Ribosomes

• In prokaryotes ribosomes are associated with the plasma membrane of the cell.
• They are about 15 nm by 20 nm in size.
• They are made of two subunits – 50S and 30S units.
• They together form 70S prokaryotic ribosomes. (S= sedimentation coefficient; a measure of density & size).

Function:

• Ribosomes are the site of translation (protein synthesis).
• Several ribosomes may attach to a single mRNA to form a chain called polyribosomes (polysome).
• Ribosomes of a polysome translate the mRNA into proteins.