Tieu Luan Hoa Sinh

8/3/2019 Tieu Luan Hoa Sinh

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1

LI M U

Ha sinh thc phm nghin cu v cu to, tnh cht ca cc cht to nn thc

phm v s chuyn ha ca cc cht, chuyn ha nng lng trong qu trnh bo

qun, ch bin thc phm. y l b mn quan trng, gi vai tr nn tng, c s cho

nhng mn hc chuyn ngnh.

Cng vi protein v lipid, glicid l mt hp cht hu c gi vai tr thit yu

i vi cuc sng, ph bin trong cc sn phm thc phm. Trong khu phn n hng

ngy, glucid chim t l ln nht v khi lng, cung cp phn ln nng lng gipchng ta hot ng bnh thng. K c nhng loi carbohydrate khng tiu ha c

cng c vai tr quan trng trong cn bng dinh dng.

C th thc vt l mt c my sinh hc tuyt vi tng hp nn glucid t nhng

hp cht v c ban u (CO2 ,H2O v nng lng nh sng mt tri). C th ngi,

ng vt th s dng ngun nguyn liu glucid ly t thc vt l chnh, qua qu trnh

phn gii vi c ch cht ch to ra n v c bn l glucose nguyn liu ch yu

cho hot ng sng, trung tm ca s chuyn ha.

Glucid cn to ra nhiu tnh cht chc nng quan trng cho thc phm nn tm hiu v

QU TRNH TNG HP, PHN GII GLUCID l vic lm cn thit i vi sinh

vin ngnh thc phm. N gip chng ta hiu r hn v c ch, bn cht ca s

chuyn ha, qua c nhng kin thc nht nh s gip ch rt nhiu cho vic hc

tp, nghin cu sau ny. chnh l mc ch ca nhm khi lm ti ny.


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1. Gii thiu chung v Glucid

1.1.Khi nim

Glucid l hp cht hu c kh ph bin c c th ng, thc vt v vi sinh vt. Cc

nguyn t cu to nn glucid l C, H, O. Cng thc cu to ca glucid thng c

biu din di dngCmH2nOn (m, n 3). Trong phn t glucid c cha nhm aldehide

(-CHO), cetol (-C=O). Ngoi ra cn c mt s loi glucid c bit, trong cu trc ca

chng cn c thm S, N, P.

1.2. Vai tr

1.2.1. i vi c th L sn phm trung gian ca qu trnh trao i cht. Ngun nguyn liu trc tip h hp. Ngun d tr, to nng lng. To cu trc trong c th thc vt, tham gia vo thnh phn cu to ca nhiucht quan trng nh: AND, ARN

Cung cp nng lng ch yu ( 4,13 kcal/g) Gip cho qu trnh tiu ha.1.2.2. Trong cng ngh thc phm

L cht liu c bn, cn thit v khng th thiu ca ngnh sn xut ln men. Cc sn phm nh: ru, bia, nc gii kht, m chnh, acid amin, vitamin uc to ra t ci ngun glucid.

To ra cu trc, hnh th, trang thi, cng nh cht lng cho cc sn phm thcphm.

To kt cu: To si, to mng, to gel, to c, cng, n hi cho thcphm: tinh bt, thch, pectin trong min, mt qu, kem, gi la To kt cu c th


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ca mt s loi thc phm: phng n ca bnh phng tm, to bt cho bia, xp

cho bnh m, v chua cho sa

To cht lng: to ngt cho thc phm (cc ng). Tham gia to mu sc vhng thm cho sn phm (ng trong phn ng caramen ho, melanoidin). Cctnh cht lu bin cho sn phm thc phm: dai, trong, gin, do C kh

nng gi c cc cht thm trong sn phm thc phm; to m cng nh lm gim

hot nc lm thun li cho qu trnh gia cng cng nh bo qun.

1.3. Phn loiC nhiu cch phn loi. Sau y l mt s cch phn loi:

Theo cu to: glucid c chia lm 3 nhm

Theo mc ch s dng ( ngt): ng, khng ng.

Theo mc phc tp ca phn t, ly ng n lm c s:

Loi ose: l ng khng thy phn c na.


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Loi osid: l nhng glucid phc tp do nhiu monosaccharide ghp li. Gm 2 nhmln: holosid( thy phn cho mono) v heterosid( thy phn cho mono v nhiu nhm

khng phi glucid).

Dn xut amin, phospho, dn xut dng glucocid

1.4. Tnh chtNhn chung, cc glucid t n gin n phc tp u c mt s tnh cht in

hnh ging nhau. Ta xt cc tnh cht ca monosaccharide.

1.4.1. Tnh cht vt lyKhng bay hi, tan trong nc, t tan trong ru, khng tan trong acid, dung

mi hu c.

yC hin tng solvat ha lm dung dch kh kt tinh.yTn ti trng thi h bin (mch thng v vng).yC kh nng lm quay mt phng nh sng phn cc (ph thuc vo dng

anomer, tautomer).

yKh nng ha tan ph thuc vo tng loi ng.y Tnh ht m, lm bng khc nhau tng loi ng.

1.4.2. Tnh cht ho hc

yTnh kh mnh do c nhm aldehide, cetol t do: monosaccharide chuyn thnhpolyol, cc nhm aldehide hoc cetol chuyn thnh cc nhm ru tng ng.


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yTnh oxi ha theo nhiu mc : trong iu kin oxi ha nh, cc aldose b oxiha thnh aldonic acid (xy ra trong bt nng bnh, xc xch ln men, mt s

sn phm sa). Khi dng cc acid mnh hn nh HNO3 s to thnh

dicaboxylic acid.

