Ribosomes are protein synthesizing nano machines present in all types of cells. Ribosomes are ribonucleoprotein protein complexes (RNA+ Protein) made up of two subunits a larger subunit and a smaller subunit.
  • Occur as free ribosomes in cytoplasm
  • Bound to rough endoplasmic reticulam (RER)
  • Bound to nuclear outer membrane
Function: Protein synthesis
80S vs 70S Ribosomes
Eukaryotic Ribosomes 80S
Prokaryotic Ribosomes 70S
Present in Eukaryotes or all higher organisms. Present in Prokaryotes (bacterium), Mitochondrion and chloroplast.
Consists of 2 subunits, 60S and 40S. Consists of 2 subunits, 50S and 30S.
The 80S ribosomes are composed of 40% RNA and 60% proteins. The 70S ribosomes are composed of 60% RNA and 40% proteins.
The 60S subunit contains three rRNAs (28S, 5.8S and 5S) complexed with ~49 proteins The 50S subunit contains two rRNAs (23S and 5S) complexed with ~34 proteins.
The 40S subunit contains 18S rRNAs complexed with ~33 proteins. The 30S subunit contains 16S rRNAs complexed with ~21 proteins.

Note: The Svedberg unit (S) is used as a measuring unit for sedimentation speed which is related to the size, shape and density of the particle.
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