Passive Transport Through Membranes

Question 1

What are the 7 factors that affect the diffusion rate?

Answer 1

1. Magnitude of the concentration gradient (larger=faster)
2. Size of the molecule (larger=slower)
3. Surface area: Volume ratio (shape) (higher=faster)
4. Solubility of the solute (nonpolaer=soluble)
5. Temperature (higher=faster)
6. Density of the solvent (higher=slower)
7. Distance to the destination (longer=slower)

Question 2

What are two important features for facilitated diffusion ion channels? What do these allow for?

Answer 2

1. Selectivity filters
2. Gate

These allow for size and shape complementarity

Question 3

How many selectivity filters does the K+ channel have? What 2 interactions do they use to allow for selection?

Answer 3

K+ has 2 selectivity filters

Hydrogen bonds
Electrostatic Repulsions

Question 4

What 3 ways to gate an ion channel?

Answer 4

1. Voltage
2. Ligand (intracellular or extracellular)
3. Stress (mechanically gated)

Question 5

What 5 ion channels work together to contract your muscles?

Answer 5

1. Depolarization opens Voltage-Gated Ca2+ channels
2. Exocytosed acetylcholine opens Ligand-Gated Na+ channels
3. Local depolarization opens adjacent Voltage-Gated Na+ channels
4. As the depolarization spreads, Voltage-Gated Ca2+ channels open
5. Coupled Ca2+ release channels embedded in the SR open

The two main types of ion channels used in this pathway are voltage and ligand-gated

Question 6

What are 2 examples of facilitated diffusion ion channels?

Answer 6

Gap junctions:

• Allow cytoplasm sharing
• Always open (No gate)
• No specificity filter/selectivity

Aquaporins:

• Lets water through, but not ions
• Still always open
• Has a little selectivity

Question 7

What kinds of forces allow for aquaporins to let water through?

Answer 7

Adhesion and cohesion