acides aminés 1

Universit DOranFacult de Mdecine et de

chirurgie dentaire

- Cours de Biochimie -

Dr. Nachi Mourad.Anne Universitaire 2010-2011

PROTEINES

ACIDES AMINES

Objectifs dapprentissage

tudier la structure des acides amins.

tudier la forme ionique des acides amins.

Comprendre les proprits physicochimiques des acides amins.

Les acides amins, lments de construction des protines

La base de la diversit des protines partir de 20 acides amins

Capacit de polymrisation.

Caractristique acido-basique.

Varit des chanes latrales.

Chiralit des molcules.

Les proteines sont une classe de molcules biologiques macromolcules de premire importance (du grec proteios).

100 000 protines diffrentes chez lhomme.

Linformation pour fabriquer ces protines est contenue dans le gnome.

Les protines sont des polymres dacides amines.La squence en acide amins dtermine la structure primaire

de la protine

Elles sont impliques aussi bien dans les structures des organismes eucaryotes, protocaryotes et viraux, que dans leur fonctionnement ( enzymes, transport, anticorps).

INTRODUCTION

Structure gnrale dun acide amin

Fonction carboxylique

Fonction amine

Chane latrale

H3N C H

R

C

O O

Structure gnrale des -acides amins

Structure gnrale thorique:

N existe pas en ralit

Forme zwitterionique: prsente

aux valeurs de pH physiologique

ACIDES AMINES - PROTEINES

C

COOH

+H3N H

RA pH faible cette forme protone de lacide aminest prpondrante.

CLASSIFICATION

. Les acides amins sont en gnral classs d'aprs les proprits

de la chane latrale en quatre groupes : acide, basique, hydrophile

(polaire) et hydrophobe (apolaire).

Symbole Code 3 lettres Nom

A Ala Alanine

C Cys Cystine

D Asp Aspartate

E Glu Glutamate

F Phe Phnylalanine

G Gly Glycine

H His Histidine

Vingt acides amins diffrents ont t identifis dans les protines, ce sont les acides amins standards.

I Ile Isoleucine

K Lys Lysine

L Leu Leucine

M Met Mthionine

N Asn Asparagine

P Pro Proline

Q Gln Glutamine

R Arg Arginine

S Ser Srine

T Thr Thronine

V Val Valine

W Trp Tryptophane

Y Tyr Tyrosine

+H3N-CH-COOH

CH3CH3-C-SH

-mercaptovaline

(pnicillamine)

+H3N-CH-COOH

CH3H-C-COOH

acide -mthylaspartique

+H3N-CH-COOH

CH3CH2CH2

norvaline

+H3N-CH-COOH

CH3CH2CH2CH2

norleucine

+H3N-CH-COOH

NH3+

CH2CH2CH2

ornithine

+H3N-CH2-CH2-COOH

-alanine

CH3-NH-CH2-COOH

sarcosine

+H3N-CH-COOH

COOH

CH2CH2CH2

acide -aminoadipique

CH3-NH-CH-COOH

CH3CH-CH3CH2

N-mthyl-leucine N-mthyl-phnylalanine

CH3-NH-CH-COOHCH2

+H3N-CH-COOH

CH3CH-CH3

-hydroxyleucine

H-C-OH

+H3N-CH-COOH

+H3N-CH-COOH

CH2S

CH2

lanthionine

phnylglycine

+H3N-CH-COOH

acide pipcolique

COOHNH

acide 4-ctopipcolique

COOHNH

O

+H3N-CH-COOH

CH3CH3-C-SH

-mercaptovaline

(pnicillamine)

+H3N-CH-COOH

CH3CH3-C-SH

-mercaptovaline

(pnicillamine)

