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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
14
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
18
CysteineSerine c nhm sulfhydryl, hay thiol (-SH) thay th cho nhm hydroxyl (-OH)
-SH hot ng hn OH. 2 SH = lk disulfide, bn protein
19
Asparagine (Asn, N) Cc Amid cua a.a
Glutamine (Gln, Q)
20
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)
21
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)
22
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
44
(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
74
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
78
Kch thcHt nano: 1-100 nm; 1 kDa = 1000 Dalton
79
4.2. Tnh cht in li lng tnh
pI pH>pI: a anion pH