Polysomes (polyribosomes)

The process of translation takes place relatively slowly. This means that in fact several ribosomes attach to a mRNA at the same time. Theses are called polysomes. This allows one mRNA to be used to produce many polypeptides. Often polysomes and the mRNA form an almost circular arrangement. In the diagram below the polypeptides are growing as the ribosomes move around the mRNA in a clockwise direction.

Primary protein structure

These are simply long chain polypeptides joined by peptide bonds.

The primary structure is determined by the number and sequence of the amino acids that make up the polypeptide.

An example could be

Glucagon a 29-amino acid polypeptide. Its primary structure in humans is:

NH2-His-Ser-Gln-Gly-Thr-Phe-Thr-Ser-Asp-Tyr-Ser-Lys-Tyr-Leu-Asp-Ser- Arg-Arg-Ala-Gln-Asp-Phe-Val-Gln-Trp-Leu- Met-Asn-Thr-COOH.