Ribosomes

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Ribosomes are minute particles consisting of RNA and associated proteins that function to produce proteins. Proteins are needed for many cellular functions like repairing,damage or directing chemical processes. Ribosomes can be found floating within the cytoplasm or attached to the endoplasmic reticulum.

Ribosome's Size

Ribosomes comprise of two subunits that are composed and function as one to translate the mRNA into a polypeptide chain and protein synthesis.They vary in size between prokaryotic cells and eukaryotic cells.

The prokaryotic ribosome is comprised of a 30s (Svedberg) subunit and a 50s (Svedberg) subunit meaning 70s for the entire organelle equal to the molecular weight of 2.7×106 Daltons. And Eukaryotic cell comprise of a 40s (Svedberg) subunit and a 60s (Svedberg) subunit which means 80s (Svedberg) for the entire organelle which is equal to the molecular weight of 4×106 Daltons.

  • The ribosome word is derived – ‘ribo’ from ribonucleic acid and ‘somes’ from the Greek word ‘soma’ which means ‘body’.
  • Ribosomes are tiny spheroidal dense particles (of 150 to 200 A0 diameters) that are primarily found in most prokaryotic and eukaryotic.
  • They are sites of protein synthesis.
  • They are structures containing approximately equal amounts of RNA and proteins and serve as a molecules involved in protein synthesis.
  • The ribosomes occur in cells, both prokaryotic and eukaryotic cells.
  • In prokaryotic cells, the ribosomes often occur freely in the cytoplasm.
  • In eukaryotic cells, the ribosomes either occur freely in the cytoplasm or remain attached to the outer surface of the membrane of the endoplasmic reticulum.
  • The location of the ribosomes in a cell determines what kind of protein it makes.
  • If the ribosomes are floating freely throughout the cell, it will make proteins that will be utilized within the cell itself.
  • When ribosomes are attached to the endoplasmic reticulum, it is referred to as rough endoplasmic reticulum or rough ER.
  • Proteins made on the rough ER are used for usage inside the cell or outside the cell.
  • The number of ribosomes in a cell depends on the activity of the cell. 
  • On average in a mammalian cell, there can be about 10 million ribosomes.


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