Question

What kind(s) of organisms make polyribosomes

Answer 1

A polyribosome (or polysome or ergasome) is a group of ribosomes bound to an mRNA molecule like “beads” on a “thread”. It consists of a complex of an mRNA molecule and two or more ribosomes that act to translate mRNA instructions into polypeptides. Polysomes are formed during the elongation phase when ribosomes and elongation factors synthesize the encoded polypeptide. Multiple ribosomes move along the coding region of mRNA, creating a polysome. The ability of multiple ribosomes to function on an mRNA molecule explains the limited abundance of mRNA in the cell. Polyribosome structure differs between prokaryotic polysomes, eukaryotic polysomes.

            Polyribosomes are found prokaryotes and eukaryotes both either free in the cytoplasm or can attach to the endoplasmic reticulum (ER) and the nucleus membranes. They are attached to rough endoplasmic reticulum surface and the outer membrane of the nucleus in eukaryotes. As prokaryotes lack nuclear membrane and membrane bound organelles, thus polyribosomes are found free in cytoplasm in prokaryotes.

Three forms of polyribosomes are:

– Free form

– Cytoskeletal bound

– Membrane bound.

Polysomes are present in archaea, but not much is known about the structure.