Cell Membrane

• Why do we talk about heat loss of a mammal in terms of per gram of tissue?

  • Using per gram of tissue allows comparison as the mass of organisms varies
• What are some notes about the concentration gradient in terms of diffusion?

  • Must go from high to low
  • The greater the difference in concentration the faster diffusion / osmosis will occur
• How does a short diffusion pathway effect the diffusion rate?

  • Diffusion will occur quicker
• On a graph A increases rapidly then plateau and B increases steadily in a linear fashion - which is simple diffusion and which is facilitated diffusion and how do you know?

  • B is simple diffusion as the rate of transport and concentration difference across the membrane are linear in simple diffusion.
  • A is facilitated diffusion as facilitated diffusion can be limited by the number of available carrier proteins or channel proteins

  
• What is a hypotonic solution?

  • Has a low solute concentration and a high water potential
• What is a hypertonic solution?

  • A solution with a high solute concentration and a low water potential
• Uncontrolled cell divisions by mitosis can lead to the formation of tumours and cancer
• State 7 parts of the cell membrane structure

  A = Phospholipid bilayer

  B = Channel protein

  C = Carrier protein

  D = Glycolipid

  E = Glycoprotein

  F = Receptors

  G = Enzyme

  
• What is an aquaporin?

  • A small channel within the phospholipid bilayer that allows for the movement of charged water
• How do molecules get through these structures?

  • Carrier protein - Facilitated diffusion or active transport.
  • Channel protein -Facilitated diffusion.
  • Aquaporins -Water passes through via osmosis but not easily as it is not polar
• What is water potential?

  • The tendency of water to move from one area to another through osmosis.
• What is it water potential measured in?

  • kPa
• What does this sign mean? ψ

  • Water Potential
• What would the water potential of pure water be? (measurement)

  • Pure water would have a water potential of 0kPa
• Give some evidence that mitochondria / chloroplasts evolved from bacteria.

  • Circular DNA
  • Smaller ribosomes
  • No membrane bound organelles and are smaller in size compared to other cell organelles
• Prokaryotes:

  • Circular
  • Shorter
  • No intros
  • Not associated with histone proteins
• Eukaryotic:

  • Linear
  • Longer
  • Intros present
  • Associated with histone proteins
• What two things happen if you increase the surface area of a membrane in terms of fick's law?

  • An increase in the length that diffusion can take place across.
  • An increase in the available proteins needed for transport
• What will happen to our cells in an hypotonic solution and a hypertonic solution?

  • They will burst in a hypotonic solution
  • They will shrivel in a hypertonic solution
• What can we possibly do to treat cancer in terms of mitosis?

  We can target the cell cycle by either:

  • Preventing the synthesis of DNA resulting in no S phase.
  • Interfere with spindle formation preventing the separation of sister chromatids so that there is no anaphase
  • Cells can now no longer divide to increase in number.
• What does intrinsic and extrinsic mean in terms of movement through a membrane?

  • Intrinsic: It moves all the way through the bilayer
  • Extrinsic: It moves halfway through the bilayer
• What is Fick's law?

  • Diffusion rate = (SA x difference in concentration gradient) ÷ length of diffusion pathway
• What is the function of these membrane proteins?

  • Enzymes - for digesting proteins
  • Receptors - for binding to hormones (often glycoproteins; protein with a carbohydrate chain attached)
  • Cell recognition - antigens (can be proteins or glycoproteins) to recognise foreign cells
• What is meant by the ""fluid mosaic"" model of cell membrane structure?

  • Fluid - proteins can move around within the membrane by moving between phospholipids
  • Mosaic - Proteins sit within the membrane at intervals