lysosomes

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  • Lysosomes
    • Function
      • major source of intracellular digestion
      • cotain 40 hydrolytic enzymes e.g. proteases, nucleases
        • acid hydrolases
        • protected from own attack
          • membrane keeps enzymes out of cytosol
          • acid hydolases don't work at cellular pH 7.2
      • membrane bound organelle
        • pH of 5 is maintained by H+ pump in the membrane
          • uses ATP
    • How
      • enzymes are transported from ER where they were synthesised
      • digestion products are transported out of the lysosome by transporters in the membrane
      • acid hydrolases protected from digestion by high level of glycosylation
    • transport of hydrolases
      • signal peptide directs synthesis of lysosomal protein to the ER
        • N-linked glycosylation
      • signal patch directs phosphorylation of terminal mannose
      • M6P binds to receptors on hydrolases (luminal)
      • also to adaptin on the cytosol side
      • packaging them into clathrin coated vesicles
      • vesicle binds with late endosome
        • acidic pH causes M6P to disassociate
        • signal in the tail of M6P signals it to return to the golgi
      • phosphate removed from mannose to ensure isn't transported back to golgi
      • hydrolases digest macromolecues, endosome becomes lysosome
    • transport from lysosome
      • passive diffusion
      • membrane transporters
        • digestion products transported out by transporters in the membrane
      • endocytic pathway
        • lysosomal secretion allows for break down of indigetable debris
        • mainly when under stress
        • defects can cause albiinism
    • peroxisomes
      • bags of oxidative enzymes
      • sites of oxidative reactions
      • beta-oxidation
        • acetyl coenzyme a-exported to the cytoplasm for synthesis reactions and mitochondria for ATP production
      • synthesis reactions
        • e.g. first step in production of phosolipids in the myelin sheath
      • protein import
        • marked by c terminal signal
        • proteins fully folded when imported
        • use ATP

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