+H3N-CH-COOH

CH3H-C-COOH


+H3N-CH-COOH

CH3H-C-COOH


+H3N-CH-COOH

CH3CH2CH2

norvaline

+H3N-CH-COOH

CH3CH2CH2

+H3N-CH-COOH

CH3CH2CH2

norvaline

+H3N-CH-COOH

CH3CH2CH2CH2

norleucine

+H3N-CH-COOH

CH3CH2CH2CH2

norleucine

+H3N-CH-COOH

NH3+

CH2CH2CH2

ornithine

+H3N-CH-COOH

NH3+

CH2CH2CH2

ornithine

+H3N-CH2-CH2-COOH

-alanine

+H3N-CH2-CH2-COOH

-alanine

CH3-NH-CH2-COOH

sarcosine

CH3-NH-CH2-COOH

sarcosine

+H3N-CH-COOH

COOH

CH2CH2CH2


+H3N-CH-COOH

COOH

CH2CH2CH2


CH3-NH-CH-COOH

CH3CH-CH3CH2

N-mthyl-leucine

CH3-NH-CH-COOH

CH3CH-CH3CH2

N-mthyl-leucine N-mthyl-phnylalanine

CH3-NH-CH-COOHCH2

N-mthyl-phnylalanine

CH3-NH-CH-COOHCH2

+H3N-CH-COOH

CH3CH-CH3

-hydroxyleucine

H-C-OH+H3N-CH-COOH

CH3CH-CH3

-hydroxyleucine

H-C-OH

+H3N-CH-COOH

+H3N-CH-COOH

CH2S

CH2

lanthionine

+H3N-CH-COOH

+H3N-CH-COOH

CH2S

CH2

lanthionine

phnylglycine

+H3N-CH-COOH

phnylglycine

+H3N-CH-COOH

acide pipcolique

COOHNH

acide pipcolique

COOHNH


COOHNH

O


COOHNH

O

On retrouve dans la nature des acides amins (400) aux structures

beaucoup plus varies mais qui ne sont pas incorpors dans des

protines.

Acides amins carbone oxygne hydrogne azote soufre

H

N

C

C

O

H

O=

H-

H-

-H

-R

Chane latrale RLacide amin est la brique de base des protines

GLY ALA VAL LEU ILE PRO

SER THR CYS MET ASN GLN

PHE TYR TRP LYS

ARG HIS ASP GLU

non-polaire polaire non charg basique acide

R

N

CO

O

+carbone

asymtrique


H

N

C

C

O

H

O=

H-

H-

-H-H

Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


glycine (G)

Lacide amin est la brique de base des protines

+

ACIDE AMINE A CHAINE AIPHATIQUE HYDROCARBONEE LINEAIRE.


H

N

C

C

O

H

O=

H-

H-

-H-CH3

Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


alanine (A)


+

ACIDE AMINE A CHAINE AIPHATIQUE HYDROCARBONEE ET LINEAIRE.


H

N

C

C

O

H

O=

H-

H-

-H-CH-CH3

Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


valine (V)

CH3

acide amin essentiel


+

ACIDE AMINE A CHAINE ALIPHATIQUE HYDROCARBONEE ET RAMIFIEE.


H

N

C

C

O

H

O=

H-

H-

-H

-CH2-CH-CH3

Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


leucine (L)

CH3



+



H

N

C

C

O

H

O=

H-

H-

-H-CH-CH2-CH3

Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


isoleucine (I)

CH3



+

carbone

asymtrique



H

N

C

C

O

H

O=

H-

H-

-H

-CH2-OH

Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


srine (S)


+

ACIDE AMINE A CHAINE ALIPHATIQUE ET A FONCTION ALCOOL.


H

N

C

C

O

H

O=

H-

H-

-H

-CH-OH

Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


thronine (T)

CH3



+

carbone

asymtrique

ACIDE AMINE A CHAINE ALIPHATIQUE ET A FONCTION ALCOOL.


H

N

C

C

O

H

O=

H-

H-

-H

-CH2-SH

Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


cystine (C)


+

ACIDE AMINE A CHAINE ALIPHATIQUE ET A FONCTION SOUFRE.


H

N

C

C

O

H

O=

H-

H-

-H

-CH2-CH2-S-CH3

Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


mthionine (M)



+

ACIDE AMINE A CHAINE ALIPHATIQUE ET A FONCTION SOUFRE.


H

N

C

C

O

H

O=

H-

H-

-H

-CH2-C-NH2

Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


asparagine (N)


O


+

ACIDE AMINE A CHAINE ALIPHATIQUE ET A FONCTION ACIDE.


