

CH3

CH3 ABA

128 Tc dng ch yu ca ABA l c ch qu trnh sinh trng ca t bo, gy hin tng rng l, rng qu. ABA ko di thi gian ng ca ht, c. Do c ch s sinh trng ca thc vt nn ABA phi hp vi nhm cht kch thch sinh trng iu ho qu trnh sinh trng ca thc vt xy ra cn i. 7.2.2.5. Ethylen Ethylen (CH2 = CH2) l nhm hormone thc vt c tc dng gn ging ABA nn thuc nhm cht c ch sinh trng. Etylen thc y qu trnh chn ca qu, qu trnh rng l. Khc vi hormone ng vt, hormone thc vt c tng hp trong cc phn khc nhau ca cy m khng c cc tuyn tit chuyn bit. Cc hormone thc vt c tng hp cc vng khc nhau ca cy. Auxin, gibberellin ch yu c tng hp ti cc phn non ca cy, nht l vng sinh trng nh nh sinh trng, tng tng Sau khi tng hp Auxin, gibberellin c vn chuyn trong cc m dn hay qua h thng t bo sng a n cc vng tc dng. Hormone thc vt cng khng c t bo ch chuyn bit nh ng vt m tc ng ln ton c th. Cytokinetin c tng hp mnh phn r non, cn absisic acid , ethylen l c tng hp nhiu cc phn gi ca cy. Sau khi tng hp cc hormone ny cng c vn chuyn n cc vng khc nhau trong c th thc hin cc chc nng ca chng.

129

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. Phm Th Trn Chu, Trn Th ng. 2000. Ha sinh hc. Nxb Gio dc. H Ni. 3. Nguyn B Lc. 1997. Ha sinh. Nxb Gio dc. H Ni

Ti liu dch1. Musil J.G., Kurz .K., Novakava .O. 1982 2. Sinh ha hc hin i theo s . Nxb Y hc. H Ni.

Ti liu ting nc ngoi1. Farkas G. 1984. Nvnyi anyagcserelettan. Akadmiai Kiad Budapest. 2. Lehninger A. L., 2004. Principle of Biochemistry, 4th Edition. W.H Freeman.

130

Chng 8

Khi nim v s trao i cht v trao i nng lngTrao i cht v trao i nng lng l bn cht ca hot ng sng ca mi c th sinh vt, l biu hin tn ti s sng. S trao i cht ca c th lun gn lin vi s trao i v chuyn ha nng lng. Chnh v vy, trao i cht v trao i nng lng l hai mt ca mt qu trnh lin quan cht ch vi nhau.

8.1. Khi nim chung v s trao i chtC th sng tn ti, pht trin trong mi trng v khng ngng lin h mt thit vi mi trng . N hp th cc cht khc nhau t mi trng ngoi, lm bin i cc cht v mt mt to nn cc yu t cu to ca bn thn c th sng, mt khc li thi vo mi trng ngoi cc sn phm phn gii ca chnh c th cng nh cc sn phm hnh thnh trong qu trnh sng ca c th. Qu trnh thc hin c l do cc bin i ha hc lin tc xy ra trong c th. Ngi ta gi ton b cc bin i ha hc l s trao i cht. S trao i cht bao gm nhiu khu chuyn ha trung gian. Cc qu trnh ny xy ra phc tp trong tng m, tng t bo bao gm 2 qu trnh c bn l ng ha (tng hp) v d ha (phn gii) to nn chu k trao i cht lin tc gia cht nguyn sinh v cht nhn vo. Qu trnh ng ha l s hp th cc cht mi t mi trng bn ngoi, bin i chng thnh sinh cht ca mnh; bin i cc cht n gin thnh cht phc tp hn, s tch ly nng lng cao hn. y l qu trnh bin i cc cht khng c hiu (cc cht hu c ca thc n nh glucid, lipid, protein) t cc ngun khc nhau (thc vt, ng vt, vi sinh vt) thnh cc cht hu c khc (glucid, lipid, protein) c hiu ca c th. c im ca qu trnh ny l thu nng lng. Nng lng cn thit cung cp cho cc phn ng tng hp trn ch yu dng lin kt cao nng ca ATP. Qu trnh d ha l qu trnh ngc li ca qu trnh ng ha, l s bin i cc cht phc tp thnh cc cht n gin v gii phng nng lng cn thit cho hot ng sng. Nh vy y l qu trnh phn gii cc cht d tr, cc cht c trng ca c th thnh cc sn phm phn t nh khng c trng v cui cng thnh nhng cht thi (CO2, H2O,

