• Ribosomes are granular structures first observed under the electron microscope, and they appear as dense particles.  
  • They are not surrounded by any membrane. 
  • Ribosomes are composed of ribonucleic acid (RNA) and proteins. They are the cellular machinery responsible for protein synthesis, where the information stored in the genetic code is used to produce proteins. 
  • Ribosome Types:

There are two main types of ribosomes found in cells:

1. Eukaryotic Ribosomes:

Eukaryotic cells have 80S ribosomes, consisting of two subunits: a larger subunit (60S) and a smaller subunit (40S). 

2. Prokaryotic Ribosomes: Prokaryotic cells have 70S ribosomes, consisting of a larger subunit (50S) and a smaller subunit (30S). 

  • Svedberg's Unit (S): The designation 'S' in 80S and 70S ribosomes stands for the sedimentation coefficient, which is indirectly a measure of density and size. 
  • Ribosomes play a fundamental role in the translation of genetic information from the mRNA (messenger RNA) into functional proteins within the cell.  
  • Both 70S and 80S ribosomes are composed of two subunits and are involved in protein synthesis, but their size and composition vary between prokaryotic and eukaryotic cells.