Cell membranes and transport

HideShow resource information
  • Created by: zoolouise
  • Created on: 20-04-16 12:00

Cell membranes and transport

The cell membrane is a boundary which seperates the living cell from its non-living surroundings. It controls which substances can enter or leave the cell.

The structure of the membrane is described by Singer and Nicholson as a fluid mosaic:

  • Fluid because the indiviudal phospholipids can move about within the layer
  • Mosaic because the proteins appear dotted through the layer like a mosaic

The cell membrane is almost entirely made up of phospholipids and proteins. Phospholipids are made by replacing one of the fatty acids of a trigylceride with a phosphate group. A phospholipid is a polar molecule, with the phosphate head being hydrophillic and liphobic; the fatty acid tails are hydrophobic and lipophillic. Phospholipids therefore create a bilyar.

Singer and Nicholson put forward a model for the structure of the cell/plasma membrane and it states that:

  • There's a bimolecular phospholipid layer
  • Associated with the bilayer are a variety of proteins
  • Some of these proteins occur on just one layer of the membrane and are therefore called extrinsic proteins
  • Some proteins span both layers of the membrane and are called intrinsic proteins

Roles of various parts of the plasma membrane

1) Phospholipids

  • These create the bilayer and act as a barrier to most water-soluble substances
  • As their tails are non-polar it's also difficult for molecules or ions to pass through


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Cellular processes resources »