B oxy ha nh bi Br2:

Tc dng vi HNO3:


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Khi oxy ha bng dung dch Br2 c bo v nhm chc CHO bng metyl ha

V d t axit glucuronic s cho cht xilose l mt pentose

yTo ester vi acid.


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Khi un si cc pentose, hexose vi cc acid c nng cao nh HCl 12%, H2SO4

m c th cc phn t H2O s b mt i v to thnh cc furfurol t pentose hoc

oxymethylfurfurol t hexose. Cc sn phm ny c hnh thnh trong qu trnh ch

bin cc sn phm thc phm.

y Phn ng trong mi trng kim.Trong dung dch kim yu nh Ba(OH)2 , Ca(OH)2 c th xy ra s ng phn ha

gia glucose, fructose, mannose. Hin tng ny c th xy ra trong c th. Trong

dung dch kim long, cc monosaccharide mch thng chuyn sang mch vng.trong

mi trng kim long 370 C cc nhm endiol s chuyn vo gia mch.

Nng kim cao hoc nhit cao, cc monosaccharide c th b phn gii, hin

tng caramen hnh thnh, Cc mch cacbon d b t.


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H

C

OC

OH

H

R

COOH

C OHH

HC H

COOH

HO HC

C HH

R

+

D- Glucose

R

C

Acid metasaccharicCH3

C

C

O

O

R

COOH

C OH

R

H3C

COOH

C CH3HO

R

CH2OH

C

C

R

O

O

COOH

HOH2C C OH

R

COOH

CHO CH2OH

R

+

+

Acid saccharic

Acid isosaccharic

Phn ng vi cc loi thuc th (phenylhydrazin) dng nhn bit cc ng nkhi phn tch.

Phn ng vi phenylhydrazin, gm 3 giai on:


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Giai on 1 : s to nn phenyhdrasen:

Giai on 2 : s oxy ha nguyn t v tr cacbon th 2 to nn nhmcacbonyl:


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Giai on 3: mt phn t phenylhydrazin th ba s tham gia phn ng vinhm cacbonyl v to nn sn phm cui cng l phenylosasen ca glucose:

Tm tt phn ng gia glucose v phenylhydrazin nh sau:

ng phn quang hc Phn ng to glucozit: l mt c tnh rt quan trng ca monosaccharide. Lin ktglucosid l lin kt c bn c ngha quan trng to nn cc oligosaccharide,

polysaccharide v nhiu hp cht phi glucid khc.

Phn ng to glucozit


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Cc dng Glucozit:

R phn gluxit ca phn t glucozit , A aglucon

Tt c cc glucosid d dng b thy phn, khi lin kt glucosid b ct t v to

thnh monosaccharide tng ng. phn ng thy phn cc glucosid c xc tc bi

acid, ch trong mt s trng hp mi do kim xc tc. a s glucosid u bn vng

vi kim.

yPhn ng caramen: sn phm ph thuc vo nhit , pH, thi gian, bn chtca ngw

Sacarose, s caramen ha:


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n 185 1900C s to thnh isesacarosen:

Khi nhit cao hn s mt i 10 % nc v to thnh caramelan c muvng:

Khi mt i 14 % nc s to thnh caramelen:

V khi mt i 25% nc s to thnh caramelin. Cc sn phm caramen ha u

c v ng.

y Phn ng maillard (phn ng vi cc hp cht cha gc amine)y l phn ng nu ha phi enzyme, xy ra gia ng kh v protein, peptide, acid

amin hoc cc amine thng qua phn ng to N- glycoside v mt chui cc phn ng

k tip khc.

V c bn, phn ng ny xy ra tng t phn ng ca ng trong mi trng acid

hoc kim, tuy nhin do s c mt ca cc hp cht nitrogen ng vai tr xc tc nn

phn ng xy ra vi tc nhanh hn trong nhng iu kin mi trng n gin hn

rt nhiu. Phn ng ny rt thng gp trong thc phm.

Glucose phn ng vi acid amin to ra glucosylamine:


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H

HO

CH2OH

H

OH

H OH

H

OH H

H3C

NH2

OH

O

Amino acid

O

O

CH2OH

HOH

OH

H

HH

HO

H

H3C

NH

OH

O

CH2OH

HH

HOOH

H OH

H

OH

H3C

NH

H

OH

O

OH

OH

CH2OH

HH

H

HO

H

H3C

H

NOH

O

Glucose Glycosylamine

(mch vng)

Hop cht khng bn d bi loai nuoc Glycosylamine (dang imine)

H C O

R

H2N R1 H

OH

C NH R1

R

+

O

CH2OH

OHHO

OH

NH R 1 H

R

C N R1

H2OH2O +_

D- Glucosylamine S to thnh cc hp cht amadori t ng glucose v phn hu chng ti 1- v 3-

deoxysone:


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HC NR1R2

C OH

C

OH

HH

C

C

HC NR1R2

OH

HC

C

NR1R2

C HHO

H

H2OH2O

H2O

HC O

C O

C O

CH2

1-, 3- dyosone

H R1R2NH,

H2C

C O

H2C

C OH

CO

H, R1R2NH

H2C NR1R2

C O

C HHO

HC O

H C OH

C HHO

R1R2NH+1, 2

Glucose

3

H2C NR1R2

C OH

CHO

H2C NHR1R2

OHC

HO C HH

4

Phn ng ngng t andose to ra gc pyrazine:

CH N

H C OH

HO C H

R1

R1CHO

H

H

C

C

NH

OH

O C H

CH2HN

N

N Oxy ha

N

N+ _


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Phn ng oxi ho cc hp cht amadori:

H2C NHR

C O

CHO H

H2C NHR

OH

OH

C

C

H2C NHR

C O

C O

H2C NHR

COOH

COOH

+

Oxy ha Oxy ha

Tip theo l cc phn ng ca cc hp cht deoxyosome to ra sn phm l nhng hp

cht mch vng c cha hoc khng cha nit gp phn to nn mu sc cng nh

mi v cho cc sn phm chin nng.

