2.5 Plasma membrane structure

• What are membranes?

  sheets of cells that cover the surface of every cell and most organelles
• The functions of membranes

  • keep cellular components in the cell
  • allow selected molecules in and out of the cell
  • isolating organelles from cytoplasm
  • allows cellular processes to happen separately
  • site for biochemical reactions
  • allowing a cell to change shape
  • site for receptors
• Phospholipids in membranes

  • Are amphipathic molecules
  • Hydrophobic region faces in
  • Hydrophilic region faces out

  
• What are membranes made up of?

  phospholipids, proteins, carbs and cholesterol
• What state are membranes in?

  fluid
• What is the purpose of membranes being fluid?

  proteins can move freely through the bilayer
• How can membranes be fluid?

  If they have phospholipids with unsaturated fatty acids
• What percentage of membrane mass do proteins make up?

  45%
• integral proteins


  • carriers or channels
  • help transport substances that cannot diffuse
• Extrinsic proteins


  -free on membrane surface/ bound to intrinsic protein
• What is the purpose of cholesterol in membranes?


  • controls membrane fluiditymore cholesterol= less fluid/ less permeable
  • binds to hydrophobic tails
  • rigid membrane
  • keeps membrane stable at body temp, otherwise cells would burst
  • particularly important in red blood cells, maintains their shape
• What molecules find it easiest to diffuse across cell membranes?

  • small/ non-polar
  • e.g. oxygen and CO2