Ribosomes and Inclusion Bodies

This section covers two internal features of prokaryotic cells: the ribosomes, where proteins are built, and the inclusion bodies, where reserve materials are stored.

Ribosomes

In prokaryotes, ribosomes are associated with the plasma membrane of the cell. Each ribosome measures about 15 nanometres by 20 nanometres and is built from two subunits:

• a larger 50S subunit and
• a smaller 30S subunit.

When these two subunits come together, they form the 70S prokaryotic ribosome. Ribosomes are the site of protein synthesis.

Polysomes

Several ribosomes can attach to a single mRNA molecule, forming a chain called a polyribosome or polysome. All the ribosomes of a polysome translate that one mRNA into protein at the same time.

Inclusion bodies

Reserve materials in prokaryotic cells are stored in the cytoplasm as inclusion bodies. An important point about them is that they are not bound by any membrane — they lie free in the cytoplasm. Examples include: …