1.4.3 Tnh cht cm quan

Cc ng n, ng oligo v cc ru tng ng ca chng thng c v ngt,

y l tnh cht cm quan quan trng nht. Ngoi ra, mt vi loi c v ngt ng (

D Mannose), hoc v ng (gentibiose).

Mt s ng quan trng gm saccharode, cc loi xiro t tinh bt v glucose hay

ng o, xiro glucose- fructose, ng fructose, lactose, cc sugar alcohol nh

sorbitol, mannitol, xylitol cng l nhng loi ng ngt quan trng.

Cng v ngt c nh gi bng ngng nng cm nhn ca ng hoc

bng cch so snh vi mt ng chun khc. Cht lng v cng v ngt ca

ng ph thuc vo cng thc ha hc, cu trc ca ng v cc thng s cm

nhn v khc nh nhit , pH, s c mt ca cc ng ngt hoc cc cht khng

phi ng.

Ni chung, trong qu trnh ch bin thc phm, thnh phm v nng ca cc

cht to ngt cn c iu chnh t c cm nhn cm quan tt nht.

Trong ngnh cng ngh thc phm chng ta cn quan tm ti mt s loi

monosaccharide quan trng nh: pentose, D- xilose, D- ribose, heose, D- glucose, D-

manose, D- galactose, D-fructose ; disaccharide: saccharose, maltose, lactose,


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xellobiose; trisaccharide: rafinose; polysaccharide: tinh bt, inulin, xellulose,

hemixellulose, pectin, aga- aga, dextran, glycogen, kitin.

1.5. ng dng trong cng ngh thc phmT nhng tnh cht nu trn, chng ta rt ra c ng dng ca glucid trong ngnh

cng ngh thc phm.

y Cc ng sau khi b kh thnh ru, cc dn xut ru ny c s dng thay th ng trong thc phm gim hot ca nc, chng hin tng

kt tinh, tng cng s ti hp th nc ca cc sn phm b mt nc

sorbitol c nhiu trong mt s loi qu nh l, to, mn..., maltitol c s

dng nhiu trong cng ngh thc phm.

y Cc phn ng oxi ha cho cc sn phm l thnh phn ca cc loipolysaccharide thc phm quan trng nh pectin (cht to dy, to gel cho

qu trnh ch bin thc phm)

y Trong mi trng acid, cc ng n d tham gia vo phn ng ngc tothnh cc glucosid. Cc sn phm to ra t glucose c th l disaccharide,

oligosaccharide nhng ch yu l gentibiose, isomaltose lm gim hiu sut

ca qu trnh thy phn.

y Trong mi trng kim, cc aldose v ketose b enol ha, to thnh cc endiol,thng qua cc endiol ny c hin tng isomer ha cc ng (mt ng ny

c th chuyn thnh ng khc). cc disaccharide, trng hp chuyn

lactose thnh lactulose c nghin cu s dng trong thc n ca tr s sinh

v chng c tc dng h tr tiu ha v ngn nga hin tng to bn tr.

y Khi un nng dung dch ng trong mi trng acid hoc kim, s to ra cccht c mu nu vi mi caramen c trng. Ty iu kin m phn ng xy

ra theo hng to mu hay to mi nhiu hn. Trong mt s trng hp, vidung dch m thch hp s tng kh nng to ra cc cht mi, ch yu l

dihydrofuranone, cyclopentenolone, cyclohexenolone v pyrone. Ngoi ra, un

nng xir glucose vi acid sunfuric, c mt ammonia s tng cng to ra cc

hp cht polime c mu nu. bn v kh nng ha tan ca cc hp cht ny

s tng khi c thm cc anion bisulfate.


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yPhn ng maillard: ty trng hp c th m c li hay gy hi.y Hin tng to mu nu rt cn thit trong cc sn phm chin, nng nhng

li c hi trong cc sn phm nh sa c, rau c sy, nc st c chua;

tng t, vic to ra nhiu hp cht bay hi c mi cng rt cn thit trong

qu trnh chin, nng nhng li nh hng n qu trnh bo qun, ch bin

nhit nh thanh trng, tit trng; v ng cn thit trong ch bin c ph

nhng li to ra mi l khi quay tht, c; to ra cc hp cht c tnh kh mnh

tham gia vo vic bo v thc phm khi cc phn ng oxi ha. Bn cnh ,

chng ta cn lu n kh nng lm mt i nhiu acid amin thit yu (lysine,

cystein, methionine), to ra mt s cht gy ung th,

y hn ch phn ng ny chng ta c th gim pH, gi thc phm nhit thp nht c th, trnh vng hot nc nguy him trong thi gian bo qun

v ch bin, khng s dng ng kh v thm cc gc sulfite vo thc phm.

y Ester ca sorbitol v saccharose vi cc acid bo c nhiu ng dng rng ritrong cng nghip ch bin thc phm.

y Cyclodextrin khng ht m, ngt nh, c s dng gi hng, bo v ccvitamin v cc cht d b oxi ha, giu i cc v ng cht hay cc mi khng

mong mun.

y Nhng iu trn ch mang tnh cht tng hp, khi qut v mt s c imquan trng ca glucid i vi ngnh cng ngh thc phm. bn cnh , chng

cn c rt nhiu ng dng trong cc lnh vc khc m chng ti khng cp

n.