131

NH3...) thi ra mi trng. Nng lng c tch tr trong ATP v c s dng cho nhiu phn ng thu nng lng khc. Hai qu trnh ng ha v d ha xy ra lin tc lin quan vi nhau v khng tch ri nhau. Qu trnh ng ha l qu trnh i hi nng lng cho nn ng thi phi xy ra qu trnh d ha cung cp nng lng cho qu trnh ng ha. Do s trao i cht v trao i nng lng l hai mt ca mt vn . Ty theo kiu trao i cht, ngi ta chia sinh vt ra thnh hai nhm: nhm sinh vt t dng v nhm sinh vt d dng. Nhm sinh vt t dng bao gm tt c cc sinh vt t tng hp cht dinh dng cn thit cho chng. tn ti v pht trin, nhm ny ch cn H2O, CO2, mui v c v ngun nng lng. C hai hnh thc t dng. l hnh thc t dng quang hp v hnh thc t dng ha hp. Hnh thc u th hin cy xanh v vi khun ta, vi khun lu hunh vn dng quang nng tng hp cht hu c. Hnh thc sau c th hin mt s vi khun nhn nng lng trong qu trnh oxy ha cc cht v c. Nhm sinh vt d dng bao gm cc sinh vt khng c kh nng t tng hp cht dinh dng t cc cht v c m phi sng nh vo cc cht dinh dng ca nhm sinh vt t dng tng hp nn. Nh vy, qu trnh trao i cht ca th gii sinh vt lin quan cht ch vi nhau, to nn chu k trao i cht chung. nh sng Glucid, lipid, protein O2

Sinh vt t dng

Sinh vt d dng

CO2, H2O, mui cha Nitrogen Ngoi cch chia trn, cng theo kiu trao i cht, ngi ta chia sinh vt thnh hai nhm ln: nhm hiu kh (aerob) v nhm k kh (anaerob).

132

Nhm hiu kh l kiu trao i cht m cc qu trnh oxy ha c s tham gia ca oxy kh quyn. Nhm k kh l kiu trao i cht m cc qu trnh oxy ha khng c s tham gia ca oxy kh quyn. a s cc sinh vt thuc nhm hiu kh. Nhm k kh ch l mt phn nh ca nhm sinh vt d dng bc thp. Tuy vy, gia cc c th hiu kh v k kh khng c ranh gii r rng. Sinh vt hiu kh biu hin r rng nht nh ngi chng hn cng c thc hin mt phn cc qu trnh trao i cht theo con ng k kh (v d nh m c) Qu trnh chuyn ha trong c th sng mang tnh thng nht v ring bit. Cc con ng chuyn ha ln trong mi c th ng vt, thc vt n bo, a bo u theo nhng giai on tng t nhau. Tuy vy, nu i su vo tng m, c quan, c th tng loi th li c nhng nt ring bit. Cc phn ng ha hc trong c th xy ra lin tc pH trung tnh, 370C, di tc dng xc tc ca enzyme. ng vt, cc qu trnh chuyn ha c iu khin bi h thng thn kinh

8.2. Khi nim chung v trao i nng lng v nng lng sinh hcTrao i cht lun gn lin vi trao i nng lng. i vi c th ngi, ng vt v phn ln vi sinh vt th ngun nng lng duy nht l nng lng ha hc ca cc cht trong thc n. Trong c th, cc cht dinh dng ch yu v quan trng l glucid, lipid v protein u b oxy ha. Lipid v glucid i vo c th b t chy s sinh ra CO2, H2O v NH3, cht ny tc dng vi CO2 chuyn thnh carbamid (ure). Cc qu trnh oxy ha kh sinh hc thuc cc phn ng d ha c ngha rt quan trng. Chng khng nhng ch l ngun nng lng quan trng dng thc hin cc phn ng tng hp khc nhau m cn l ngun cung cp cc hp cht trung gian dng lm nguyn liu cho cc phn ng tng hp v ng vai tr ht sc quan trng trong vic lin hp cc qu trnh trao i cht. tn ti v pht trin, c th cn phi c cung cp lin tc nng lng. Trong hot ng sng ca mnh, c th bin i nng lng t dng ny sang dng khc v s bin i nng lng trong c th sng cng tun theo cc quy lut vt l nh s bin i nng lng gii v c.

