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