2. Qu trnh tng hp gluxid

2.1. Tng hp cc Gluxid n gin (Quang hp Chu trnh canvil):

2.1.1.K

hi nim:Quang hp l qu trnh cy xanh v mt s sinh vt nh vi khun lu hunh, vi khun

lam, mt vi loi ng vt nguyn sinh, hp th nng lng ca lng t nh sng

bin i thnh nng lng ha hc, gii phng oxy ca nc, kh CO 2 thnh cc cht

hu c.


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2.1.2. C ch quang hp: gm 2 pha l pha sng v pha ti.

2.1.2.1. Pha sng:

Pha sng quang hp bao gm cc phn ng u tin k t lc sc t hp th nng

lng nh sng, sau d tr n trong cu trc phn t sc t di dng nng lngin t kch thch, n cc qu trnh di tr nng lng vo trung tm phn ng v cui

cng t y nng lng c bin i thnh th nng ha hc.

Pha sng quang hp gm 2 giai on:

- Quang vt l

- Quang ha hc.

a/. Giai on quang l:

- Giai on quang l ca quang hp bao gm qu trnh hp th nng lng v s di tr

tm thi nng lng trong cu trc ca phn t chlorophyll.

- Cy xanh c chiu sng, nng lng di dng cc photon p vo chlorophyl

hay carotenoit, kch hot in t cc sc t n mc nng lng cao hn nhng khng

bn, cc in t tr v mc nng lng ban u, ng thi nng lng ca lng t

nh sng c truyn cho phn t sc t khc. Qu trnh truyn photon din ra cho

n khi cc photon p vo trung tm phn ng c chlorophyll a chuyn bit, kch

hot in t ca trung tm phn ng ln mc nng lng cao trung tm phn ng

trng thi kch thch.

- Ngoi phn t chlorophyll, trung tm phn ng cn cha cc sc t ph

carotenoitv..v Cc sc t khc nhau s hp thu tt cc bc sng khc nhau ca

quang ph, truyn in t v hidro b kch thch cho dip lc a trc tip tham gia cc

phn ng sng.

b/. Giai on quang ha:- Pha sng thc hin nh tc ng tng h ca 2 h thng quang ha I v II (HTQH).

HTQH l phc hp thu nhn nh sng vo trung tm phn ng gm cc sc t

chlorophyll a,b,c,d v carotenoit.

- Trung tm phn ng (TTP) l cc phn t chlorophyll chuyn bit gm:


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Trung tm phn ng I c kh nng hp thu nng lng nh sng bc sng di( > 730nm). H sc t I gm carotenoic, chlorophyll b, chlorophyll a- 660,

chlorophyll a-670, chlorophyll a-678, chlorophyll a-683, chlorophyll a-690 tham gia

vo hot ng hp th nng lng nh sng h I v truyn nng lng n trung tm

quang hp I (chlorophyll- P700). T P700 thc hin chui vn chuyn e-

quang hp nh h quang ho I to ATP v

NADPH2. H vn chuyn in t b6, xytocrom F.

Trung tm phn ng II c kh nng hp thu nng lng nh sng c bc sngngn hn h nh sng I ( < 700nm). H sc t II gm c xantophyll, chlorophyll b,

chlorophyll a-680, chlorophyll a-660, chlorophylla-670 ... tip nhn nh sng h II ri

truyn nng lng cho trung tm phn ng II (P680 hay P690). T trung tm quang

hp II in t c truyn qua h quang ho II l quinon, plastoquinon, xytocrom

b559 sang tm quang hp I (P700). c bit tham gia vo hot ng ca trung tm

quang hp II c H2O vi s quang phn ly nc s cung cp H+ v e- cho qu trnh

photphoryl ho v tng hp NADPH2.

Mi quan h gia 2 tm quang hp c thc hin qua s sau:


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- Nng lng in t khng c truyn tip tc nh trong phc hp thu nhn nh

sng, bin i theo con ng quang phosphoryl ha vng v khng vng

Quang phosphoryl ha khng vng: L c ch thu nhn truyn nng lng in tt HTQH II n HTQH I, km theo s bin i nng lng in t thnh nng lng

ha hc di dng ATP, to NADPH gii phng oxy.

Quang phosphoryl ha vng: l qu trnh bin i nng lng ca lng t nhsng thnh nng lng ha hc, tch ly trong lin kt cao nng ATP. Qu trnh din

ra trong chui vn chuyn in t.

- Nng lng ca lng t nh sng c truyn trong HTQH II, kch hot P680

thnh trng thi kch thch P680*. Cp in t ca P680* c nng ln mc nng

lng cao v truyn qua h thng pheophytin (ph), plastoquinon (Q) A v B, bin i


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Q thnh dng kh (QH2). P680* tr thnh gc cation, l cht oxy ha mnh c i lc

ln vi in t, ginh in t ca nc v tr v mc nng lng ban u P680. Phn

ng quang phn ly nc din ra cng vi s gii phng oxy.

Theo phng trnh sau:

Chlorophyll, enzym, h

2 H2O 4 H+ + O2

+ Nng lng nh sng gy cm ng vn chuyn nc n plastoquinon (Q), bin

i thnh dng kh QH2, gii phng oxy.

