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Ribosomes

Ribosomes
Introduction
These are tiny granular structures present in cytoplasm.
Discovery
Palade (1955) was the person, who first time discovered and studied them.
Production
New ribosomes are assembledin the nucleolus of the nucleus from where they are transported to the cytoplasm via the pores in the nuclear membrane.
Chemical Composition
Ribosomes are composed of almost an equal amount of:
  • RNA
  • Proteins
Due to presence of RNA and proteins, these are also called as ribonucleoprotein particles.
Existence
Ribosomes exist in two forms:
  • Freely dispersed in cytoplasm
  • Attached with the endoplasmic reticulum as tiny granules.
Structure
Each eukaryotic ribosome consist of two sub units:
  • Larger subunits sediment at 60S
  • Smaller subunits sediment at 40S
Two subunits on attachment, with each other form 80Sparticles (S = Svedberg unit which specifies sedimentation rate). This attachment is controlled by Mg2+ ions.
When many ribosomes get attached to the same stretch of mRNA they form a structure called ‘Polysome’.
Function
Ribosomes are involved in the synthesis of proteins.

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