H

N

C

C

O

H

O=

H-

H-

-H

-CH2-C-OH

Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


aspartate (D)

O


+



H

N

C

C

O

H

O=

H-

H-

-H

-CH2-CH2-C-NH2

Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


glutamine (Q)

O


+


Acides amins carbone oxygne hydrogne azote soufreAcides amins carbone oxygne hydrogne azote soufre

H

N

C

C

O

H

O=

H-

H-

-H

-CH2-CH2-C-OH

Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


glutamate (E)

O


+



H

N

C

C

O

H

O=

H-

H-

-H

-(CH2)4-NH3

Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


lysine (K)



+

+

ACIDE AMINE A CHAINE ALIPHATIQUE A FONCTION BASIQUE.


H

N

C

C

O

H

O=

H-

H-

-H

-(CH2)3-NH-C-NH2

Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


arginine (R)


NH2

+

+



H

N

C

C

O

H

O=

H-

H-

-H

-CH2-

Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


histidine (H)


N-H

NH

HHacide amin essentiel

+


+


H

N

C

C

O

H

O=

H-

H-

-H

-CH2-

Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


phnylalanine (F)



+

ACIDE AMINE A CHAINE CYCLIQUE ET AROMATIQUE.


H

N

C

C

O

H

O=

H-

H-

-H

-CH2- -OH

Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


tyrosine (Y)


+




Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


tryptophane (W)



H

N

C

C

O

H

O=

H-

H-

-H

-CH2-

NHH

+


H

N

C

C

O

H

O=

H-

H- -CH2

Chane latrale R



PHE TYR TRP LYS

ARG HIS ASP GLU


proline (P)

CH2

CH2


+

ACIDE AMINE HETEROCYCLIQUE

Classification des acides amins selon la polarit de la chane latrale

Acides amins non polaires ou hydrophobes

Gly, Ala, Val, Leu, Ile, Met, Phe, Trp, Pro

Acides amins neutres (non chargs) mais polaires

Ser, Thr, Cys, Asn, Gln, Tyr

Acides amins acides (chargs (-) pH > 3)

Asp, Glu

Acides amins basiques (chargs (+) pH physiol.)

Lys, Arg, His

Classification des acides amins selon leur importance alimentaire:

Les acides amins essentiels:

valine, leucine, isoleucine, phnylalanine, tryptophane, methionine, thronine, histidine (essentielle pour les nourrissons), lysine, arginine (semi-essentielle).

Les acides amins non-essentiels:

glycine, alanine, proline, serine, cystine, tyrosine, asparagine, glutamine, acide asparagique, acide glutamique.

NomCode

1 lettre

Code

3 lettres

Masse

molaire

(g.mol-1)

pIpK1(-

COOH)pK2 (-NH2) pKR (-R)

Abondan

ce

relative

dans

Swiss-

Prot (%)

Alanine A Ala 89.09 6.01 2.35 9.87 7.86

Arginine R Arg 174.20 10.76 1.82 8.99 12.48 5.39

Asparagi

neN Asn 132.12 5.41 2.14 8.72 4.15

Aspartate D Asp 133.10 2.85 1.99 9.90 3.90 5.34

Cystine C Cys 121.16 5.05 1.92 10.70 8.18 1.51

Glutamat

eE Glu 147.13 3.15 2.10 9.47 4.07 6.66

Glutamin

eQ Gln 146.15 5.65 2.17 9.13 3.95

Glycine G Gly 75.07 6.06 2.35 9.78 6.94

Histidine H His 155.16 7.60 1.80 9.33 6.04 2.29

Isoleucin

eI Ile 131.17 6.05 2.32 9.76 5.91

Leucine L Leu 131.17 6.01 2.33 9.74 9.64

Lysine K Lys 146.19 9.60 2.16 9.06 10.54 5.93

Mthionin

eM Met 149.21 5.74 2.13 9.28 2.37

Phnylala

nineF Phe 165.19 5.49 2.20 9.31 3.97

Proline P Pro 115.13 6.30 1.95 10.64 4.81

Documents

acides aminés 1