133

So snh v nng lng sinh hc v nng lng k thut ta thy c nhng c im sau: th nht, c th khng s dng nhit nng thnh cng c ch c; th hai, s gii phng nng lng trong c th l dn dn, tng bc; th ba, s gii phng nng lng i km theo s phosphoryl ha ngha l nng lng gii phng c c nh li lin kt este vi phosphoric acid trong phn t ATP vn c gi l lin kt cao nng. T dng nng lng trung gian ny (ATP) m c th d tr v s dng nng lng vo cc hot ng sng; th t, c th khng s dng c nng lng t do ca tt c cc loi phn ng pht nhit m ngun nng lng duy nht c th s dng l ca cc qu trnh oxy ha. 8.2.1. S bin i nng lng t do S thay i v i lng ca nng lng t do l mt ch tiu quan trng nht ca hiu ng nng lng tc l h s ca tc dng hu hiu ca phn ng. C th nh ngha nng lng t do l lng nng lng m mt nhit nht nh no c th bin thnh cng. T bo c th to ra v duy tr c cu trc trt t v phc tp ca mnh nh chng lin tc tip nhn nng lng t do t mi trng dng quang nng hoc ha nng v bin ha n thnh cc dng nng lng sinh hc phc v cho cc qu trnh hot ng sng. S bin ha, tch ly v s dng nng lng sinh hc xy ra song song vi s chuyn ha vt cht v tun th cc nguyn tc ca nhit ng hc. Nhng bin i nng lng t do ca h thng phn ng c k hiu bng G c gi tr l Kcal/mol. i lng ca G l hiu s gia lng nng lng t do ca trng thi cui (sau phn ng) G2 v nng lng t do ca trng thi u (trc phn ng) G1. Nu G0 (c gi tr dng), phn ng thu nhit, mun thc hin phn ng cn phi cung cp nng lng. Cc phn ng thu nhit ch c th c thc hin cng vi cc phn ng ta nhit, ngha l vic tng nng lng t do ch c th c c do cc phn ng lin hp khc tin hnh vi vic gim nng lng t do. Cc qu trnh c bn gn lin vi hot ng sng ca c th, nhiu kiu lm vic ca t bo, cc phn ng tng hp u l nhng phn ng thu nhit lun lun lin hp vi cc phn ng ta nhit. G c tnh theo cng thc:

134

G=

G 0 + RT lnK

trong G0 l s bin i nng lng t do tiu chun ca phn ng 250C khi nng ca tt c cc cht phn ng l 1 mol v p sut l 101,3 KPa (1atm), R l hng s kh, T l nhit tuyt i, K l hng s cn bng ca phn ng bng [C]c. [D]d /[A]a[B]b tc l nng ca cc cht tham gia phn ng A + B C + D; a, b, c, d l s lng phn t A, B, C, D tham gia phn ng. Trong h thng sinh hc, khi tnh gi tr G0 cn ch n pH, nng H+ l 1 mol, pH=0. Trng thi ion ha ca nhiu hp cht sinh hc b bin i khi pH thay i. V vy, thun tin cho vic tnh ton, xem trng thi chun ca pH l 7 v k hiu s thay i nng lng t do chun pH 7,0 l G0'. 8.2.2. Lin kt cao nng v vai tr ca ATP Cc lin kt ha hc gia cc nguyn t u l nhng tc nhn mang ch yu ca nng lng t do trong cc cht hu c. V vy, trong vic bin to ca cc lin kt ha hc trong phn t, mc nng lng t do ca hp cht s thay i. Xt v mt nng lng trong cc hp cht hu c c hai loi lin kt: Lin kt thng v lin kt cao nng (lin kt giu nng lng). Lin kt thng l lin kt m khi phn gii hoc to thnh n c s bin i nng lng vo khong 3 Kcal trn mt phn t gam (V d nh lin kt este); cn i vi lin kt cao nng s bin i ny ln hn nhiu t 7 12 kcal/mol. Trong cc hot ng sng ca c th sinh vt, cc qu trnh tng hp cc cht phn t ln t cc cht n gin, vn chuyn tch cc cc cht qua mng t bo, qu trnh vn ng v.v. lun i hi nng lng t do. Trong h thng sng cn c cc cht, cc h thng nhn nng lng t do t cc qu trnh ny chuyn n cho cc qu trnh khc. ATP l cht ph bin gi vai tr ny, l cht c vai tr trung tm trong trao i nng lng t bo v c th sng, l cht lin kt hoc c th ni l mt xch gia h thng s dng nng lng v h thng sn sinh ra nng lng. Trong phn t ATP c 3 gc phosphate, 1 gc kt hp vi gc ribose qua lin kt este, 2 lin kt gia 3 gc phosphate l lin kt anhydric. l cc lin kt cao nng c k hiu bng du ~ . ATP ( Adenosine Tri Phosphate) c biu th mt cch khi qut nh sau: Adenosine - P ~ P ~ P (trong P l cc gc phosphoric acid ). Khi ct t cc lin kt cao nng ny, s gii phng s nng lng ln gp hn 2 ln so vi lin kt este: ATP + H2O ADP + H3PO4 G0 = -7 Kcal/mol ( P )