Chlorophyll, enzym, h

2Q + H2O O2 + QH2

+ Cp in t ca QH2 c th nng cao truyn qua phc hp Cyt b, f plastocyanin n

HTQH I kch hot P 700 thnh dng P700* kch thch. Sau in t c truyn qua

chui vn chuyn in t n feredoxin. Feredoxin l cht kh mnh, di tc dng

ca feredoxin NADP+ reductase xc tc cho phn ng to thnh NADPH. Qu trnh

vn chuyn nng lng in t trong h thng quang ha II v to nn chnh lch

proton dn n tng hp ATP.

Ktqu chung ca pha sng l:

12H2O +18ADP +18H3PO4+12NADP + 18ATP + 12NADPH2 + 6O2 + 18H2O

Pha sng to ra ATP v NADPH2 cung cp cho pha ti quang hp.

2.1.2.2. Pha ti (chu trnh Calvin Benson):

- Sau khi pha sng to ra ATP v NADPH2 giai on tip theo ca quang hp l s

dng ATP, NADPH2 tng hp nn cc cht hu c t CO2, l qu trnh ng

ho CO2. Qu trnh ng ho CO2 l mt chui cc phn ng ho sinh nh cc enzim

xc tc.

- Qu trnh ny ch s dng sn phm ca nh sng to ra trong pha sng l ATP,

NADPH2 dng lm nng lng v lc kh m khng dng trc tip nng lng nh

sng nn c gi l phn ng ti, pha ti.

Cc giai on ca pha ti gm:


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- Giai on 1: Giai on c nh CO2 vi ribulose- 1,5 diphosphat to thnh 1 phn t

ng 6C khng bn, sau thy phn thnh 2 phn t ng 3C. Phn ng c s

xc tc ca enzym ribulose- 1,5 diphosphat cacboxylase

6C5 + 6CO2 + 6H2O 12C3(APG)

-Giai on 2: giai on kh APG

12APG + 12ATP + 12NADPH2 12C3(AlPG) + 12ADP + 12H3PO4 + 12NADP

- Giai on 3: ti sinh Ribulose- 1,5 diphosphat

10C3 + 6ATP + 4H2O 6C5 + 6ADP + 6H3PO4

2C3 + 2H2O C6H12O6 + 2H3PO4

- Cc phn ng ph trong pha ti:

Phn ngthy phn:

phosphatase

Sedoheptulose-1,7-diphosphat Sedoheptulose-7-diphosphat

Phn ng ng phn ha:

phosphopentoseepimerase

Xylulose- 5- phosphat Ribose- 5 phosphatphosphopentoseisomerase

Ribose- 5- phosphat Ribulose- 5- phosphate

- Phn ng cui cng ca pha ti: phn ng phosphoryl ha.

phosphoribulosekinase

Ribulose- 5- phosphat Ribulose-1,5- diphosphatATP ADP+ H+

Kt qu chung ca chu trnh:

6CO2 + 12H2O + 12ATP + 12NADPH2 C6H12O6 + 12NADP + 18ADP +

18H3PO4


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Tm tt phn ng ca pha ti theo s sau:

Chu trnh Calvin

Kthp vi pha sngta c:

18ADP + 18H3PO4 + 12NADP 6H2O + 18ATP + 12NADPH2 + CO2

6CO2 + 12H2O + 18ATP + 12NADPH2 C6H12O6 + 12NADP + 18ADP +

18H3PO4 + O2

AS

Sc t

6CO2 + 6H2O C6H12O6 + O2

Sn phm chu trnh Calvin l C6H12O6, t C6H12O6 s to nn tinh bt, cc hp cht

hu c khc. C th ni mi cht hu c c trong cy u c to ra t quang hp.

2.2. Tng hp Oligosaccharide


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Qu trnh tng hp saccharose v lactose :

- Tng hp saccharose: Nguyn liu tng hp l glucose dng hot ho l UDP-

glucose; fructose -6-P vi s tham gia ca enzym synthetase (E1) v

phosphatase theo phn ng sau :

E1

UDP- glucose + Fructose UDP + saccharose -6-P.

Phosphatase

Saccha rose -6-P + H2O Saccha rose + H3PO4.

- Tng hp lactose: Lactose c tng hp di tc dng xc tc ca

lactosesynthetase (E2 )

E2

UDP-galactose + D- glucose Lactose +UDP.

2.3. Tng hp Polysaccharide:

2.3.1. Tng hp tinh bt:

- Tng hp amylose:

+ Nguyn liu tng hp l glucose dng hot ha, l ADP-glucose v UDP-

glucose.

+ Tng hp ADP-glucose t glucose-1-Phosphat di tc dng ca ADP-

glucosepyrophosphorylase(E3).

+ ADP-glucose l hp cht cao nng, nng lng ca lin kt cao nng cung cp cho

phn ng ko di chui.

+ Phn ng cn cht mi (1,4)- poliglucose c khong 4 gc glucose. Cht mi nhn

glucose di tc dng xc tc ca amylosesynthetase (E4).

E4

Cht mi + ADP-glucose (Cht mi)n+1


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=> Tng hp gluxid l mt qu trnh khng th thiu v c nhiu vai tr quan trng

trong cc c th sng nh tng hp cht hu c; tch tr, vn chuyn nng lng (nh

starch, glycogen) v cc thnh phn cu trc (nh cellulose trong thc vt v chitin

trong ng vt); tng tc gin tip gia cc t bo v gia cc t bo vi cc thnh

phn khc trong mi trng ca t bo, to ra nng lng nui sng mi sinh vt trn

Tri t; b p li nhng cht hu c tiu hao trong qu trnh sng.

