biological membranes

    Cards (17)

    • describe the fluid mosaic model of membranes
      • fluid: phospholipid bilayer in which individual phospholipids can move; membrane has flexible shape.
      • mosaic: extrinsic and intrinsic proteins of different sizes and shapes are embedded.
    • explain the role of cholesterol and glycolipids in membranes
      • cholesterol: steroid molecule in some plasma membranes; connects phospholipids and reduces fluidity to make bilayer more stable.
      • glycolipids: cell signalling and cell recognition.
    • explain the functions of extrinsic and transmembrane proteins in membranes
      • binding sites/ receptors e.g for hormones and drugs.
      • antigens (glycoproteins)
      • bind cells together.
      • involved in cell signalling.
    • explain the functions of intrinsic transmembrane proteins in membranes
      • electron carriers (respiration/photosynthesis).
      • channel proteins (facilitated diffusion).
      • carrier proteins (facilitated diffusion/ active transport).
    • explain the functions of membranes within cells
      • provide internal transport system.
      • selectively permeable to regulate passage of molecules into/ out of organelles or within organelles.
      • provide reaction surface.
      • isolate organelles from cytoplasm for specific metabolic reactions.
    • explain the functions of the cell-surface membrane
      • isolates cytoplasm from extracellular environment.
      • selectively permeable to regulate transport of substances.
      • involved in cell signalling/ cell recognition.
    • 3 factors that affect membrane permeability
      • temperature: high temperature denatures membrane proteins/ phospholipid molecules have more kinetic energy and move further apart.
      • pH: changes tertiary structure of membrane proteins.
      • use of a solvent: may dissolve membrane.
    • outline how colorimetry could be used to investigate membrane permeability
      1. use plant tissue with soluble pigment in vacuole. tonoplast and cell-surface membrane disrupted = more permeability; pigment diffuses into solution.
      2. select colorimeter filter with complementary colour.
      3. use distilled water to set colorimeter to 0. measure absorbance/ % transmission value of solution.
      4. high absorbance/ low transmission = more pigment in solution.
    • osmosis
      water diffuses across semi-permeable membranes from an area of higher water potential to an area of lower water potential until a dynamic equilibrium is established.
    • what is water potential
      • pressure created by water molecules measured in kPa.
      • water potential of pure water at 25 celsius and 100kPa: 0.
      • more solute= water potential more negative.
    • how does osmosis affect plant and animal cells
      • osmosis INTO cell:
      > plant: protoplast swells = cell turgid.
      > animal: lysis.
      • osmosis OUT of cell:
      > plant: protoplast shrinks= cell flaccid.
      > animal: crenation.
    • simple diffusion
      • passive process requires no energy from ATP hydrolysis.
      • net movement of small, lipid-soluble molecules directly through the bilayer from an area of high concentration to an area of lower concentration (i.e down a concentration gradient).
    • facilitated diffusion
      • passive process.
      • specific channel or carrier proteins with complementary binding sites transport large and/ or polar molecules/ ions (not soluble in hydrophobic phospholipid tail) down concentration gradient.
    • explain how channel and carrier proteins work
      • channel: hydrophilic channels bind to specific ions= one side of the protein closes and the other opens.
      • carrier: binds to complementary molecule= conformational change releases molecule on other side of membrane; in facilitated diffusion, passive process; in active transport, requires energy from ATP hydrolysis.
    • active transport
      • active process: ATP hydrolysis releases phosphate group that binds to carrier protein, causing it to change shape.
      • specific carrier protein transports molecules/ ions from area of low concentration to area of higher concentration (i.e against concentration gradient).
    • exocytosis and endocytosis
      • active process
      • involved in bulk transport and transporting large particles
      • vesicles fuse with cell surface phospholipid membrane
    • 5 factors that affect the rate of diffusion
      • temperature
      • diffusion distance
      • surface area
      • size of molecule
      • difference in concentration (how steep the concentration gradient is)