1.3 - Cell membranes and transport

• The membrane controls which substances pass in and out of the cell
• The cell membrane is made up almost entirely of proteins and phospholipids
• The phosphate head is a polar molecule (hydrophilic) and has an attraction for other polar molecules such as water
• The fatty acid end of the phospholipid, made up of two fatty acids, is non-polar(hydrophobic) and repels water
• The use of the electron microscope enabled Singer and Nicholson to put forward their theory called the fluid mosaic model in 1972
• Singer and Nicholson proposed that:

  • There is a bimolecular phospholipid layer
  • Within the bilayers is a variety of protein molecules
  • Some of the proteins only occur in one of the layers (extrinsic proteins)
  • Some of the proteins extend across both layers (intrinsic proteins)
  • The phospholipid layer is capable of movement
  • It is referred to as the "fluid mosaic" as the components are free to move
• Plasma refers to the fact that a hole can be made in the cell membrane and will be sealed immediately when object is removed
• Selectively permeable means that some substances can pass through the membrane but others cannot.
• Active transport requires energy from respiration
• Cholesterol is also found in animal cells.
• It fits between the phospholipid molecules,

  increasing the rigidity and stability of the membrane.
• Glycolipids are carbohydrates attached to lipids
• The main functions of the cell membrane include:

  Structural support

  Secreting chemicals

  Cell-to-cell recognition

  Taking up nutrients and other requirements