Lesson 2 of 14 · 6 min
Amino acids
NCERT §9.1
Kabir points at the dal simmering on the stove: its protein, he says, is built from a small set of molecules that all share the same backbone and differ in one spot only.
The lesson in notes
In short
From a biological point of view, the small organic compounds in tissue are grouped as amino acids, nucleotide bases, fatty acids and so on, rather than by chemical functional groups.
An amino acid carries an amino group and an acidic (carboxyl) group on the same carbon, the alpha carbon, so these are called alpha-amino acids.
They are substituted methanes: the four valencies of the alpha carbon hold a hydrogen, a carboxyl group, an amino group and a variable R group.
Many amino acids exist, but only twenty types occur in proteins. When R is a hydrogen the amino acid is glycine; a methyl group gives alanine; a hydroxy methyl group gives serine.
Their chemical and physical properties come from the amino, carboxyl and R groups. By the number of amino and carboxyl groups they are acidic (glutamic acid), basic (lysine) or neutral (valine). Tyrosine, phenylalanine and tryptophan are aromatic amino acids.
The –NH2 and –COOH groups can ionise, so the structure of an amino acid changes with the pH of the solution. The form carrying both a positive and a negative charge is the zwitterionic form.