Chuong II-1 Protein 2011 TOM LUOC

CHNG II. VT LIU SINH HC 2.1.

Protein

1.Khi nim, vai tr ca proteinKhi nim:

l cc hp cht cao phn t bao gm ch yu l cc L-axit amin kt hp vi nhau qua lin kt peptitVai tr:

Hemoglobin: 64,5 kDa

Xc tc Vn ti Chuyn ng Bo v

+

Truyn xung thn kinh iu ho Kin to chng c hc D tr nng lng2

CHNG II. VT LIU SINH HC2.1.

Protein

2. Axit aminKhi nim:

l hp cht trong phn t c cha t nht mt nhm amin v mt nhm cacboxyltrong thin nhin c 150 loi AA, trong c 20 loi tham gia cu to protein = 20 a.a cu trc

Cng thc chung:

R H2N C H

COOH8

CHNG II. VT LIU SINH HC2.1.

Protein

2. Axit aminTn vit tt:

9

1a) AXIT AMIN KHNG PHN CC,mch bn l hydrocacbon k nc (1)

Cu & que

Ho lp th

Hnh chiu FischerR= Hydro Phn linh ng, mm do Khng cha ccbon bt i

A.a kiu mu Nhm R l -CH3 12

:N

:H

:O

:C

Mch bn k nc Dui thng hoc phn nhnh

Cha lu hunh = Tng tc v kt gn vi ion KL 13 Metaloprotein

Prolin: axit imin duy nhtCu trc vng: Proline b hn ch v mt hnh th, lm nh hng n cu trc protein

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1b) AXIT AMIN KHNG PHN CC,

mch bn l hydrocacbon thm

Vng phenyl hon ton k nc

Nhm hydroxyl (-OH) Hot ng

Vng Indol Nhm methylen (-CH-) 2 vng lai + Nhm NH

Tyr & Trp do c nhm -OH & -NH nn t k nc hn 15

Nhm II: Axit amin trung tnh

(5)

Alanin c hydroxyl ho

Valin c 1 nhm hydroxyl thay th cho nhm methyl

Tm bt iOH + ng =Glycoprotein OH + P = c ch, iu ho th 2

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CysteineSerine c nhm sulfhydryl, hay thiol (-SH) thay th cho nhm hydroxyl (-OH)

-SH hot ng hn OH. 2 SH = lk disulfide, bn protein

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Asparagine (Asn, N) Cc Amid cua a.a

Glutamine (Gln, Q)

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Nhm III:

Cc mch bn axit tnh (2)

Glutamate hoc axit glutamic(E, Glu) v Aspartat hoc axit aspartic (D, Asp) Lun tch in m pH sinh l(pH 7,4)

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Nhm Iv:

Cc mch bn baz tnh

Histidin (H, His) Lyzin (K, Lys) Arginin (R, Arg)

Nhn mt proton pH sinh l (tch in dng) His b ion ha gn pH sinh l; do c th hot ng nh l mt cht nhn proton hoc cho proton ph thuc vo pH ca mi trng xung quanh. (His l mt a.a c tnh baz yu)

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Cc axit amin c to thnh nh th no? Khi nim axit amin cn thit

Ngi v ng vt khng th tng hp c mt s a.a. Cc a.a ny c gi l cc a.a cn thit (a.a khng thay th): valine, isoleucine, leucine, methionine,phenylalanine,tryptophan, threonine, lysine

Arginin v Histidin l cc a.a khng thay th tr nh v mt s ngi mc cc bnh ri lon trao i cht (extreme metabolic stress disease)- y l cc axit amin khng thay th c iu kin.26

tnh cht ca axit amin(1)

Tnh quang hot

Kh nng lm quay mt phng phn cc ca nh sng

Ch tr a.a n gin nht l glyxin cn tt c cc axit amin u c cha cacbon bt i, nn chng c tnh quang hot. Hng quay ca mt phng nh sng phn cc c k hiu bng du (+): quay phi v (-): quay tri.31

(2)

Tnh cht ion ha (in ly lng tnh)

Tng in tch: +1

0

-1

33

Cc ph.ng th ca nhm -NH2:

(5) P.ng vi 1- Fluoro -2,4 dinitrobenzen( thay th 1 hidro ca nhm amin bng gc thm dinitrophenyl): 25oC, pH 7-8

SPhm thu c (DNP-aa) c mu khng b thy phn trong mi trng axit. Tnh cht ny l c s ca phng php Sanger, mt phng php dng xc nh trinh t a.a trong protein (trinh bay trong phan tinh chat cuaprotein).

