STPM Biology Structure of Cell and Organelle (Part 6)

Ribosome

Distribution:

• Found on the outer surface of rough endoplasmic reticulum (RER).
• Dispersed in the cytoplasm of eukaryotic and prokaryotic cells.
• Also found in mitochondria and chloroplast.

  

  Ribosome

   

   

Structure:

• Ribosomes are roughly spherical in shape.
• Ribosomes are the smallest cell organelles.
• Size: 20nm – 30nm (diameter).
• Ribosome is not bounded by any membrane.
• Ribosomes contains protein (50%) and RNA (50%).
• Ribosome consists of a small subunit and a large subunit.
• There are two types of ribosomes:
  • 70S(Svedberg centrifugation unit) ribosome, found in mitochondrion, chloroplast and prokaryotic cells.
  • 80S ribosome, slightly bigger than 70S ribosome, found in eukaryotic cells.

Functions:

• Serve as a site for protein synthesis.
• Synthesizes enzymes. All enzymes are proteins.