Structures inside membrane

• describe the structure of cholesterol

  • Hydroxyl group on head
  • Carbon rings
  • Non-polar tail
• what does the hydroxyl group do on a cholesterol?

  makes the cholesterol head polar and hydrophilic - attracted to the phosphate heads on the periphery of the membrane
• how do carbon rings in cholesterol affect its classification?

  its not classed as a fat or an oil, cholesterol is a steroid
• what role do the non-polar tails play on a cholesterol?

  make it hydrophobic which is attracted to the hydrophobic tails of phospholipids in the centre of the membrane
• what is the average width of a membrane?

  7-9 nm
• what are the roles of a phospholipid?

  • acts as a barrier of polar molecules
  • they are arranged in a double layer forming a hydrophobic core
  • hydrophilic heads can interact with water, so they form both the inner and outer surface of a membrane sandwiching the fatty acids as cells normally live in aqueous environments (outside cells and usually inside too)
• what are intrinsic proteins?

  • transmembrane proteins that are embedded in the plasma membrane, spanning across both bilayers
  • have amino acids with hydrophobic R-groups on external surface, which interact with the hydrophobic core of the membrane, keeping them in place
  • channel proteins and carrier proteins (involved in transport across membrane)
• what are extrinsic proteins?

  • peripheral proteins - present in one side of the bilayer
  • normally have hydrophilic R-groups on their outer surfaces and interact with the polar heads of the phospholipids or with the intrinsic proteins
  • can be present in either layers and some move between layers
• what are glycoproteins?

  • intrinsic proteins
  • embedded in cell-surface membrane with attached carbohydrate (sugar) chains of varying shape and length
  • they play a role in cell adhesion and as receptors for chemical signalling
• what are glycolipids?

  • lipids with attached carbohydrate chains
  • these molecules are called cell markers or antigens and can be recognised by the cells of the immune system as self (of organism) or non-self (of cell belonging to other organism)
• what is cholesterol?

  • a lipid with a hydrophilic end (head) and a hydrophobic end (tail)
  • regulates/modifies membrane fluidity - adds stability to membranes without making them too rigid (prevents phospholipids from grouping too closely together and crystallising)
  • is positioned between phospholipids with hydrophilic end interacting with heads and hydrophobic end interacting with tails, pulling them close together