3. Qu trnh phn gii monosaccharide

3.1. Phn gii monosaccacharide

Bn cht ca s phn gii monosaccharide trong t bo l s b gy dn dn mch

cacbon cho ti sn phm cui cng l CO2 v H2O, ng thi nng lng ha hc

trong cc lin kt ca nguyn liu h hp c chuyn thnh nng lng rt d s

dng tch ly trong cc phn t ATP.

3.1.1. ng phn

ng phn l giai on u tin ca qu trnh phn gii glucose xy ra khng cn s

hin din ca O2. ng phn xy ra trong dch t bo cht ca tt c t bo sng, v

l chui phn ng xy ra nhng sinh vt u tin khi m tri t cn cha c O2

Glucose l mt hp cht bn vng, t c xu hng phn ct ra thnh nhng cht ngin hn, do t bo mun ly nng lng t glucose trc tin phi u t cho n

mt t nng lng hot ha phn t. Do , giai on u ca ng phn l cung

cp ATP cho phn t glucose (Hnh 1). Trong cc phn ng chun b hai phn t ATP

gn gc phosphat cui cng ca n vo phn t.


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Hnh 1. Cc phn ng chnh ca ng phn

Trong phn ng ny hexokinase xc tc chuyn mt gc phosphat vo glucose.

Kinase l tn chung c dng cho cc enzyme xc tc chuyn gc phosphate t

ATP cho cc cht nhn, lp ph ca transferase . Hexokinase khng nhng xc tc s


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phosphoryl ha glucose m cn xc tc s phosphoryl ha cc hexose khc nh

fructose, manose.

Phn ng k tip l phn ng chuyn i glucose-6-phosphat thnh fructose-6-

phosphat.

Sau khi to ra sn phm trong bc (2), mt phn t ATP na c tiu th thm

mt gc phosphat na vo phn t.

K tip fructose-1,6-bisphosphat b ct i gia C th ba v C th t to ra

hai cht 3C tng t nhau trong bc (4). Mt cht l PGAL (phosphoglyceraldehyd)

v mt cht trung gian thng chuyn i ngay thnh PGAL trong bc (5). PGAL l

mt ng trung gian 3C, l cha kha trung gian trong c qu trnh ng phn v

quang hp.

n giai on ny qu trnh ng phn s dng 2 phn t ATP.

Phn ng k tip dn n s thnh lp ATP mi, tht s l hai phn ng. Phn

ng u l mt phn ng oxy ha kh: hai in t v mt ion H+ c ly t mi

phn t PGAL (nh vy phn t ny b oxy ha) bi phn t nhn in t NAD+

(nicotinamid adenin dinucleotid), cht ny b kh. NAD+ rt gn vi NADP+ tmthy trong lc lp. Trong trng hp ny sn phm trung gian l NADH thay v l

NADPH.


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Phn ng th hai l s phosphoryl ha PGAL. Nng lng c gii phng t

s oxy ha PGAL c dng gn mt gc phosphat v c P vo PGAL, gc

phosphat c gn vo bng mt cu ni giu nng lng.

Trong phn ng k tip, gc phosphat mi c chuyn vo ADP to ra

ATP. Trong qu trnh ny, mt gc phosphat giu nng lng c chuyn vo mt

c cht ADP to thnh ATP, phn ng ny c gi l phosphoryl ha mc

c cht (substrate-level phosphorylation). Sn phm 3C l PGA, mt cht trung

gian trong chu trnh Calvin-Benson, mt ln na cho thy s tng quan gia hai qutrnh:

giai on ny, t bo thu li c 2 phn t ATP dng cho s phosphoryl

ha glucose trong lc bt u ng phn. Nng lng u t ban u c tr

li. Qua phn ng k tip, cui cng l nc c tch ra t PGA, v sau gc

phosphat c chuyn i v c gn li bi cu ni giu nng lng:

Sau phn ng sp xp li trong bc (9) gc phosphat c chuyn vo ADP

theo s phosphoryl ha mc c cht thnh lp ATP, kt qu to ra hai phn t

ATP v hai phn t acidpyruvic:

V hai phn t ATP s dng trong bc (1 v 3) c ly li trong bc (7), nn

hai phn t ATP ny l c tng hp thm cho t bo.

Cc im quan trng cn ch trong s ng phn l:


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- Mi phn t glucose (C6H12O6) b phn tch thnh hai phn t acid pyruvic

(C3H4O3).

- Hai phn t ATP s dng trong lc u ca qu trnh, sau c bn phn t

c to ra, nh vy t bo cn c hai phn t ny.

- Hai phn t NADH c thnh lp.

- V khng s dng oxy, qu trnh c th xy ra d c s hin din ca O2 hay

khng.

- Cc phn ng ca ng phn xy ra trong dch t bo cht ca t bo, bn

ngoi ty th.

3.1.2. S ln men

Trong ng phn, hai phn t NAD+ c kh thnh NADH. Chc nng ca phn

t NAD+ trong t bo l vn chuyn in t, trao i ion H+ v in t gia cht ny

v cht khc. Do , NAD+ ch l mt cht tm thi ti ion H+ v in t, sau khi

chuyn ion H+ v in t cho cht khc th n tr li lm cht ti tip tc. Nu

NADH c thnh lp khng nhanh chng loi b ion H+ v in t th NAD+ trong

t bo s thiu; khi bc (6) trong ng phn khng th xy ra v qu trnh ng

phn tm dng li. Nh vy, s oxy ha NADH thnh NAD+ l cn thit cho qu

trnh ng phn tip tc.

Trong hu ht t bo, nu c O2, n s l cht nhn in t cui cng t

NADH. Nhng di iu kin ym kh, khng c O2 nhn hydro v in t th

acid pyruvic c to ra trong qu trnh ng phn s nhn hydro v in t t

NADH, qu trnh ny c gi l s ln men.


