Overview of Amino Acid

Overview of Amino Acid

Overview of Amino Acid

This entry is from Wikipedia, the leading user-contributed encyclopedia.

In chemistry, an amino acid is a molecule that contains both amine and carboxyl functional groups. In biochemistry, this term refers to alpha-amino acids with the general formula NH2CHRCOOH.[1] These are molecules where the amino and carboxylate groups are attached to the same carbon, which is called the α–carbon. The various alpha amino acids differ in which side chain (R group) is attached to their alpha carbon. This can vary in size from just a hydrogen atom in glycine, through a methyl group in alanine, to a large heterocyclic group in tryptophan.

Alpha-amino acids are the building blocks of proteins. Proteins form via the condensation of amino acids to form a chain of amino acid "residues" linked by peptide bonds. Each different protein has a unique sequence of amino acid residues; this sequence is the primary structure of the protein. Just as the letters of the alphabet can be combined to form an almost endless variety of words, amino acids can be linked in varying sequences to form a huge variety of proteins.

There are twenty standard amino acids used by cells in protein biosynthesis, and these are specified by the general genetic code. These twenty amino acids are biosynthesized from other molecules, but organisms differ in which ones they can synthesize and which ones must be provided in their diet. The ones that cannot be synthesized by an organism are called essential amino acids.

Table of standard amino acid abbreviations and side chain properties

Amino Acid  

3-Letter  

1-Letter  

Side chain polarity  

Side chain acidity 
  or basicity  

Hydropathy index[17]  

Alanine

Ala

A

nonpolar

neutral

1.8

Arginine

Arg

R

polar

strongly basic

-4.5

Asparagine

Asn

N

polar

neutral

-3.5

Aspartic acid

Asp

D

polar

acidic

-3.5

Cysteine

Cys

C

polar

neutral

2.5

Glutamic acid

Glu

E

polar

acidic

-3.5

Glutamine

Gln

Q

polar

neutral

-3.5

Glycine

Gly

G

nonpolar

neutral

-0.4

Histidine

His

H

polar

weakly basic

-3.2

Isoleucine

Ile

I

nonpolar

neutral

4.5

Leucine

Leu

L

nonpolar

neutral

3.8

Lysine

Lys

K

polar

basic

-3.9

Methionine

Met

M

nonpolar

neutral

1.9

Phenylalanine

Phe

F

nonpolar

neutral

2.8

Proline

Pro

P

nonpolar

neutral


Serine

Ser

S

polar

neutral

-0.8

Threonine

Thr

T

polar

neutral

-0.7

Tryptophan

Trp

W

nonpolar

neutral

-0.9

Tyrosine

Tyr

Y

polar

neutral

-1.3

Valine

Val

V

nonpolar

neutral

4.2