Cell membranes

• The basic structure of the plasma membranes including

  cell surface membranes and the membranes around the cells organelles of eukaryotes are the same
• Membrane functions :

  
  

  • control entry and exit
  • internal support
  • isolate enzymes that might damage the cell
  • provide surfaces for reactions
  • separate organelles from cytoplasm so that specific metabolic reactions can happen
• The arrangement of the bi-layer of phospholipids , integrated proteins , glycoproteins and glycolipids is know as the fluid-mosaic model
• Phospholipid bi-layer forms a barrier to dissolved substances
• Phospholipi bI layer‘s centre is hydrophobic so it doesn’t allow water soluble substances through, but allows small , non polar molecules
• Intrinsic proteins - channel proteins and carrier proteins allow large molecules to pass through the membrane
• Peripheral proteins can act as receptors and allow the cell to detect chemicals released from other cells so that they can respond
• Temperature increases kinetic energy in phospholipids so they move faster making the bi layer less gel like and more fluid
• non-polar solvents such as alcohols or acetone can insert themselves into the bilayer
• Diffusion in membranes is a passive process which means it does not need a lot of energy
• factors that affect diffusion : concentration gradient, membrane thickness, surface area , temperature
• Proteins helps and facilitate the movement through the membrane for larger molecules
• Facilitated diffusion is a faster process
• Carrier proteins move large molecules across the membrane. Large molecules attach and the protein changes shape releasing the molecule into The other side of the membrane
• Channel proteins form pores for changed particles to diffuses through the membrane