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Structure of Amino Acids
Amino Acids
• Amino acids are the structural building blocks
(monomers) of proteins.
• There are twenty different kinds of amino
acids used in proteins.
• Proteins are referred to as heteropolymers
due the variety of amino acids involved in
their structure.
a-carbon
Amino Acids (cont’d.)
• Amino acids, like carbohydrates, show
isomerism. Proteins are only made up of
amino acids which are L-isomers.
L-isomer
D-isomer
Amino Acids (cont’d.)
• At neutral pH’s amino acids exist in an ionised
form and have both acidic and basic
properties. This is because the carboxylic
group donates hydrogen ions to the solution
(acidic) whereas the amino group (NH2)
attracts hydrogen ions from the solution.
Amino Acids (cont’d.)
• The repeating sequence of atoms along a
proteins is referred to as the polypeptide
backbone. Attached to this repetitive chain
are the different amino acid side chains
(R-groups) which are not involved in the
peptide bond but which give each amino acid
its unique property.
Amino Acids (cont’d.)
• Amino acids are grouped according to
whether their side chains are:• acidic
• basic
• uncharged polar
• non polar
Aspartic
Acid
Glutamic
Acid
asp
glu
A
s
p
a
r
a
t
s
i D
p
c
A
c
i
d
A
c
i
d
i
c
P
o
l
a
r
Acidic
Polar
Acidic
Polar
Lysine
lys
Basic
Polar
Arginine
arg
Basic
Polar
Glutamine
Tyrosine
gln
tyr
Neutral
Polar
Neutral
Polar
Isoleucine
ile
Neutral
Non-polar
Methionine
met
Neutral
Non-polar
Amino Acids (cont’d.)
• The type of side chain is very important as it
affects the solubility of the amino acid.
• Hydrophobic features include long nonpolar (uncharged) chains or complex aromatic
rings.
• Hydrophilic features include additional
carboxyl groups or amino groups not involved
in peptide bonding which are ionised in
solution.
Amino Acids (cont’d.)
• Amino acids link together by covalent peptide
bonds. This involves a condensation
/dehydration reaction. These bonds are
very strong. When this takes place the
charged amino and carboxylic groups
disappear.