© www.chemsheets.co.uk A2 022 15-Jul-12 AMINO ACIDS H H 2N amine group C CO O H carboxylic acid group R © www.chemsheets.co.uk A2 022 15-Jul-12

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Transcript © www.chemsheets.co.uk A2 022 15-Jul-12 AMINO ACIDS H H 2N amine group C CO O H carboxylic acid group R © www.chemsheets.co.uk A2 022 15-Jul-12

AMINO ACIDS amine group

H 2 N H C R COOH

carboxylic acid group

H 2 N H C H COOH

glycine

H 2 N H C CH 3 COOH

alanine

H 2 N H C CH COOH CH 3 CH 3

valine

H 2 N H C COOH CH 2 OH

serine

H 2 N H C COOH CH 2 COOH

aspartic acid

From nobelprize.org

• amino acids are chiral (except glycine where R = H) • only one enantiomer occurs usually Public domain image from wikipedia

Low pH (acidic)

H H 3 N

C R COOH

Neutral pH

H 2 N H C R COOH

High pH (alkaline)

H 2 N H C R COO

H H 3 N

C COO

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

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

pH 12 H 2 N H C CH 3 COOH pH 4 H 2 N H C COOH CH 2 OH pH 2 pH 13 H 2 N H C H COOH H 2 N H C COOH CH 2 COOH © www.chemsheets.co.uk A2 022 15-Jul-12

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

pH 12 H 2 N H C CH 3 COO

pH 4 H H 3 N

C COOH CH 2 OH pH 2 H 3 N

H C pH 13 H COOH H 2 N H C COO CH 2 COO

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Joining amino acids together to make polypeptides and proteins: H H H 2 N C COOH + H 2 N C COOH R R - H 2 O Condensation reaction: molecules join and water is eliminated H O H H 2 N C R C N H C R COOH © www.chemsheets.co.uk A2 022 15-Jul-12

Breaking down polypeptides and proteins into amino acids: H 2 N H C R O C N H H C R COOH Needs: acid or enzyme + H 2 O Hydrolysis reaction: reaction with water in which O-H bond breaks H 2 N H C R COOH + H H 2 N C COOH R © www.chemsheets.co.uk A2 022 15-Jul-12

Public domain image from wikipedia

Public domain image from wikipedia Helix held in shape by hydrogen bonds