Amino acids

Amino acids:

Amino acids are compounds that contain amine and carboxylic groups. Each unit of amino acid (monomer) contains positive and negative group thus the amine group and the carboxylic group form what is known as a zwitterion (dipolar ion or internal salt). In the zwitterion, the carboxylic group loses hydrogen ion (COO^-) to the amine group (NH₃⁺).

The formation of the internal salt gives the amino acid the distinguished properties of salt such as; forming crystalline solids and having high melting points. The solubility of amino acids is associated with the R side chain. More polar side chain results in more soluble amino acids. Still, amino acids are insoluble in nonpolar organic solvents such as; ether and carbon tetra-chloride (hydrocarbon solvents). Amino acids are classified into polar and non-polar according to the R side chain:

Amino acid 

a. polar amino acids:  

There are 20 natural amino acids that protein is driven form. The polar amino acids are divided into;

a. Acidic side chain amino acids such as; Aspartic acid, glutamic acid, cysteine, and tyrosine. Those amino acid contain side chains that end with COO^-, OH or SH groups.

b. Basic side chains amino acids are; arginine, histidine, and lysine.

c. Unionized amino acids: Asparagine, glutamine, serine, and threonine.

For non-polar amino acids, there are 8 amino acids: alanine, glycine, isoleucine, leucine, methionine, phenylalanine, proline, tryptophan, and valine

The 20 natural amino acids divided into two groups polar and non-polar amino acids

From the above figure, it can be seen that there are some amino acids with aromatic side chains (phenylalanine and tyrosine) and others with only aliphatic side chains (valine and leucine).

Except for glycine all amino acids contain chiral carbon atom (carbon atom that is connected to different groups). The natural amino acids all contain alpha (α) carbon atom.

The amino group in 19 of the 20 amino acids is a primary (connected to two hydrogen and one carbon atoms) except for proline it is secondary (connected to two carbon and one hydrogen atoms).

The polymerization of amino acids by condensation reaction results in either peptide (short series of amino acids) or longer chains which are proteins. Amino acids that contain alpha group their polymerization result in the formation of beta sheets of α-helix.

Next: Amino acids reactions