Biomedical Engineering Reference
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COO -
COO -
COO -
COO -
COO -
COO -
+
+
+
+
+
+
H 3 N C
H
H 3 N C
H
H 3 N C
H
H 3 N C
H
H 3 N C
H
H 3 N C
H
CH 3
H
CH
CH 2
CH 2
CH 2
CH 3
CH 3
C
CH
Alanine
Valine
Glycine
NH
COO -
COO -
COO -
H
OH
C
+
+
+
H 3 N C
H
H 3 N C
H
H 2 N
CH 2
Phenylalanine
Tyrosine
Tryptophan
CH 2
H
C
CH 3
H 2 C
CH 2
CH
CH 2
COO -
COO -
COO -
+
CH 3
CH 3
+
+
CH 3
H 3 N C
H
H 3 N C
H
H 3 N C
H
Leucine
Isoleucine
Proline
CH 2
CH 2
CH 2
CH 2
CH 2
COO -
COO -
COO -
C
NH
+
+
+
CH 2
CH 2
CH
H 3 N C
H
H 3 N C
H
H 3 N C
H
+
C
H
N
H
CH 2
NH
H
C
OH
CH 2 OH
CH 2
+
+ NH 3
NH 2
C
CH 3
SH
NH 2
Serine
Threonine
Cysteine
Lysine
Arginine
Histidine
COO -
COO -
COO -
+
+
+
COO -
COO -
H 3 N C
H
H 3 N C
H
H 3 N C
H
+
+
CH 2
CH 2
CH 2
H 3 N C
H
H 3 N C
H
CH 2
C
CH 2
CH 2
CH 2
H 2 N
O
S
COO -
C
CH 2
H 2 N
O
CH 3
COO -
Methionine
Asparagine
Glutamine
Aspartate
Glutamate
Figure 2.1 The chemical structure of the 20 amino acids commonly found in proteins
As will be evident from Section 2.2.2, peptide bond formation between adjacent amino acid resi-
dues entails the establishment of covalent linkages between the amino and carboxyl groups attached
to their respective central (
) carbon atoms. Hence, the free functional (i.e. chemically reactive)
groups in polypeptides are almost entirely present as part of the constituent amino acids' side chains
(R groups). In addition to determining the chemical reactivity of a polypeptide, these R groups
also very largely dictate the fi nal conformation adopted by a polypeptide. Stabilizing/repulsive
forces between different R groups (as well as between R groups and the surrounding aqueous me-
dia) largely dictate what fi nal shape the polypeptide adopts, as will be described later.
α
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