Amino acid : Formula, Structure, Functions

Published on 13-Aug-2025

Amino Acids

Amino acids are organic molecules that act as building blocks of proteins. Nobel Prize-winning scientists Emil Fischer and Franz Hofmeister discovered amino acids as the building blocks of protein molecules in 1902.

An organic acid formed by replacing one or more hydrogen atoms of an organic acid with an amino group (-NH2) is called an amino acid. Each amino acid contains at least one amino group (-NH2) and one carboxyl group (-COOH). It may also have other active functional groups. The properties of an amino acid depend on its functional group.

There are different types of amino acids in plants. Twenty amino acids are combined and arranged in various ways to form other proteins.

General Structure of Amino Acids

The carbon atom near the carboxyl group of an amino acid is called the α-carbon, and when the carboxyl group is attached to the α-carbon, it is called the α-amino acid.

Chemical structure of amino acids:

The common chemical formula of amino acids is:

R-CH(NH2)-COOH

R is a hydrogen atom or an organic compound containing carbon.
Amino acids contain at least one amino group (-NH2), one carboxyl group (-COOH), and a side chain group (R).

Some amino acids may contain 2 amino groups, 2 carboxyl groups, or sulfur. For example:

Glycine: R group is H.
Serine: R group is CH2OH.
Cysteine: R group is CH2SH.

Properties of Amino Acids

Soluble in water but insoluble in alcohol.
Tasteless, sweet, or bitter substances.
Colorless, crystalline substances.
Form salts with mild acids or bases.
Can be obtained by complete hydrolysis (wet-analysis) of proteins.
Joined together by peptide bonds to form proteins.
Acidic and basic amino acid groups are called zwitterions.

Amino Acid List

Serial	Amino Acid	Chemical Formula	Molecular Weight	3-letter Abbreviation	1-letter Abbreviation
1	Alanine	C3H7NO2	89.09 g/mol	Ala	A
2	Arginine	C6H14N4O2	174.2 g/mol	Arg	R
3	Asparagine	C4H8N2O3	132.12 g/mol	Asn	N
4	Aspartic acid	C4H7NO4	133.11 g/mol	Asp	D
5	Cysteine	C3H7NO2S	121.16 g/mol	Cys	C
6	Glutamic acid	C5H9NO4	147.13 g/mol	Glu	E
7	Glutamine	C5H10N2O3	146.14 g/mol	Gln	Q
8	Glycine	C2H5NO2	75.07 g/mol	Gly	G
9	Histidine	C6H9N3O2	155.157 g/mol	His	H
10	Isoleucine	C6H13NO2	131.17 g/mol	Ile	I
11	Leucine	C6H13NO2	131.17 g/mol	Leu	L
12	Lysine	C6H14N2O2	146.19 g/mol	Lys	K
13	Methionine	C5H11NO2S	149.21 g/mol	Met	M
14	Phenylalanine	C9H11NO2	165.19 g/mol	Phe	F
15	Proline	C5H9NO2	115.13 g/mol	Pro	P
16	Serine	C3H7NO3	105.09 g/mol	Ser	S
17	Threonine	C4H9NO3	119.12 g/mol	Thr	T
18	Tryptophan	C11H12N2O2	204.23 g/mol	Trp	W
19	Tyrosine	C9H11NO3	181.19 g/mol	Tyr	Y
20	Valine	C5H11NO2	117.15 g/mol	Val	V

Short Facts about Amino Acids and Proteins

A bond formed between two atoms is an ionic bond.
Atoms that lose electrons become positively charged.
Atoms that gain electrons become negatively charged.
Atoms in charged states are called ions.
Plants absorb mineral salts as ions.
The intermolecular attraction between two molecules is called a hydrogen bond.
Organic molecules have carbon-based structures.
Amylose has unbranched chains; amylopectin has branched chains.
Glycogen is the main stored polysaccharide in animals (animal starch).
About 50% of the dry weight of an organism is protein.
All enzymes are proteins, but not all proteins are enzymes.
Ideal proteins are found in eggs and milk.
Animal protein is generally more useful than vegetable protein.
Lipids are esters of glycerol and fatty acids (e.g., oils and fats).
Essential fatty acids: Linoleic and linolenic acid.
Omega-3 and omega-6 fatty acids differ by the location of the double bond.
Steroids have carbon side chains on a four-carbon ring backbone; cholesterol is a steroid.
Enzymes are proteins that speed up reactions without being changed.
Zymase enzyme was discovered in yeast in 1897.
Enzymes with biochemical prosthetic groups are called co-enzymes.
Trypsin is used in cataract surgery.
DNA is cut by restriction enzymes and joined by ligase enzymes.