Ribosomes

[Electron Micrograph of ribosomes. The ribosomes operate in chains when translating a mRNA.]

The ribosome is plays a key role is the synthesis of protein. When the polypeptide chain is growing it must be kept aligned with the mRNA molecule so that each codon still hooks up with the tRNA molecule. After the addition of one amino acid the chain is moved down three codons. This is done using a large complex composed of protein and RNA, called the ribosome.

Ribosomes consist of one large unit and one small unit. Half of the eukaryotic ribosomal weight comes from RNA. The ribosome contains a groove that guides the polypeptide chain and another groove that holds the mRNA molecule.