Biological membranes

• The hydrophobic tails of phospholipids face away from water to avoid contact with it, while the hydrophilic heads face towards the water to interact with it.
• Phospholipids are amphiphilic molecules, meaning they have both hydrophobic (water-hating) and hydrophilic (water-loving) regions.
• The phospholipid bilayer is the main component of biological membranes
• the membrane is partially permeable membrane and the site if chemical reactions and cell communication
• fluid mosaic model


  the mixture and movement of the phospholipids, proteins, glycoproteins and glycolipids
• what do the extrinsic proteins do?


  provide mechanical support or they make glycoproteins and glycolipids. the function of them are cell recognition as receptors
• what do intrinsic proteins do?

  carrier or channel proteins which are involved in the transport of molecules across the membrane
• protein channels 


  form tubes that fill with water to enable water soluble ions to diffuse
• carrier proteins 


  they bind with other ions and larger molecules such as glucose and amino acids and change shape to transport them across them membrane
• what does cholesterol do?


  restricts lateral movement of other molecules in the membrane

  • makes the membrane less fluid at high temps and prevents water and dissolved ions from leaking out
• factors effecting membrane structure and permeability? 


  Temperature :

  • increase the kinetic energy of the phospholipids so they move even more
  • increases permeability and the structure can start to break
  • high temperatures denature carrier and channel proteins

  Solvents

  • dissolve the phospholipid bilayer
• simple diffusion 


  the net movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached (this does not require ATP)
• For molecules to diffuse across the membrane they must be lipid soluble and small
• facilitated diffusion


  A passive process, down the concentration gradient through proteins

  • the movement of ions and polar molecules
  • moved through protein channels and carrier proteins
• osmosis 


  high water potential moving to an area of low water potential across a partially permeable membrane
• isotonic 


  when the water potential of the solution is the same in the solution and the cell within the solution

  
• hypotonic 


  when the water potential of a solution is more positive than the cell

  
• hypertonic 


  when the water potential of a solution is more negative than the cell

  
• active transport 


  low concentration to a high concentration across the concentration gradient using ATP and a carrier protien
• endocytosis 


  type of active transport when a molecule forms a vesicle that can move through the cytoplasm
• endocytosis

  • cell membrane bends inwards around the molecule surrounding it to form a vesicle
  • vesicle pinches off and moves within the cytoplasm
  • this can be classes as phagocytosis when solid particle is being taken in
  • or pinocytosis when a liquid is being taken in
  • requires ATP for cell to engulf and change shape