Chon structures 2

CHONS WK 2 BIOCHEM LEC

1. PROTEIN STRUCTURES PROTEIN STRUCTURES
&&
FUNCTIONSFUNCTIONS

2. FUNCTIONS
Proteins function as:
1. Enzymes:biological catalysts
2. Regulators of catalysis-hormones
3. Transport and store i.e. O2, metal
ions sugars, lipids, etc.

3. FUNCTIONS
4. Contractile assemblies
Muscle fibers
5. Sensory
Rhodopsin nerve proteins
6. Cellular defense (antibodies/Ig)
7. Structural (collagen)

4. Proteins play key roles in a Proteins play key roles in a
living systemliving system
examples of protein functions
Catalysis:
Almost all chemical reactions in a
living cell are catalyzed by protein
enzymes.
Transport:
Some proteins transports various
substances, such as oxygen, ions,
and so on.
Information transfer:
For example, hormones.
Alcohol
dehydrogenase
oxidizes alcohols
to aldehydes or
ketones
Hemoglobin
carries oxygen
Insulin controls
the amount of
sugar in the
blood

5. Amino acid: Basic unit of Amino acid: Basic unit of
proteinprotein
COO
-
NH
3
+
C
R
H
An amino acid
Different side chains,
R, determin the
properties of 20
amino acids.
Amino group Carboxylic
acid group

6. 20 Amino acids20 Amino acids
Glycine (G)
Glutamic acid (E)Asparatic acid (D)
Methionine (M)
Threonine (T)Serine (S)Glutamine (Q)
Asparagine (N)Tryptophan (W)Phenylalanine (F)
Cysteine (C)
Proline (P)
Leucine (L)Isoleucine (I)Valine (V)Alanine (A)
Histidine (H)Lysine (K)
Tyrosine (Y)
Arginine (R)
White: Hydrophobic, Green: Hydrophilic, Red: Acidic, Blue: Basic

7. Proteins are linear polymers of Proteins are linear polymers of
amino acidsamino acids
R
1
NH
3
＋
CCO
H
R
2
NHCCO
H
R
3
NHCCO
H
R
2
NH
3
＋
CCOO
ー
H
＋
R
1
NH
3
＋
CCOO
ー
H
＋
H
2
OH
2
O
Peptide
bond
Peptide
bond
The amino acid
sequence is called as
primary structure
A A
F
N
G
G
S
T
S
D
K
A carboxylic acid
condenses with an amino
group with the release of a
water

8. Amino acid sequence is encoded Amino acid sequence is encoded
by DNA base sequence in a geneby DNA base sequence in a gene
・
C
G
C
G
A
A
T
T
C
G
C
G
・
・
G
C
G
C
T
T
A
A
G
C
G
C
・
DNA
molecule
＝
DNA base
sequence

9. Amino acid sequence is encoded Amino acid sequence is encoded
by DNA base sequence in a geneby DNA base sequence in a gene
Second letter
T C A G
F
i
r
s
t

l
e
t
t
e
r
T
TTT
Phe
TCT
Ser
TAT
Tyr
TGT
Cys
T
T
h
i
r
d

l
e
t
t
e
r
TTC TCC TAC TGC C
TTA
Leu
TCA TAA
Stop
TGA Stop A
TTG TCG TAG TGG Trp G
C
CTT
Leu
CCT
Pro
CAT
His
CGT
Arg
T
CTC CCC CAC CGC C
CTA CCA CAA
Gln
CGA A
CTG CCG CAG CGG G
A
ATT
Ile
ACT
Thr
AAT
Asn
AGT
Ser
T
ATC ACC AAC AGC C
ATA ACA AAA
Lys
AGA
Arg
A
ATG Met ACG AAG AGG G
G
GTT
Val
GCT
Ala
GAT
Asp
GGT
Gly
T
GTC GCC GAC GGC C
GTA GCA GAA
Glu
GGA A
GTG GCG GAG GGG G

10. Basic structural units of proteins: Basic structural units of proteins:
Secondary structureSecondary structure
α-helix
β-sheet
Secondary structures, α-helix
and β-sheet, have regular
hydrogen-bonding patterns.

11. Three-dimensional structure Three-dimensional structure
of proteinsof proteins
Tertiary
structure
Quaternary structure

12. Hierarchical nature of protein Hierarchical nature of protein
structurestructure
Primary structure (Amino acid sequence)
↓
Secondary structure （α-helix, β-sheet）
↓
Tertiary structure （Three-dimensional structure
formed by assembly of secondary structures）
↓
Quaternary structure （Structure formed by more
than one polypeptide chains）