GOLGI BODY

• Golgi apparatus


  A complex network of smooth membrane enclosed organelle which helps in collection, packaging, distribution and secretion of biomolecules
• Golgi apparatus


  • Occurs in all eukaryotic cells except male gametes of bryophytes and pteridophytes, mature sieve tubes, some fungal cells, and mature sperms and RBCs of animals
  • Absent in prokaryotic cells
• Distribution of Golgi apparatus in animal cells


  • Single and localized near nucleus and often close to the centrosome
  • Diffused in form of two or more interconnected units in most invertebrate cells
• Distribution of Golgi apparatus in plant cells


  • Consists of many independent units called dictyosomes or Golgi bodies or Golgi stacks
  • Number highly variable - from one in simple alga like Micromonas to 25000 in rhizoidal cell of aquatic alga chara
  • A liver cell may have up to 50 dictyosomes
• Dictyosome


  Each individual subunit of the Golgi apparatus in plant cells
• Structure of Golgi apparatus


  • Extremely dynamic and pleomorphic structure due to variable shape and form in different cell types
  • Consists of a stack of 3-10 flattened sacs or cisternae with a complex irregular network of tubules, vesicles and vacuoles on the outer edges
  • Adjacent cisternae separated by an intercisternal space of 10-30 nm containing protein cross-links that hold the cisternae together
  • Cisternae may be flat or curved to give a definite polarity to the Golgi body
• Polarity of Golgi body

  • Cis face (convex) facing towards nucleus
  • Trans face (concave) facing towards plasma membrane and containing a tubular reticulum called trans Golgi network (TGN)
• Membrane thickness


  • Membranes of maturing face are thicker (7-8µm)
  • Membranes of forming face are thinner (about 4 µm)
• Golgi vesicles


  • Small vesicles (20-80 µn in diameter) associated with the Golgi body
  • Transport proteins and lipids between the cisternae and tubules
• Transport of materials in Golgi


  1. Transitional vesicles pinched off from the rough ER fuse with the cis face

  2. Transport or shuttle vesicles keep budding off from the cisternal edges and tubules to transport materials between the cisternae in cis-to-trans direction

  3. Secretary vesicles derived from TGN carry glycoproteins, glycolipids and polysaccharides to different destinations in the cell or outside the cell
• Secretary vesicles


  • Smooth secretary vesicles
  • Coated vesicles covered by a basketlike network of protein complex consisting of clathrin triskelions
  • Larger secretary vesicles called Golgian vacuoles, some of which function as lysosomes
• Constitutive secretion


  Secretory products are produced and released continuously
• Regulated secretion


  Secretory products are released in response to specific stimuli