Cell Membranes - The Basics

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  • Created by: tiacoles
  • Created on: 25-01-16 19:37

Membranes at the cell surface (plasma membrane)

  • Plasma membranes control which substances enter and leave the cell. They're partially permeable - they allow some molecules through but not others. 
  • Substances can move by diffusion, osmosis or active transport. They also allow recognition by other cells and cell communication.

Membranes within cells

  • Membranes around organelles divide the cell into different compartments. This makes different functions more efficient. (Mitochondria - Respiration)
  • The membranes of some organelles are folded, increasing their surface area and making chemical reactions more efficient (Mitochondria - Increased respiration)
  • Membranes can form vesicles to transport substances between different areas of the cell. (Proteins - Protein Synthesis)
  • Membranes within cells are also partially permeable. (RNA and DNA)

Membrane Structure

  • Consist of phospholipids, proteins and carbohydrates.
  • Fluid Mosaic Model : Phospholipid bilayer form a continuous, double layer.
  • Fluid: because the phospholipids are constantly moving.
  • Protein molecules are scattered through the bilayer like a mosaic.
  • Glycoproteins: Protein with a polysaccharide (carbohydrate chain) attached.
  • Glycolipids: Lipids with a polysaccharide chain attached. 
  • Cholesterol molecules are also present. 

Membrane Components


  • Barrier to dissolved substances (Hydrophilic Head - Hydrophobic Tail)
  • Arranged in a bilayer - heads face out to the water.
  • The centre is hydrophobic so ions


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