Amono Acids Reference Sheet
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28. Amino Acids
The simplest amino acid is
NH
CH
CO
H
General structure of an amino acid
2
2
2
glycine, where the R is an H
NH
CH
CO
H
2
2
Optical Activity
R
H
H
All amino acids, except
The R group can be a variety of
glycine, are chiral because
C
C
different things depending on what
there are four different groups
H
N
CO
H
HO
C
2
amino acid it is.
2
around the C
2
NH
2
CH
CH
3
3
They rotate plane polarised light.
Naming amino acids
CO
H
Some amino acids have an extra
2
CO
H
2
You do not need to know any
carboxylic acid or an amine
CH
CH
2
common names for the 20
2
group on the R group. These are
NH
C
CO
H
NH
C
CO
H
2
2
essential amino acids. We
classed as acidic or basic
2
2
H
should, however, be able to
H
(respectively) amino acids
2-aminobutanedioic acid
name given amino acids using
Aspartic acid
OH
IUPAC organic naming
CO
H
2
CH
2
H
C
(CH
)
NH
2
4
2
NH
CH
CO
H
NH
C
CO
H
Lycine (basic)
2
2
2
2
2
H
N
2
2,6-diaminohexanoic acid
H
2-amino-3-
(2-)aminoethanoic acid
hydroxypropanoic acid
Zwitterions
R
R
The no charge form of an amino acid never occurs.
+
-
H
N
C
CO
H
H
N
C
CO
The amino acid exists as a dipolar zwitterion.
2
2
3
2
H
H
Amino acids are often solids
Zwitterion
The ionic interaction between zwitterions explains the relatively high melting points of amino acids as
opposed to the weaker hydrogen bonding that would occur in the no charge form.
Acidity and Basicity
Amino acids act as weak buffers and will
The amine group is basic and the carboxylic acid group is acidic.
only gradually change pH if small
-
+
OH
H
R
R
R
amounts of acid or alkali are added to the
-
+
-
+
amino acids.
H
N
C
CO
H
N
C
CO
H
N
C
CO
H
2
2
3
2
3
2
NH
-CH
-CO
+ HCl
Cl
NH
-CH
-CO
H
+
-
-
+
H
H
H
3
2
2
3
2
2
+
-
H
OH
NH
-CH
-CO
+ NaOH
NH
-CH
-CO
Na
+H
O
+
-
-
+
Species in
Species in
Species in
3
2
2
2
2
2
2
alkaline solution
neutral solution
acidic solution
High pH
Low pH
Proteins
CH
3
CH
H
C
S
Proteins are polymers made from
3
3
CH
combinations of amino acids.
H
S
CH
2
The amino acids are linked by peptide links,
CH
CH
CH
CH
O
O
O
O
3
2
2
2
which are the amide functional group.
H
N
CH C
N CH C
N CH C
N CH C
O
H
O
O
O
H
H
H
H
NH
CH
C
NH
CH
C
NH
CH
C
R
R
R
N Goalby
1
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