Protein & amino acid
Proteins play key roles in a living
system
• Three examples of protein functions
– Catalysis:
Almost all chemical reactions in a living
cell are catalyzed by protein enzymes.
Alcohol
dehydrogenase
oxidizes alcohols
to aldehydes or
ketones
– Transport:
Some proteins transports various
substances, such as oxygen, ions, and so Haemoglobin
carries oxygen
on.
– Information transfer:
For example, hormones.
Insulin controls
the amount of
sugar in the
blood
Amino acid: Basic unit of protein
R
NH3
+
C
Amino group
H
Different side chains,
R, determin the
COO properties of 20
Carboxylic
acid group
amino acids.
An amino acid
20 Amino acids
Glycine (G)
Alanine (A)
Valine (V)
Isoleucine (I)
Leucine (L)
Proline (P)
Methionine (M)
Phenylalanine (F)
Tryptophan (W)
Asparagine (N)
Glutamine (Q)
Serine (S)
Threonine (T)
Tyrosine (Y)
Cysteine (C)
Lysine (K)
Arginine (R)
Histidine (H)
Asparatic acid (D) Glutamic acid (E)
White: Hydrophobic, Green: Hydrophilic, Red: Acidic, Blue: Basic
Proteins are linear polymers of amino
acids
R1
NH3＋
C
R2
COOー
＋
NH3＋
H
H
H2O
A
R2
R3
C
CO
NH
C
CO
NH
C
H
Peptide
bond
H
Peptide
bond
H
F
G
N
S
T
D
K
G
S
A
＋
A carboxylic acid
condenses with an amino
group with the release of a
water
H2O
R1
NH3＋
COOー
C
CO
The amino acid
sequence is called as
primary structure
Peptide bond
• Joins amino acids
• 40% double bond character
– Caused by resonance
– Results in shorter bond length
– Double bond disallows rotation
Amino acid sequence is encoded by
DNA base sequence in a gene
DNA
molecule
＝
・
G
C
G
C
T
T
A
A
G
C
G
C
・
・ DNA base
C
G sequence
C
G
A
A
T
T
C
G
C
G
・
Amino acid sequence is encoded by
DNA base sequence in a gene
T
T
A
G
Phe
Leu
Leu
Ile
Met
Val
TCT
TCC
TCA
TCG
CCT
CCC
CCA
CCG
ACT
ACC
ACA
ACG
GCT
GCC
GCA
GCG
Ser
Pro
Thr
Ala
TAT
TAC
TAA
TAG
CAT
CAC
CAA
CAG
AAT
AAC
AAA
AAG
GAT
GAC
GAA
GAG
G
Tyr
Stop
His
Gln
Asn
Lys
Asp
Glu
TGT
TGC
TGA
TGG
CGT
CGC
CGA
CGG
AGT
AGC
AGA
AGG
GGT
GGC
GGA
GGG
Cys
Stop
Trp
Arg
Ser
Arg
Gly
T
C
A
G
T
C
A
G
T
C
A
G
T
C
A
G
Third letter
First letter
C
TTT
TTC
TTA
TTG
CTT
CTC
CTA
CTG
ATT
ATC
ATA
ATG
GTT
GTC
GTA
GTG
C
Second letter
A