43

Cc ph.ng th ca nhm -NH2:

(6) Phn ng vi HCHO: phng php chun formol ca Sorensen

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(7) P.ng vi axit nitr

Nh cc amin bc nht khc, axit amin p.ng vi axit nitr gii phng kh nit v oxy axit tng ng c hnh thnh:R H C - NH2 COOH + HO-N=O R H C - OH COOH + N2 + H2 O

Da vo lng nit thot ra ta c th tnh c lng axit amin c trong dung dch (phng php Van Slyke).

45

(8) Phn ng vi ninhydrin- Nhm cacboxyl, amin u tham gia = CO2 v NH3 u b loi:

R

H2N

C

H+

pH 5-7, toC

CO2 + NH3+ RCHO +

COOH- phn t ninhydrin kh cng vi 1 phn t ninhydrin mi, p. vi NH3b loi ra trn to thnh 1 hp cht c mu tm :

H

+ NH3+

HNH4

+ 3 H2 O

+ NH3

-Nguyn t N ca NH3 = cu ni ni 2 phn t nihydrin to thnh hp cht c mu tm 46 ; OD570 nm- Xem thm: http://www.ecompound.com/Reaction%20reference/reactions/Ninhydrin%20with%20amino%20acid%20mechanism.gif

(9) Phn ng vi reductonXem thm: SMOKING TOBACCO PRODUCT AND METHOD OF MAKING THE SAME .United States Patent 3722516

R H2N C H

+R-CO-CO-R RCHO + R-CHNH2-CO-R+CO2

COOH

(10) Phn ng ca axit amin vi ng kh (Phn ng Maillard)To hp cht c mu nu, hng thm c trng48

(11) Phn ng to lin kt peptid

49

CHNG II. VT LIU SINH HC2.1.

Protein

3. Cu trc ca protein Cu trc bc 1L trnh t sp xp ca cc axit amin trong mch polypeptideC k axit amin c k! trnh t sp xp, nhng ch 1 ng phn c hot tnh sinh hc. Lin kt tn ti trong cu trc bc 1: lin kt ng ho tr gia cc axit amin55

Cu trc bc hai: (1)xon alphaDng cu hnh l xo c sinh ra do s t cun xon ca 01 on mch polypeptide c gi bn vng nh cc lin kt hydro ni phn t, c hnh thnh gia nhm CO ca aa th i vi nhm NH ca aa th i+4.

59

Cu trc bc hai: (2) t giy xpCu trc gp np beta; Dng hnh ch chi Sinh ra nh s tng tc gia cc on mch polypeptide

c gi vng nh lin kt hydro hnh thnh gia nhm CO ca on mch polipeptide ny vi nhm NH ca on mch polypeptide gn k.

(A)

(B)62

:N

:H

:O

:C

:R

Cu trc bc ba

Cu hnh ca ton b mch polypeptideMyoglobin Ch yu l xon alpha, tng = 8 xon (75% mch chnh) Nhm ngoi kt gn vi O2 Nhm Heme l protoporphyrin IX, & nguyn t st tm71

1 loi Protein (Cro) ca thc khun th lambda Dimer ca cc di n v xc nh

Cu trc bc bn, dimer

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4) Tnh cht proteinHnh cu

4.1. Hnh dng v kch thcHnh siProtein c cu trc bc hai bn chc

V nh hnh

Protein c nhiu aa khng phn cc

Tng tc tt vi nc, to cu hnh ngu nhin

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Kch thcHt nano: 1-100 nm; 1 kDa = 1000 Dalton

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4.2. Tnh cht in li lng tnh

pI pH>pI: a anion pH