Cell membrane structure and transport

• The cell membrane...

  Controls the movement of substances in and out of the cell
• Function of phospholipids

  1. Phospholipids form bilayers
  2. The inner layer of phospholipids have their hydrophilic heads pointing in towards the cytoplasm
  3. The outer layer of phospholipids have their hydrophilic heads pointing outwards, interacting with the water surrounding the cell
  4. Hydrophobic tails of the 2 phospholipid layers point towards each other
  5. The phospholipid component of the membrane allows lipid-soluble molecules across, but not water soluble molecules
• Extrinsic proteins are found on either surface of the bilayer

  They form recognition sites, by identifying cells and receptor sites for hormone attachment
• Intrinsic proteins are found across both layers of the phospholipid bilayer

  • Carrier proteins transport water-soluble substances across
  • Others allow active transport of ions across by forming channels
• The fluid-mosaic model means that ...

  1. The phospholipid molecules within a layer can move relative to one another
  2. The proteins embedded in the bilayer vary in shape, size and pattern
• Cholesterol in the bilayer ...

  Makes the membrane more rigid and stable
• Glycoproteins and glycolipids in the bilayer ...

  Are involved in cell-to-cell recognition and some act as hormone receptors
• The carbohydrate layer around the membrane is called the

  glycocalyx
• The movement of molecules from an area of high concentration to an area of lower concentration down a concentration gradient is known as ...

  Diffusion
• A passive form of diffusion in which the molecule being transported binds to a protein in the membrane is known as ...

  facilitated diffusion
• When molecules are moved up a concentration gradient through proteins which expend energy to pump their substrates against a concentration gradient it is known as ...

  Active transport
• The movement of water molecules from a high concentration of water to a lower concentration of water through a semi-permeable membrane is known as ...

  osmosis
• The transport of a large amount of material out of the cell through vesicles

  Exocytosis
• The transport of a large amount of material into the cell

  Endocytosis
• When the cell takes in solid molecules it is known as

  phagocytosis
• When the cell takes in liquid molecules it is known as

  pinocytosis