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© www.chemsheets.co.uk A2 022 15-Jul-12
H2N C
H
R
COOH
AMINO ACIDS
amine group
carboxylic acid
group
© www.chemsheets.co.uk A2 022 15-Jul-12
glycine
H
C COOHH2N
H
© www.chemsheets.co.uk A2 022 15-Jul-12
alanine
H
C COOHH2N
CH3
© www.chemsheets.co.uk A2 022 15-Jul-12
valine
H
C COOHH2N
CH
CH3
CH3
© www.chemsheets.co.uk A2 022 15-Jul-12
serine
H
C COOHH2N
CH2OH
© www.chemsheets.co.uk A2 022 15-Jul-12
aspartic acid
H
C COOHH2N
CH2COOH
© www.chemsheets.co.uk A2 022 15-Jul-12
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)
© www.chemsheets.co.uk A2 022 15-Jul-12
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
© www.chemsheets.co.uk A2 022 15-Jul-12
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
_
_
© www.chemsheets.co.uk A2 022 15-Jul-12
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
© www.chemsheets.co.uk A2 022 15-Jul-12
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
© www.chemsheets.co.uk A2 022 15-Jul-12
Public domain image from wikipedia
Public domain image from wikipedia
Public domain image from wikipedia
Helix held in shape by
hydrogen bonds
Public domain image from wikipedia
Public domain image from wikipedia
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