CELL MEMBRANE

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Membrane structure

  • Membranes are composed mainly of lipids and proteins
  • Membrane lipids
    • Phosphoglycerides are the major
    • sphingolipids
    • cholesterol
  • Phospholipids
    • form a bilayer,
    • hydrophilic head groups interact with water on both the extracellular and intracellular surfaces
    • hydrophobic fatty acyl chains in the central portion of the membrane.
  • Peripheral proteins are attached at the periphery of the membrane
  • Integral proteins span from one side of the membrane to the other.
  • Carbohydrates
    • attached to proteins and lipids on the exterior side of the cell membrane
    • They extend into the extracellular space.
  • Lipids and proteins
    • can diffuse laterally within the plane of the membrane.
    • Therefore, the membrane is termed ‘‘fluid mosaic.’’
  • Membrane function
    • Membranes serve as barriers that separate the contents of a cell from the external environment or the contents of individual organelles from the remainder of the cell.
    • The proteins in the cell membrane have many functions.
      • transport of substances across the membrane.
      • enzymes that catalyze biochemical reactions.
      • function as receptors that bind external ligands such as hormones or growth factors.
      • mediators that aid the ligand–receptor complex in triggering a sequence of events (e.g., G proteins) known as signal transduction;
        • second messengers (e.g., cAMP ) that alter metabolism are produced inside the cell.
      • cystic fibrosis transmembrane regulator (CFTR)
        • results in cystic fibrosis (CF)
        • a chloride ion channel found on cell membranes.
        • the most common mutation of which is the loss of a phenylalanine residue at position 508, known as the DF508 mutation
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