Examples of Semi autonomous Organelles

Semi autonomous organelles are organelles with DNA. In eukaryotic cells, mitochondrion and chloroplast are semi autonomous organelles as it posses its own DNA. Majority of proteins needed for these organelles are coded by DNA or genes in the nucleus. Only few proteins are coded by organellar DNA. That is why these organelles are called semi autonomous organelles.
Semi autonomous organelles mitochondriona and chloroplast

Mitochondrion
Location: Few to 1000 in cytoplasm, more number in active cells.
Shape and Size: Sausage shaped, approximately 500x 200 nm
Structure:
  • Double membrane bound organelle
  • Outer membrane with porin proteins (transport proteins) and is permeable
  • Inner membrane with infoldings called cristae, less permeable, presence of cardiolipin
  • Mitochondrial matrix: proteins 65-70%, lipids 25-30%, 0.5% RNA and circular DNA molecule
  • Mitochondrial DNA is called as mt DNA which is double stranded circular DNA located in the matrix
  • Microscopic observation: Janus Green stain-stains living mitochondria greenish blue.
Function:
·         Called as the “power house of the cell”
  • Inner membrane: site of oxidative phosphorylation and electron transport and associated ATP production.
  • Central matrix: site of citric acid cycle and fatty acid break down and mt DNA codes some mitochondrial proteins, but majority are coded by nuclear genes.
Chloroplast
Location: In cytoplasm of green plant cells.
Shape and Size: Generally Disc shaped about 5,000 x 10,000 nm in diameter.
Structure:
  • Double membrane bound organelle
  • Flattened membranous sac like structure that is stacked is called as Grana. Each individual unit is called as thylakoid. Thylakoid membrane is the site of light reaction.
  • The fluid filled matrix is called stroma.
  • Chloroplast DNA is called as cp DNA which is double stranded circular DNA located in the stroma
Function:
· Photosynthesis and photorespiration
· Grana: Light reaction or synthesis of ATP and NADPH
· Stroma: Dark reaction or CO2 fixation using energy  (ATP and NADPH) synthesised during light reaction
· Thylakoid lumen: H2O splitting complex.
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