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Ribosome is a supramolecular amino acid polymerizing machine. Hey!. That’s my teacher’s definition of ribosome, the definition has stuck with me since he told me. But in case that definition is too complex. Here is a simpler definition of ribosome.


Ribosome is an important cell organelle located at the cytoplasm and around the endoplasmic reticulum which is responsible for processing genetic information on the mRNA into protein in a process known as translation.

Structure of Ribosome

The ribosome is a complex organelle made up of rRNA (ribosomal RNA) and ribosomal proteins. The rRNA composition of ribosome consist of two subunits; the large and the small unit, which fixes together to translate mRNA into polypeptide chain during translation process.

Ribosomes can be classified into two based on their structure:

  • Prokaryotic cells ribosome
  • Eukaryotic cells ribosome

Prokaryotic cell ribosome

Prokaryotes have 70S ribosome consist two subunits; 50S and 30S. Whereas the large subunit (50S) is composed of 23S (2904 nucleotides), 5S (120 nucleotides) rRNA units and 31 ribosomal proteins while the small subunit (30S) is composed of 16S (1542 nucleotides) and 21 ribosomal  proteins. ‘S – Sverdberg unit of sedimentation’

Eukaryotic cell ribosome

Eukaryotes have 80S ribosome which consist 60S and 40S subunits. The large subunit (60S) is composed of 28S (4718 nucleotides), 5.8S (160 nucleotides) rRNA and 49 ribosomal proteins. While the 40S (small subunit) is composed of (1874 nucleotides) rRNA and 33 ribosomal proteins.


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