© a2 022 15-jul-12. amino acids amine group carboxylic acid group © a2 022 15-jul-12
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H2N C
H
R
COOH
AMINO ACIDS
amine group
carboxylic acid
group
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glycine
H
C COOHH2N
H
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alanine
H
C COOHH2N
CH3
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valine
H
C COOHH2N
CH
CH3
CH3
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serine
H
C COOHH2N
CH2OH
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aspartic acid
H
C COOHH2N
CH2COOH
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From nobelprize.org
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• amino acids are chiral (except glycine where R = H)
• only one enantiomer occurs usually
Public domain image from wikipedia
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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)
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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
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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
_
_
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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
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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
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Public domain image from wikipedia
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Helix held in shape by
hydrogen bonds
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