Protein Modification

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  • Protein Modifications
    • Intermediate modifications
      • Removal of targeting sequences - proteins will need to move
      • Folding; if denatured folding can reform, must be done correctly e.g. to hide hydrophobic regions. Misfolding can lead to aggregates
        • Abnormal processing of beta-amyloid can lead to amyloid plaques in alzheimers
        • Misfolding can lead to perversion (distortion). Abnormal cellular prion protein resists protease action BAD as it can convert normal protein to abnormal protein as it acts as an infectious agent
      • Chaperones; Assist folding. Used to be called heat shock proteins as produced in excess heat. e.g. HSP70 Provide environment and encase protein allowing correct folding
      • Polymer formation; new polypeptide chains may assemble with others and cofactors e.g. haemoglobin (2 alpha helices, 2  beta chains and accessory proteins (4 harm groups))
        • Tubulin dimers; alpha and beta tubulin not formed in isolation
    • Destruction of proteins
      • Incorrectly assembled proteins are destroyed. Tagged by ubiquitin which is attached to degradation signal e.g. expressed at inner regions of protein.
      • Addition of these (ubiquitinylated) causes destruction by the proteasome
    • Other modifications
      • Modificationsin the ER or cytosol e.g. lipidation of proteins.
      • Modificationsin the ER and golgi e.g. glycolysation of membrane bound and secreted proteins
      • Collagen is an example of a heavily modified protein
      • Lot's of different hormones can be made from same precursor
    • Effects of modifications
      • Sensitisation of notch
      • Phosphorylation of BAD (make it more or less likely that cells undergo suicide)


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