Membrane structure

• Phospholipid bilayer 


  Bond between glycerol and a fatty acid is called an ester bond
• The hydrophilic head of the phospholipids are attracted to water, while the hydrophobic tails repel it.
• Proteins can be found on both sides of the cell membrane
• Integral proteins are embedded within the lipid bilayer
• Peripheral proteins are attached to integral proteins or the outer surface of the membrane by weak bonds such as ionic bonds
• Head of a phospholipid 


  Structure: A phosphate group bonded to a glycerol

  Hydrophilic: ”water loving” meaning the head attracts to water molecules
• Tails of a phospholipid 


  Structure: two fatty acids (hydrocarbon chain)

  Hydrophobic- “water fearing“ the tails do not attract to water
• Phospholipids have hydrophilic heads and hydrophobic tails.
• The hydrophilic heads face outwards, while the hydrophobic tails face inward towards one another.
• Nonpolar substances can pass through the cell membrane more easily due to their lack of polarity.
• This creates a barrier that prevents polar substances from passing through easily.
• Polar substances cannot pass through the cell membrane because they are attracted to both polar ends of the lipid bilayer.
• Phospholipids in water 


  When exposed to water they from one of two structures:

  a micelle or a bilayer
• Phospholipids in a membrane 


  -act as a barrier( controls what enters and exits the cells)

  -the smaller and les polar a molecule the faster it will diffuse across the membranes

  -O2 and CO2 diffuse rapidly as they are non polar

  -charged particles are unlikely to diffuse across a membrane
• Cholesterol is an important component of animal cell membranes as it helps maintain fluidity at low temperatures by preventing the fatty acid chains from packing too closely together.
• Bilayers - flat sheets where the nonpolar tails form the interior and the polar heads form the exterior
• Micelles - spherical shape with phosphate head groups on the outside
• Cholesterol also plays a role in regulating the permeability of the membrane
• Integral proteins

  Span the whole width of a membrane
• Integral Carrier protein 


  Help transport substances such as ions, sugars and amino acids that can’t diffuse across the membrane but are vital to cells functioning
• Integral channel proteins 


  Tunnels allowing molecules to pass through carrier proteins

  Changes shape to allow molecules to pass through
• Peripheral proteins 


  Make enzyme reactions faster and more efficient

  Communicating with neighbouring cells
• Glycolipids and glycoproteins 


  Both are a result of glycosylation
• Functions of glycolipids and glycoprotein 


  Attachment points

  Cell identification