Protein control: (Vuister) Membrane and transport 2

Question 1

Gibbs free energy values in the various transport processes?

Answer 1

Passive transport, DeltaG < 0
- e.g. diffusion, osmosis

Fascillitated transport, DeltaG < 0
- usually involves channels

Active transport, DeltaG > 0
- e.g. pumps, symporters

Question 2

Properties of K+ channel?

Answer 2

Facilitating transporter for K+
Ubiquitous, 4 types, found in excitable cells
Symmetric tetramer
Central pore

Highly selective for K+
- due to size of pore, energy of dehydration

Question 3

General structure of a channel?

Answer 3

Extracellular funnel

Selectivity filter

Central cavity

activation gate

Question 4

Explain the selectivity of aquaporin channels and mechanism of h20 transport

Answer 4

Channel allows single file transport of H20

• aided via positively charge residues

Allows transport of H20
Not allow transport of H30+

Dipole and h20 ‘flip’ at centre of channel caused by electrostatic forces, thereby breaking the alternative donor-acceptor arrangement that is necessary for proton translocation