Lecture 2

Question 1

Define “kinetic and thermal energy” explain how these relate to molecular movement

Answer 1

• Kinetic energy is the energy of motion
• The average kinetic energy of the molecules in an object is the object’s thermal energy (temperature)
• Random molecular movement = thermal kinetic energy

Question 2

Define diffusion, osmosis and how they relate to semipermeable membranes

Answer 2

• Diffusion is the movement of particles from a region of high conc. to a region of low conc.
• Osmosis is the movement of a solvent through a semipermeable membrane from a less concentrated solution into a more concentrated one

Question 3

How is osmotic pressure generated?

Answer 3

• Because of concentration differences, water will accumulate on one side of the membrane creating a higher pressure
• Effective osmotic pressure = osmotic pressure*reflection coefficient (σ)
• σ refers to ease with which a solute permeates a membrane: (1 = impermeable, 0 = completely permeable)

Question 4

Describe diffusion

Answer 4

• Energy independent
• Factors affecting rate of diffusion:
  
  • Proportional to conc. difference across membrane
  • Membrane electric potential (Nernst potential)
  • Pressure difference
    Diffusion across biphospholipid layer:
  • O2, CO2, Nitrogen and alcohols can diffuse readily

Question 5

Factors that increase permeability

Answer 5

• Increase in oil/water partition coefficient
• Decrease in size of solute
• Decrease in membrane thickness

Question 6

Equation for measuring diffusion

Answer 6

J= -PA(C1-C2)

- (Look at powerpoint slide for example)

Question 7

Describe facilitated diffusion

Answer 7

• Requires carrier proteins
  
  • Occurs down an electrochemical gradient
  • A uniporter has binding sites that are alternately available on either side of the membrane
  • Carrier mediated transport establishes stereo specificity
  • Structurally similar solutes may compete for transport sites on carrier molecules
  • Used by glucose, amino acids
  • Vmax (Refer to figure 4-7) - finite # of transport molecules

Question 8

Types of protein channels

Answer 8

• Non-gated channels:
  
  • Aquaporins
  • K+ channels with selectivity filters (carbonyl oxygens)
  • Na+ channels
• Gated channels
  
  • Voltage gated channels
  • Ligand gated channels

Question 9

Describe K+ channel selectivity filter

Answer 9

• K+ ions are larger than Na+ ions, however only K+ ions must pass through, the selectivity filter composed of carbonyl oxygens dehydrate the K+ allowing them to pass however the Na+ having a smaller radius are not dehydrated from carbonyl oxygens thus staying hydrated and too large to pass through pore

Question 10

Define active transport

Answer 10

• Movement of particles against a gradient (going against entropy)
• Requires metabolic energy and carrier proteins

Question 11

Types of active transport

Answer 11

• Primary active transport
  
  • Energy is derived directly from breakdown of ATP
  • Utilizes ATPases transporters
• Secondary transport
  
  • Energy is derived secondarily from conc. differences of molecular or ionic substances created originally by primary active transport
  • Utilizes multiporters (symporters/antiporters)
  • One of the solutes moves down its electrochemical gradient while another moves up
  • Na+ is more concentrated outside cell, movement down into cell generates the energy needed to transport another substance against its gradient

Question 12

Explain how body compartment volumes can be altered

Answer 12

• Active transport across a layer of cells

- Refer to figure 4-15