135

ATP + H2O

AMP + H4P2O7 ( P ~ P )

G0 = - 8,5 Kcal/mol

Nu tip tc thy phn lin kt este ca AMP to thnh adenosine v phosphate v c, nng lng t do c gii phng ca phn ng ny thp hn nhiu. S chuyn ha tng h gia ATP v ADP c vai tr c bit quan trng trong qu trnh trao i nng lng ca h thng sng. Trong a s trng hp thng thy phosphore hoc sulphure tham gia to thnh lin kt cao nng (Bng 8.1).Bng 8.1. Mt s dng lin kt cao nng thng gp G0 ( Kcal/mol) -7 -7 - 10 1,3Diphosphoglyceric acid Aminoacyl-AMP Phosphoenol Pyruvic acid Creatin phosphate Arginin phosphate - 10,5 -7 - 12,8

Dng lin kt

Kiu lin kt - Anhydrid phosphate (pyro phosphate)

C trong cc cht ATP, GTP....... ADP, GDP.....

PO~

~O ~P

- Acyl phosphate

P

O RCO~ P

- Enol phosphate RCO~ P CH2 - Amid phosphate N~ P ( phosphoguanidin) R C NH ~ P NH - Thioeste C~S O RC~SR

Acetyl coenzyme A Acyl coenzyme A

- 8,8

136

8.3. Qu trnh oxy ha kh sinh hcC th nh ngha qu trnh oxy ha kh l qu trnh trao i in t. S oxy ha l s tch mt hay nhiu in t, ngc li s kh oxy l s thu in t. Tt c cc cht tham gia vo qu trnh oxy ha kh c th sng u c kh nng nhng hoc thu in t. chnh l kh nng oxy ha kh. Song song vi s oxy ha c s kh oxy v in t c chuyn t cht b oxy ha sang cht b kh:- 2e

V d: 2Fe

2+

+ Cl2

2Fe 3+ + 2Cl-

i lng c trng cho kh nng oxy ha kh ca mi cht gi l th nng oxy ha kh. C th tnh c th nng oxy ha kh theo cng thc sau: E'n= E'o + RTnF

ln

[dng oxy ha] [ dng kh]

(1)

Trong : En l th nng oxy ha kh ca mt cht nht nh trong nhng iu kin nht nh. E0 l th nng oxy ha kh cc iu kin tiu chun ( nng ca hai dng bng nhau) R l hng s kh, T l nhit tuyt i, F l tr s Faraday do Bng 8.2 trnh by E0, hiu in th oxy ha kh Go ca mi h. E0 v nng lng t

Th nng oxy ha kh cn dng tnh nng lng t do (Go) c gii phng ra trong qa trnh oxy ha kh theo phng trnh: Go = -nF.E'o (2) (Cc k hiu c gii thch cng thc tnh th nng oxy ha kh v lin quan n bng 8.2 trn) * Tin trnh ca s oxy ha sinh hc: S phn gii cht dinh dng v gii phng nng lng ca t bo (s d ha) c th c chia thnh 3 giai on c bn: giai on u: cc hp cht cao phn t b thy phn thnh cc cht n gin c phn t nh hn: cc glucid (tinh bt, glucogen v.v...) thnh cc

