Fluid Mosaic Model

• Cell membrane:

  • Acts as a protective barrier for the cell
  • Holds the components of the cell inside
  • Allows certain substances to enter and exit the cell in a controlled manner
• Cell membranes are described by scientists as the fluid mosaic model
• Cell membranes are composed of three main components:

  • Phospholipids
  • Cholesterol
  • Proteins
• Phospholipid bilayer:

  • Made of individual phospholipids
  • Arranged into two layers with heads pointing outwards and tails pointing inwards
• Phospholipids:

  • Head: phosphate molecule with a slight charge, attracted to water (hydrophilic)
  • Tails: fatty acids without a charge, repel water (hydrophobic)
  • Arrange in two rows in the cell membrane due to their attraction or repulsion to water
• Cholesterol:

  • Regulates the fluidity and permeability of the cell membrane
  • Causes phospholipids to stay closer together
• Proteins in the cell membrane:

  • Integral proteins: help transport large molecules across the membrane
  • Peripheral proteins: involved in communication and some transport
  • Glycoproteins: play a role in cell recognition by the immune system
• Integral proteins in the cell membrane can transport molecules:

  • Passively down their concentration gradient through protein channels
  • Actively against the gradient by protein pumps
• The fluidity of the cell membrane:

  • Allows the cell to move
  • Allows substances to move across the membrane easily
  • Maintains control over what substances enter and leave the cell