This document discusses the structure and classification of amino acids. It begins by stating that amino acids are the basic structural units of proteins and that there are 20 standard amino acids found in protein structures. The general structure of an amino acid is presented, showing that they contain an amino group, a carboxyl group, and a variable R group (side chain) attached to the alpha carbon. Amino acids are then classified into four types based on the polarity of their R groups: non-polar aliphatic, non-polar aromatic, polar uncharged, and polar charged (acidic or basic). Examples of amino acids that fall into each of these four categories are provided.
2. • Amino acids are the basic structural units of proteins.
• 20 different amino acids are found in the structure of proteins.
• These amino acids present in protein are called standard or
protein amino acids.
• There are many other amino acids found free in nature. They
are referred to as non-protein amino acids. Eg. Ornithine,
citrulline.
INTRODUCTION
3. GENERAL STRUCTURE
C
R
COOH
H
NH2
General formula of
Amino acids
All protein amino acids have an amino group, and a carboxyl
group attached to the - carbon atom.
The R-group is referred to as the side chain of amino acids.
Amino acids differ by the R-group
COOH
NH2
C
CH3
H
COOH
NH2
C
H
H
Alanine Glycine
4. CLASSIFICATION
Amino acids are classified into four types based on the polarity of
the R groups.
Amino acids with non-polar (hydrophobic), aliphatic
R groups
Amino acids with non-polar aromatic R groups
Amino acids with polar uncharged R groups
Amino acids with polar charged R groups – Acidic or
Basic
5. I. Non-polar or hydrophobic aliphatic side chain
1. Glycine Gly G
2. Alanine
Ala A
3. Valine
Val V
4. Leucine Leu L
5. Isoleucine
Ile I
COOH
NH2
CH
H
COOH
NH2
CH
H3C
COOH
NH2
CH
H3C
H3C
CH
COOH
NH2
CH
H3C
H3C
CH CH2
COOH
NH2
CH
H3C
CH3
CH2 CH
6. Proline Pro P
H2C
COOH
NH
CH2
H2C
CH
6. II. Non-polar aromatic side chain
7. Phenyl alanine Phe F
8. Tyrosine Tyr Y
9. Tryptophan
(Indole ring)
Trp W
COOH
NH2
CH
CH2
COOH
NH2
CH
CH2
OH
CH COOH
NH2
CH2
N
H
7. III. Polar neutral side chain
10. Serine Ser S
11. Threonine Thr T
COOH
NH2
CH
HO CH2
OH
COOH
NH2
CH
H3C CH
12. Cysteine Cys C
13. Methionine Met M
COOH
NH2
CH
HS CH2
H3C COOH
NH2
CH
S CH2
CH2
14. Asparagine
15. Glutamine
Asn N
Gln Q
O
COOH
NH2
CH
CH2
C
H2N
COOH
NH2
CH
CH2
CH2
O
C
H2N
(Amide group)
(Hydroxyl group)
(Sulphur containing)
8. 16. Aspartic acid
Asp D
17. Glutamic acid
Glu E
IV. Polar Acidic side chain (Negatively charged)
COOH
NH2
CH
CH2
HOOC
HOOC COOH
NH2
CH
CH2
CH2
Polar Basic side chain (Positively charged)
18. Lysine
Lys K
19. Arginine
Arg R
20. Histidine
His H
COOH
NH2
CH
CH2
CH2
CH2
CH2
H2N
C COOH
NH2
CH
CH2
CH2
CH2
NH
H2N NH
CH COOH
NH2
CH2
N
HN
(Guanidine group)
(Imidazole group)
