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Proteins are built
from 20 kinds of
alpha-amino acids.
21st aa = selenocysteine
“CO-R-N” clockwise
When viewing down
from H to C-alpha
 L-amino acid
Free -SH group
of cysteine:
S
S
-Reacts readily
with heavy metals
-Easily oxidized
pKa
Three- and one-letter codes for
amino acids
Disulfide bond
Insulin sequence
Modified amino
cid residues
Rotation around
this C-N bond is
not free.
Peptide unit:
-Rigid
-Usually trans
-Dipole moment
H
These two bonds are
free to rotate.
0.5+
0.5Alpha-helix has a large dipole moment.
Antiparallel
beta-sheet
Proteins:
-Fibrous proteins
eg. keratin, collagen, sil
Collagen sequence
-Globular proteins
Collagen triple helix
G, Gly
Myoglobin is rich
in alpha-helices.
Ribonuclease: beta
and alpha
4 disulfide bonds
Hemoglobin: tetramer
Beta-alpha-beta motif:
The crossover connection
is nearly always righthanded.
Poliovirus: 60-mer
Antibody light chain:
beta-sandwich
Ribonuclease
sequence
Refolding of proteins is
very difficult.
Proteins can
be easily
denatured.
Conformational change is
important for function.