Week 5 Bollough Lecture 7

Question 1

What is the equation used to calculate the membrane permeability of molecules?

Answer 1

permeabilities correlate with partition coefficients P = Dβ/L

a) P- membrane permeability
b) D- diffusion coefficient within membrane
c) β- water-membrane partition coefficient
d) L- membrane thickness

Question 2

Why do cells need to use active and passive transport?

Answer 2

For molecules or ions for which the membrane is impermeable or only weakly permeable, integral membrane proteins are required to facilitate their movement

Question 3

What is passive transport?

Answer 3

Passive transport- involves movement down a concentration gradient

Question 4

What is active transport?

Answer 4

Active transport- requires an energy input in order to move against the electro chemical gradient

Question 5

What is the generic architecture of a channel?

Answer 5

Hydrophobic interface protecting the pore from the hydrophobic membrane

a) Narrow pore with selectivity filter
b) Gate
c) Vestibule: area in pore which starts to narrow down

Question 6

What are aquaporins?

Answer 6

Water channels:

a) Increase the rate at which water flows through membranes
b) Typically, bidirectional
c) Very fast- 3 x 109 waters/second
d) Very selective, blocking protons and other ions
e) In the kidney, for example, water must be rapidly reabsorbed into the bloodstream after filtration

Question 7

What is the structure of aquaporins?

Answer 7

‘Hour glass’ structure

a) Helices tilted at 30° and twisted into a right-handed bundle
b) Has 2 half helices
i) which forma pseudo helix
ii) which forms the selectivity filter
c) Tetramer (4 monomers)
d) Each subunit has its own pore
e) Pores don’t necessarily work together