Carbohydrates, lipids, proteins and nucleic acids

Proteins are biopolymers built from 20 kinds of amino acids. Each amino acid consists of an amino group (–NH₂), a carboxyl group (–COOH) and a characteristic radical; neighbouring amino acids are joined by peptide bonds, with one water molecule released per bond. The primary structure of a protein is the sequence of amino acids (set by the information in DNA), the secondary is a helix, the tertiary a globule, and the quaternary the association of several polypeptides (for example haemoglobin). High temperature or chemicals can destroy the natural shape – denaturation. Proteins perform structural, enzymatic, transport, protective, hormonal, movement and energy functions. The monomer of nucleic acids is the nucleotide, made of a nitrogenous base, a pentose and a phosphate group. DNA is a double-stranded helix: A–T (two hydrogen bonds), G–C (three hydrogen bonds); by Chargaff’s rule A = T and G = C. RNA is single-stranded, contains ribose and uracil, and occurs as mRNA, tRNA and rRNA. ATP consists of adenine, ribose and three phosphate groups, and takes part in storing and passing on energy.