Amono Acids Reference Sheet Page 2
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1
2Dipeptides
Dipeptides are simple combination molecules of
For any two different amino acids there are two possible
two amino acids with one amide (peptide) link.
combinations of the amino acids in the dipeptide.
H
O
H
O
H
O
CH
3
H
H
CH
CH
Can make
CH
CH
2
2
CH
3
3
or
2
H
N
C
CO
H
+
2
2
H
N
C
C
H
N
C
C
N
C
CO
H
N
C CO
H
2
2
2
2
H
N
C
CO
H
H
2
2
H
H
O
H
H
O
H
O
O
Importance of hydrogen bonding in proteins
δ-
δ-
N
CH
C
N
CH
C
The 3D arrangement of amino acids with the
δ+
polypeptide chain in a corkscrew shape is held in
δ+
H
H
R
R
δ-
place by Hydrogen bonds between the H of –N
—
δ+
δ+
δ-
H
group and the –O of C
=O
δ-
O
O
δ-
N
CH
C
N
CH
C
δ+
H
H
R
R
Hydrolysis of di-peptides/proteins
If proteins are heated with dilute acid or alkali they can be
The composition of the protein
hydrolysed and split back in to their constituent amino acids.
molecule may then be deduced by
using paper chromatography
CH
H
C
3
3
CH
CH
H
C
3
3
CH
CH
CH
O
O
CH
3
2
O
+
H
3
+
CH
O
H
N
CH C
N CH C
O
H
2
H
N
CH C
O
H
+
3
+
H
N
CH C
O
H
3
H
H
Chromatography of Amino Acids
Method
A mixture of amino acids can be separated by
Take chromatography paper and
chromatography and identified from the amount
draw a pencil line 1.5cm from
they have moved.
bottom.
With a capillary tube put a small
drop of amino acid on pencil line
R
value = distance moved by amino acid
f
Roll up paper and stand it in a large
distance moved by the solvent
beaker.
The solvent in the beaker should be
below the pencil line.
Each amino acid has its own R
value
f
Allow to stand for 20 mins and mark
final solvent level
Spray paper with ninhydrin and put
in oven
Other reactions of amino acids
The carboxylic acid group and amine group in amino acids can undergo the usual reactions of these functional groups met
in earlier topics. Sometimes questions refer to these.
e.g. Esterification reaction
CH
O
3
CH
3
+
+
H
O CH
H
N
C
C
+ H
O
H
N
C
CO
H
3
3
2
+ CH
OH
2
2
3
H
H
N Goalby
2
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