Permeability constant, active transport and water movement

Question 1

How does the cell membrane lipid bilayer act as a barrier?

Answer 1

it is impermeable to water and water soluble substances

Question 2

What are the ways of transport across the cell membrane?

Answer 2

diffusion

active transport

Question 3

What is the structure of aquaporins?

Answer 3

• comprise of 6 trans-membrane alpha-helices

- form tetramers in the membrane and each monomer acts as a water channel

Question 4

How is water uptake increased in the kidney epithelial cells?

Answer 4

ADH up-regulates AQP-2 channels in the epithelial cells

Question 5

What limits the rate of diffusion?

Answer 5

Vmax of the carrier protein

Question 6

What is primary active transport?

Answer 6

molecules are ‘pumped’ against an electrochemical gradient at the expense of ATP

Question 7

What is secondary active transport?

Answer 7

transport is driven by the energy stored in the electrochemical gradient of another molecule that was already pumped in/out of cell

Question 8

What is a symporter?

Answer 8

transport substances in the same direction as a ‘driver’ ion

Question 9

What is an antiporter?

Answer 9

transport substances in the opposite direction as a ‘driver’ ion

Question 10

What are the subunits of the sodium-potassium pump?

Answer 10

alpha

beta

Question 11

What are the functions of the sodium-potassium pump?

Answer 11

• important in controlling cell volume
• creates electrical gradient across the membrane
• responsible for secondary active transport