© A2 022 15-Jul-12. AMINO ACIDS amine group carboxylic acid group © A2 022 15-Jul-12

© www.chemsheets.co.uk A2 022 15-Jul-12

H2N C

H

R

COOH

AMINO ACIDS

amine group

carboxylic acid

group


glycine

H

C COOHH2N

H


alanine

H

C COOHH2N

CH3


valine

H

C COOHH2N

CH

CH3

CH3


serine

H

C COOHH2N

CH2OH


aspartic acid

H

C COOHH2N

CH2COOH


From nobelprize.org

• amino acids are chiral (except glycine where R = H)

• only one enantiomer occurs usually

Public domain image from wikipedia

H

C COOH2N

R

_H

C COOHH2N

R

_+

H

C COOH3N

R

zwitterion

H

C COOHH3N

R

+

Neutral pH High pH (alkaline)

Low pH (acidic)


Draw the structure of the amino acid at the pH shown.

H

C COOHH2N

CH3

H

C COOHH2N

CH2OH

H

C COOHH2N

H

pH 12

pH 4

pH 2

pH 13 H

C COOHH2N

CH2COOH


Draw the structure of the amino acid at the pH shown.

pH 12

pH 4

pH 2

pH 13

H

C COOH2N

CH3

_

H

C COOHH3N

CH2OH

+

H

C COOHH3N

H

+

H

C COOH2N

CH2COO

_

_


Joining amino acids together to make polypeptides and proteins:

H2N C

H

R

COOH H2N C

H

R

COOH+

- H2O

H2N C

H

R

C

O

N

H

C

H

COOH

R

Condensation reaction: molecules join and water is eliminated


Breaking down polypeptides and proteins into amino acids:

Hydrolysis reaction: reaction with water in which O-H bond breaks

H2N C

H

R

COOH H2N C

H

R

COOH+

+ H2O

H2N C

H

R

C

O

N

H

C

H

COOH

R

Needs: acid or enzyme





Helix held in shape by

hydrogen bonds



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© A2 022 15-Jul-12. AMINO ACIDS amine group carboxylic acid group © A2 022 15-Jul-12