BACTERIAL RIBOSOMES

 RIBOSOMES

—  Bacterial cells have thousands of Ribosomes in their cytoplasm, which gives cytoplasm a grainy appearance.

—  Number of Ribosomes in bacterial cell varies from 10000 to 15000.

—  Chemically, a Ribosome is a combination of a special type of RNA called ribosomal RNA, or rRNA (about 60 %), and protein (40 %).

—  Ribosomes are the sites of Protein synthesis (Translation) in cells.

—  The Ribosomes are held together by mRNA and form Polyribosomes or Polysomes.  

—  All Ribosomes are composed of two sub-units, each of which is composed of polypeptides and molecules of RNA called ribosomal RNA (rRNA). The sub-units of Prokaryotic 70S ribosomes are a smaller 30S sub-unit and a larger 50S sub-unit.

ü  The 30S sub-unit contains Polypeptides and a single rRNA molecule

ü  The 50S sub-unit has Polypeptides and two rRNA molecules.

—  The letter S refers to Svedberg units, which indicate the relative rate of sedimentation during ultra-high-speed centrifugation.

—  Several Antibiotics work by inhibiting Protein synthesis on prokaryotic Ribosomes.

ü  Antibiotics such as Streptomycin and Gentamicin attach to the 30S sub-unit and interfere with Protein synthesis.

ü  Antibiotics such as Erythromycin and Chloramphenicol, interfere with protein synthesis by attaching to the 50S sub-unit.

ü  Antibiotics such as Erythromycin and Chloramphenicol, interfere with protein synthesis by attaching to the 50S sub-unit.