Transport Across Membranes

    Cards (29)

    • The fluid mosaic model describes the surface appearance of the cell membrane due to its intrinsic and extrinsic proteins and fluid phospholipid bilayer
    • The membrane of a vacuole is called the tonoplast
    • Membranes control the diffusion of substances as well as play a role in cell recognition
    • Simple lipid diffusion can occur through the phospholipid bilayer if molecules are small and uncharged or lipid soluble
    • The main components of a cell membrane are channel and carrier proteins, phospholipids and cholesterol
    • The role of cholesterol in a cell membrane is to keep phospholipids from drifting too close together and drifting apart when warm
    • Phospholipid tails point inwards as they are non polar and hydrophobic, phospholipid heads point outwards as they are polar and hydrophillic
    • Intrinsic proteins span the whole plasma membrane, extrinsic proteins exist on the membrane surface
    • Intrinsic protein examples are carrier and channel proteins
    • Extrinsic protein examples are glycolipids and glycoproteins which act as cell identifiers
    • Active transport is the transport of molecules against a concentration gradient using ATP
    • Facilitated diffusion is movement of molecules via a protein carrier or channel without the use of ATP down a concentration gradient
    • Hypotonic is where the outside solution has a higher water potential than the inside
    • Hypertonic is where the outer solution has a lower water potential than the inside
    • Isotonic is where water potentials are equal, there may be dynamic equilibrium
    • Osmosis is the passive transport of water down a water potential gradient across a selectively permeable membrane
    • In channel proteins, ions dissolved in water are transported across the membrane, the channel protein is lined with hydrophilic groups
    • A solution with a higher water potential has more free water molecules (not associated with an ion)
    • In incipient plasmolysis, half of the plant cells are plasmolysed so the solutions are now isotonic
    • Red blood cells become haemolysed when they shrivel
    • Animal cells have no cell wall so are susceptible to osmotic lysis
    • Rate of diffusion is proportional to ( surface area x difference in concentration ) divided by thickness of exchange surface
    • Carrier proteins have a complimentary shape to a specific molecule which it will bind to and then undergo a conformational change of shape to transport it across the membrane
    • There is a limit to the rate of facilitated diffusion as carrier proteins can become saturated
    • In co transport, the sodium potassium antiport pumps sodium ions out of the cell and potassium ions into the cell
    • When sodium ion concentration inside the columnar cell is low it creates a concentration gradient between the columnar epithelium and the lumen
    • Sodium ions in the lumen diffuse across the cell membrane into the columnar epithelial cell bringing a glucose or amino acid with them
    • The glucose concentration in the columnar cell increases creating a concentration gradient, glucose diffuses by facilitated diffusion into the bloodstream
    • Cholesterol is a steroid