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Hnh 2. Cc phn ng chnh ca s ln men

t bo ng vt v nhiu vi sinh vt s kh acid pyruvic to ra acid

lactic:

hu ht t bo thc vt v men (yeast), sn phm ln men l ru ethyl v CO2, qu

trnh ny c p dng trong sn

xut


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V vy, trong iu kin ym kh, NAD+ nh con thoi i qua i li gia bc

(6) v bc (11), ly hydro v in t to ra NADH trong bc (6) v tr li hydro

v in t trong bc (11).

S ln men l s ni tip ca qu trnh ng phn, bng cch ny glucose c bin

i thnh ru hay thnh acid lactic di iu kin ym kh, s ln men s dng mt

phn nng lng rt nh t glucose, sn phm l cc cht cn cha rt nhiu nng

lng t do.

S ln men ca nhng t bo men v nhng vi sinh vt c ng dng trong

nhiu k ngh quan trng nh lm bnh m, phomat, yogurt, sn xut ru v cc loi

thc ung c ru; mt s sn phm khc c to ra t cc vi sinh vt khc nh mi

c trng ca phomat Thy S l do sn phm ln men l acid proprionic.

3.1.3. S oxi ha acidpyruvic

Nu c s hin din ca O2, th O2 l cht nhn in t cui cng t NADH, do

acid piruvic s c a vo ty th v y s c tip tc bin dng v ng thi

to ra nhiu ATP mi.

Acid pyruvic trong dch t bo cht c chuyn vo ngn trong ca ty th. Qua mt

chui phn ng phc tp, acid pyruvic b oxy ha thnh CO2 v mt gc acetyl 2C,

cht ny gn vi mt coenzym c gi l coenzym A (CoA) to ra cht acetyl-CoA. Khi acid pyruvic c oxy ha, in t v ion H+ b ly i, v NAD+ li l cht

nhn in t v ion H+ to ra NADH. Chui phn ng phc tp ny c th c

tm tt trong phng trnh sau:

Cui giai on II, 2 trong 6C ca glucose ban u c gii phng ra di

dng CO2

3.1.4. Chu trnh Krebs

Chu trnh Krebs l mt chui cc phn ng ha hc xc tc bi enzym, c vai

tr quan trng bc nht trong mi t bo sng c dng xy trong h hp t bo. Cc


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thnh phn v cc phn ng trong chu trnh axit Kreps c Albert Szent-

Gyrgyi v Hans Krebs tm ra.

Chu trnh Kreps to ra ATP cung cp nng lng cho mi hot ng sng

ca t bo, cng nh cho mi hot ng ca c th. N ly nguyn liu t qu trnhng phn ca glucose v din ra ti cht nn ca ti th.

- Nguyn liu l Acid piruvic ( CH3COCOOH) s sinh ra 2 NADH, 2ATP , 2Acetyl CoA

- 2 Acetyl CoA ny i vo chu trnh Krebs s sinh ra 4CO2 , 6 NADH, 2 FADH2Acetyl-CoA cung cp cho phc hp ca hng lot phn ng ha hc ni tip nhau

theo vng trn khp kn gi l chu trnh citric acid ca Krebs

c im:

- Cn gi l chu trnh Citric Acid hoc chu trnh Tricarboxylic Acid (TCA)- Chu trnh c 8 giai on- Phng trnh tng qut:Acetyl CoA + 3 H2O + 3 NAD+ + FAD + ADP + Pi

2 CO2 + 3 NADH + 3 H+ + FADH2 + CoASH + ATP + H2O

Cc giai on ca chu trnh Kreps:

Giai on 1:

Enzym Citrate synthase xc tc gn acetyl CoA v oxaloacetate hnh thnh citrate.

Giai on 2:


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Aconitase chuyn 3 alcohol citrate thnh 2 alcohol isocitrate to iu kin thun li

cho s oxy ha nhm hydroxyl giai on k tip.

Giai on 3:

y Qu trnh decacboxy ha oxy ha isocitrate c xc tc bi enzym isocitratedehydrogenase. Ketoglutarate c th c s dng tng hp amino acids.

- Giai on 4:


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- Enzym -ketoglutarate dehydrogenase xc tc qu trnh decacboxy ha oxyha -ketoglutarate

- Succinyl-CoA c lin kt thioester nng lng cao.y Giai on 5

- Succinyl-CoA synthetase (succinyl thiokinase) xc tc hnh thnh succinate tsuccinyl-CoA.

- ng vt, nng lng t s thy phn lin kt thioester c s dng toGTP.

- GTP chuyn nhm Pi cho ADP hnh thnh ATP (Photphoryl ha c cht)y Giai on 6

- Succinate dehydrogenase xc tc hnh thnh fumarate t succinate.- Hnh thnh lin kt C=C mt nhiu nng lng hn C=O; do , khng

nng lng to ra NAD+.

y Giai on 7


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- Hydrat ha fumarate hnh thnh malate c xc tc bi enzym fumaratehydratase.

y Giai on 8

- Qu trnh oxy ha malate hnh thnh oxaloacetate c xc tc bi enzymmalate dehydrogenase.

- OAA c s dng bt u chu trnh k tip.Kt qu : 1 phn t axtyl-coenzym A s b oxi ho hon hon to ra 3 phn t NADH,

1 phn t ATP, 1 phn t FADH2 (Flavin anin inucltit), 2 phn t CO2.

