cell membrane

• what is the function of the cell membrane

  it forms a boundary between the cytoplasm and the internal environment

  it allows different conditions to be established inside and outside the cell

  it controls the movement of substances in and out of the cell
• what is a phospholipid bilayer

  a phosphate head with fatty acid tails

  the phosphate head is hydrophilic and the fatty acid tails are hydrophobic

  they are polar due to a difference in charge throughout the molecule
• describe the function of a phospholipid bilayer

  allows lipid soluble substances to enter or leave

  prevents water soluble substances from entering or leaving

  membrane is flexible and self sealing
• membrane proteins

  transmembrane proteins- span all the way across

  peripheral proteins- do not span the entire membrane
• what are the two types of transmembrane proteins 


  channel- they have a hollow core that allows substances to diffuse through. They are a water filled pore that allows the diffusion of water soluble ions

  carrier- conformational change to allow substances in or out. They bind ions or other molecules (glucose/amino acids), this causes a conformational change so that the molecule can move across the membrane using facilitated diffusion
• cholesterol

  adds strength to the membrane

  hydrophobic- helps to prevent loss of water and dissolved ions

  pulls fatty acid tails together- limits movement but still allows fluidity
• glycolipids (adhesion molecules)

  carbohydrate covalently bonded to a lipid

  cell recognition

  blood types

  cell to cell adhesion
• glycoproteins

  cell surface receptors for hormones and neurotransmitters

  cell to cell adhesion

  cell recognition
• permeability


  most molecules do not diffuse across the membrane because:

  they are too large to pass through channels

  not lipid soluble

  charged (polar)

  repelled by protein channels due to the charge on them
• fluid mosaic model

  fluid- phospholipid layers can move and it allows flexibility (the ability to change shape and gain/lose molecules)

  mosaic- proteins vary in shape, size and pattern