137

monosaccharid (glucose), cc protein thnh cc amino acid, cc lipid thnh cc acid bo. giai on th hai: bin nhng cht n gin thnh nhng cht 2 carbon l acetyl CoA (CH3 - COSCoA) (thiu). Acetyl CoA c coi l sn phm thoi ha ca cc cht glucid, lipid v protein. N c hnh thnh do s -oxy ha acid bo, do s oxy ha ca khong mt na s -amino acid cng nh do s oxy ha hiu kh glucose.Bng 8.2. Th nng oxy ha tiu chun ca mt s h thng Eo (volt) pH7, 30oC -0,42 -0,32 -0,10 +0,04 +0,23 +0,26 +0,29 +0,55 +0,81 +0,22 +0,14 +0,19 +0,03 +0,03 +0,26 +0,26 +1,13 -10,1 -6,4 -8,7 -1,4 -1,4 -12,0 -12,0 -52,0 3 1 1 1 E0 (volt) Go (kcal/pH7, 30oC) Phosphoryl ha ADP ATP

H thng oxy ha kh

in cc hydro 2H+/ H2 NAD+/ NADH + H+ FAD/ FADH2 Cytochrome b Fe3+/ Fe2+ Cytochrome c1 Fe3+/ Fe2+ Cytochrome c Fe3+/ Fe2+ Cytochrome a Fe3+/ Fe2+ Cytochrome a3 Fe3+/ Fe2+ in cc oxy 1/2 O2 / O2-

giai on th ba: Acetyl CoA c hnh thnh giai on th hai s b oxy ha hon ton trong chu trnh Szent-Gyrgyi-Krebs (chu trnh citrat) hnh thnh CO2, H2O v gii phng nng lng. Phn ln nng lng c gii phng ra giai on th ba ny (khong 2/3) Trong giai on th hai v th ba khong 30-40% nng lng ha hc c bin thnh nhit, hn 60% nng lng ny c s dng tng hp cc hp cht cao nng.

138

Trong chu trnh citrat, cc hydrogen tch ra s c oxy ha qua chui h hp to nn nng lng v H2O. Nng lng gii phng c tch tr cc phn t ATP. Ton b qu trnh c th c minh ha bng s trn hnh 8.3.Thc n glucid lipid

protein Amino acid

glucose

Acid bo Acetyl CoA

CO2

Chu trnh citrat ATP 1/2O2

H2NADFADCoQCytbCytc1CytcCytaCyta3 2H+ ADP+PHnh 8.3. Tin trnh oxy ha sinh hc

O H2O

8.4. Chui h hp t bo v s phosphoryl ha oxy ha8.4.1. Chui h hp t bo Chui h hp t bo l mt h thng cc enzyme xc tc vn chuyn H+ v eletron t c cht n phn t oxygen to H2O. Trong t bo, oxygen l cht oxy ha vn nng, cn cc phn t hu c khc nhau ng vai tr cht cho in t. y, in t v ion hydrogen ca phn t c cht khng chuyn trc

139

tip cho oxygen khng kh m c chuyn dn qua mt chui phc tp nhiu mt xch, bao gm cc h enzyme oxy ha kh, c th nng oxy ha kh nm trong khong gia th nng oxy ha kh ca c cht v ca oxygen. Cc h enzyme ny c sp t theo mt trt t tng dn th nng oxy ha kh to thnh mt chui, gi l chui h hp hay chui vn chuyn in t ca t bo. Vai tr ca chui h hp l oxy ha tng bc hydrogen ca c cht n H2O. C ch hot ng ca chui h hp t bo c th tm lc nh sau: Cht cho nguyn t hydrogen l NADH + H+ hoc trong mt s trng hp l FADH2. Nguyn t hydrogen s c chuyn ti h coenzyme Q (CoQ) thng qua h trung gian flavoprotein cha st v lu hunh. Tip theo hai in t ca nguyn t hydrogen c tch ra v i vo h thng vn chuyn in t theo trnh t cc cytochrome b-c1-a-cytochromeoxydase (a3), cui cng in t c chuyn cho oxygen. Nguyn t oxygen b kh ( trng thi ion ha) s kt hp vi 2H+ (proton) to ra phn t nc. Qu trnh chuyn hydrogen v in t trong chui h hp c th phn thnh 4 giai on: - Giai on 1: Thng thng hydrogen c tch t c cht bi dehydrogenase c coenzyme NAD+(hoc NADP +). Hydrogen ca c cht gn vo NAD+, c cht t dng kh chuyn thnh dng oxy ha v NAD+ t dng oxy ha bin sang dng kh. Mi c cht c mt dehydrogenase c hiu tng ng: AH2 + NAD+ A + NADH +H+ (Trong AH2 v A l c cht dng kh v dng oxy ha) NADH khng th t oxy ha