2.3 Cell Membrane

• Why do we talk about heat loss of a mamal 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, how do you know? [4]

  B is simple diffusion as the rate of transport and concentration difference across the membrane is 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
• On a graph the line starts of level then rapidly increases, plateau then quickly decreases.

  Describe and explain this prokaryotic population growth curve. [3]

  As bacteria start to asexually reproduce via binary fission the graph rapidly increases ⁽¹⁾ till it stabilises due to limiting factors like nutrients ⁽¹⁾. The decrease is due to the death of bacteria which is caused by increased CO2 or acidity ⁽¹⁾.
• 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 the water molecule is polar.
• ○ What is water potential?

  ○ What is it measured in?

  ○ What does this sign mean? ψ

  ○ What would the water potential of pure water be? (measurement)

  ○ The tendency of water to move from one area to another through osmosis.

  ○ Kilopascals (kPa).

  ○ Water potential.

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

  They have: circular DNA, smaller ribosomes, no membrane bound organelles and are smaller in size compared to other cell organelles
• Assign these properties to either prokaryotics or eurokaryotics:

  ○Linear or circular (loops).

  ○Shorter or Longer.

  ○No intros or intros present.

  ○Not associated with histone proteins or associated with histone protiens.

  ○Prokaryotics:

  Circular, Shorter, No intros, Not associated with histone proteins.

  ○Eurokaryotics:

  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 and 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 = (surface area x difference in concentration gradient) ÷ length of diffusion pathway
• What is the function of these membrane proteins?

  ○ Enzymes.

  ○ Receptors.

  ○ Cell recognition.

  ○ 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
• Facilitated diffusion occurs because hydrophilic substances cannot pass through the hydrophobic phospholipid bilayer; therefore they are helped through the membrane by channel or carrier proteins.
• In which part of the membrane does osmosis occur?

  In the phospholipid bilayer.
• Which part of the cell surface membrane is used for membrane stability and affects fluidity?

  Cholesterol.
• Suggest and explain two ways in which the cell-surface membranes of the cells lining the uterus may be adapted to allow for the rapid transport of nutrients.

  There are lots of protein channels within the membrane for facilitated diffusion.

  Microvilli provide a large surface area to provide many places for diffusion to take place.