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Physical Properties of Biological Membranes definitions

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  • Lipid Bilayer
    Double-layered structure forming biological membranes, composed mainly of phospholipids, providing a barrier and matrix for diffusion.
  • Lateral Diffusion
    Rapid, uncatalyzed movement of lipids side-to-side within the same layer of a membrane, maintaining sheet composition.
  • Transverse Diffusion
    Slow, enzyme-catalyzed transfer of lipids between membrane layers, also known as flip-flop, altering sheet composition.
  • Flippase
    Membrane enzyme requiring ATP, moves specific lipids from the outer to the inner sheet, maintaining asymmetry.
  • Floppase
    Membrane enzyme requiring ATP, transfers lipids from the inner to the outer sheet, contributing to membrane diversity.
  • Scramblase
    Membrane enzyme facilitating bidirectional lipid movement down concentration gradients, does not require ATP.
  • Transition Temperature
    Specific point where membrane shifts from gel-like rigidity to fluidity, affecting permeability and viscosity.
  • Membrane Fluidity
    Degree of flexibility and movement within a membrane, influenced by temperature, lipid composition, and embedded molecules.
  • Permeability
    Ease with which substances cross a membrane, increases with fluidity and decreases in gel-like states.
  • Fatty Acid Chain Length
    Number of carbon atoms in phospholipid tails; longer chains raise transition temperature and reduce fluidity.
  • Saturation
    Extent of double bonds in fatty acid chains; more double bonds lower transition temperature and increase fluidity.
  • Phospholipid
    Major membrane component with hydrophilic head and hydrophobic tails, forming the bilayer structure.
  • Cholesterol
    Membrane-embedded molecule modulating fluidity and permeability, stabilizing membrane structure.
  • Gel-like State
    Rigid, less permeable membrane condition occurring below transition temperature, restricting substance movement.
  • ATP
    Energy molecule required by certain membrane enzymes to catalyze lipid movement between bilayer sheets.