Blog / Role And Structure Of Ribosomes

Role and structure of ribosomes

Written by Shubhi Khandelwal on Feb 26, 2020

A ribosome is a complex macromolecule composed of rRNAs and many distinct polypeptides. In eukaryotes, the synthesis and assembly of rRNAs occur in the nucleolus. It is involved in the synthesis of proteins.

Ribosomes exist in the cytoplasm in prokaryotes and in the cytoplasm and on rough endoplasmic reticulum membranes in eukaryotes. Mitochondria and chloroplasts also have their own ribosomes, and these look more similar to prokaryotic ribosomes (and have similar drug sensitivities) than the cytoplasmic ribosomes. Ribosomes dissociate into large and small subunits when they are not synthesizing proteins and reassociate during the initiation of translation. Prokaryotic cells have a 30S small subunit and a 50S large subunit, for a total of 70S when assembled.  Mammalian or eukaryotic ribosomes have a small 40S subunit and a large 60S subunit, for a total of 80S. The small subunit is responsible for binding the mRNA template, whereas the large subunit sequentially binds tRNAs.


Key Points

  • Ribosomes are present in the nucleus, cytoplasm, and organelles like chloroplast and mitochondria.
  • In prokaryotic cells, 70 S ribosomes are present with subunits 30S and 50S.
  • In eukaryotic cells, 80 S ribosomes are present with subunits 40S and 60S.
  • Ribosomes are the factory of protein synthesis.

Key Terms

  • ribosome: protein/mRNA complexes found in all cells that are involved in the production of proteins by translating messenger RNA
  • Translation: Synthesis of proteins from mRNA

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