Amino Acids

Amino Acids (Chapter 37B)

General Structures 

Two contrasting groups  

 

-COOH acidic -NH3 basic

α-amino acids ~20 different αamino acids found in protein in nature

COOH α

H 2N C H R

Some amino acids COOH H 2N C H H

COOH H 2N C H CH2COOH

COOH H 2N C H CH3

Aminoethanoic 2-Aminopropanoic Aminobutanoic acid acid acid (Aspartic acid) (Glycine) (Alanine)

Chirality  

L-amino acid Look down at H-C bond, other groups, read clockwise (‘corn’ law)

COO-

C

R

H3N+ H

eye

Special features 

High m.p. and b.p. 

  

Glycine (R=H) is a solid

Soluble in water High dipole moment Less acidic and basic than normal RCOOH and RNH2

COO+

H 3N C H R Dipolar Ion (Switterion)

Amphoteric COOCOO- As acid H3N

+

H2N C H + H3O+

C H R

+ H2O

R As base

COOH +

H3N

C H R

+ OH-

Isoelectric point COO-

COOOH-

H2N

C

H

H+

H3N C

+

H+

R (II)

COOH

R (I)

H

+

OH-

H3N C R (III)

pH at which the concentrations of (II) = (III) is called the isoelectric point.

H

Separating amino acids 

Chromatography

Separating amino acids 

Electrophoresis

Peptide Linkage H H3N+ C R

H

O C

H N+ C

O-

H -H2O

H O H3N+ C R

H

C

H

R’

C

R’

H

N C

O

O C

O-

O-

Peptide linkage (A Dipeptide)

Proteins  



Polypeptides About 20 amino acids Number of possible protein polymers is very large

H O HN C R

C

H

H O

N C R’

C n

Proteins