Membrane Transport

Question 1

what are the two properties that influence whether a particle can permeate the PM without help?

Answer 1

• solubility of the particle in the lipid

- size of the particle

Question 2

what is simple diffusion

Answer 2

movement of molecules from an area of high concentration to low concentration (passive)

Question 3

what factors make up Fick’s Law of Diffusion?

Answer 3

1. the magnitude of the concentration gradient
2. the surface area of the membrane across which diffusion is taking place
3. the lipid solubility of the substance
4. the molecular weight of the substance
5. the distance through which diffusion must take place ie would take years for an oxygen particle to diffuse from the epidermis of the skin into the bloodstream

Question 4

what is the combination of a concentration gradient and an electrical gradient called

Answer 4

electrochemical gradient

• the electrochemical gradient influences the properties of the membrane

Question 5

what is osmosis

Answer 5

the net diffusion of water down its own conc. gradient

water moves to the area of higher solute conc.

Question 6

what is an aquaporin

Answer 6

a water channel

Question 7

what is osmolarity

Answer 7

the concentration of osmotically active particles present in a solution

Question 8

what is tonicity

Answer 8

the effect a solution has on cell volume

ie isotonic / hypertonic / hypotonic

Question 9

what are the three passive transport mechanisms

Answer 9

• diffusion down concentration gradients
• movement along electrical gradients
• osmosis

Question 10

what is carrier mediated transport

Answer 10

when a substance binds onto a specific carrier which undergoes a conformational change which then transports the substances across the membrane

Question 11

what are the three factors that influence the amount of substances transferred in carrier mediated transport

Answer 11

• specificity
• saturation
• competition

Question 12

what are the two types of carrier mediated transport

Answer 12

1. active transport (energy required)

2. facilitated diffusion (energy not required)

Question 13

what is the difference between primary and secondary active transport

Answer 13

primary splits ATP to get its energy
(think ATP)

secondary is coupled with the transfer of the ion that supplies the driving force ie doesnt split ATP
(ion coupled)

Question 14

what are some characteristics of the sodium/potassium (ATPase) pump ?

Answer 14

• primary active
• transports 3xNa out of the cell for every 2xK in

roles:
>helps establish the sodium and potassium gradients across the PM of all cells
>helps regulate cell volume by controlling conc. of solutes inside the cell
>the energy used to drive the pump indirectly serves as the energy source for secondary active transport

Question 15

what are the two mechanisms of secondary active transport

Answer 15

symport = co - transport (ie the solute and the driving force ion move in the same direction)

antiport = exchange or countertransport (the solute and the driving force ion move in opposite directions)

Question 16

what is vesicular transport

Answer 16

-active transport

can either be:

1. endocytosis - pinching off of membrane to engulf a substance
2. exocytosis - a vesicle fuses with the plasma membrane releasing its contents to the ECF (think secretion of enzymes)