So snh qu trnh ng phn v chu trnh Kreps


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3.1.5. Chu trnh pentose phosphate

L s phn gii trc tip glucose 6 Phosphate khng qua qu trnh ng phn, gm 2

giai on oxy ha v ti to hexose phosphate.

Pentose phosphate (hexose monophosphate) gy ra s oxy ha v s kh carboxyl haC1 ca glucose 6 Phosphate, kh NADP+ thnh NADPH v pentose phosphate.

NADPH cn cho cc phn ng sinh tng hp v pentose phosphate cn cho s tng

hp nucleotid v nucleic acid.

Pha th nht ca pentose phosphate l qa trnh oxy ha glucose 6 Phosphate to

ribulose 5 phosphate v kh NADP+ thnh NADPH. Pha th hai (nonoxidative)

chuyn ha pentose phosphate thnh glucose 6 Phosphate v bt u chu trnh tr li.

3.2. Phn gii Disaccharide v Polysaccharide

3.2.1. Sthy phn

S thy phn nh phn gii tinh bt thnh glucose, maltose hay dextrin ty

thuc vo tnh cht ca enzyme:

-amylase -amylase -amylase

- ct lin kt -D-

glucosidic 1,4 c kh

nng ct khong gia

- sn phm dextrin l

ch yu

=> gi l enzym dch

ha

- ct lin kt 1,4. Bt

u t u khng kh

ct 2 gc

- sn phm ch yu l

maltose (ngoi ra cn

c glucose, dextrin)

=> gi l emzym

ng ha

- c tng hp t vi sinh vt

- c kh nng ct lin kt 1,4

v kh s phn nhnh

- ct dy ni 1,6 trong

amylopectin v glycogen, t

u khng kh ct 1 gc 1

- sn phm ch yu l glucose

(ngoi ra cn c mantose,

dextrin)

Cc polysaccharide b thy phn bi cc enzyme tng ng khc nh cellulose l

cellulase, pectin l pectinase,...


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Vi cc disaccharide s b phn gii thnh cc monose nh cc enzyme tng ng

nh sucrose bi sucrase to thnh glucose v fructose, maltose bi maltase to

thnh 2 phn t glucose...

3.2.2. Qu trnh phosphoryl- phn (phosphorolysis)

Qu trnh phosphoryl- phn l qu trnh to glucose-1-phosphate (G1P) nh enzyme

phosphorylase (glycogen phosphorylase hay phosphorylase tinh bt) vi s hin din

ca ion phosphate. Phosphoryl- phn khc vi s thy phn lin kt glucosidic l nng

lng gii phng c dng cho s to lin kt ester trong glucose-1-P (Hnh 1)

Hnh 1. S phosphoryl-phn to glucose-1-phosphate

Enzyme phosphorylase c coenzyme Pyridoxal phosphate, nhm phosphate tn cng

nh cht xc tc acid, tn cng lin kt glucosidic bng Pi . Phosphorylase tn cng

vo u khng kh ca glycogen (hay amylopectin) n khi cch ch phn nhnh 4

n v glucose th ngng li. Chng s hat ng tr li sau khi enzyme -amylase

thc hin chc nng transferase v glucosidase.


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Hnh 2: S phn gii glycogen bng glycogen phosphorylase

Cc disaccharide cng c th b phosphoryl-phn (phosphorolysis) bi enzyme

tng ng to ra mt dn xut phosphate ca monose ng thi gii phng monose

th hai. V d maltose phosphorylase chuyn ho maltose thnh glucose-1-P v

glucose.


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KT LUN

Qua nhng iu trnh by trn, chng ta nhn thy vai tr ca glucid rt

quan trng i vi ngnh cng ngh thc phm ni ring v cuc sng ni chung, v

ngy cng c nhiu ng dng hn na. Chng ta c th ngh ti mt ngy khng xa,

s c nhng loi thc phm mang hng v, mu sc hp dn, m bo cc tiu chun

v v sinh, dinh dng c ngun gc t thc vt.

T nhng con ng tng hp glucid, tng rng ch l s b n ca t nhin

nhng c trnh by kh r rng, chi tit cc cng trnh nghin cu. Qua tmhiu, chng em hiu hn v c ch ca cc phn ng phc tp, nhng rt nhp

nhng ny; v vai tr, nh hng mang tnh quyt nh ca cc enzyme ti kt qu ca

c qu trnh- to ra cc pentose, polysaccharide m bo cho sinh vt c th thc hin

trao i glucid mt cch hon ho.

Qu trnh phn gii cung cp nng lng ch yu cho mi hot ng sng ca c

th. S phn gii glucid (ng) c th c tin hnh theo nhiu con ng khc

nhau (ng phn, chu trnh krebs, chu trnh pentosephosphat), cc kiu ny b sungcho nhau v c th cng xy ra song song, hay mt vi kiu chim u th nhng

iu kin nht nh.

Tm li, tt c cc qu trnh phn gii, tng hp, chuyn ha glucid u c mi

quan h cht ch v l mt phn khng th thiu trong i sng ca cc sinh vt; to

nn ngun nguyn liu phong ph cho ngnh cng ngh thc phm.


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TI LIU THAM KHO

Ha sinh cng nghip_ L Ngc T (ch bin), NXB Khoa hc k thut H Ni.Ha hc thc phm _ Hong Kim Anh, NXB Khoa hc k thut, nm 2008.Ha hc thc phm_ L Ngc T (ch bin), NXB Khoa hc k thut H Ni, nm1994.

Ha sinh_ Nguyn Hu Chn (ch bin), NXB Y hc, nm 2001.Website tham kho: www.tailieu.vn

www.baigiang.violet.com

www.wikipedia.com

www.thuviensinhhoc.com

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