Active transport and ion channels (B23, 24)

Question 1

Why are channels not suited for active transport?

Answer 1

Channels don’t have a direct input of energy from ATP or other means
They rely on electrochemical gradients for the passive diffusion of molecules

Question 2

What are types of active transport?

Answer 2

1. Primary active transport- transporting one thing against conc. grad. usually with energy released from ATP hydrolysis or uses light
2. secondary active transport- transporting two things, can be unidirectional or bidirectional, usually transport one thing with conc. gradient and energy released from this used to transport other thing against conc.

Question 3

How fast are ion channels compared to ATP- powered pumps?

Answer 3

Ion channels much faster as down a conc. gradient (fascilitated transport)
Required to be fast for fast transmission such as in neurotransmission
ATP-powered pumps slow as coupled to ATP hydrolysis (Active transport)

Question 4

Explain alternating access/ simple allosteric model for membrane pumps

Answer 4

Interior cavity has high affinity to transported species, binds to site
Changes confirmation so that facing other side of membrane- this confirmation has lower affinity for substrate
Therefore even though there is a high conc of substrate, it has to be released into compartment because affinity is so low
Alters the potential energy of the substrate
Alternating access= access to both sides of membrane

Question 5

Explain Lac permease

Answer 5

1. Acidic amino acid is protonated (proton wants to go down gradient but can’t go through membrane so binds to protein first)
2. Changes binding site so lactose can bind
3. Confirmation change to close access to outside, stops leakage. Affinity for lactose greatly reduced and lactose released
4. Acidic amino acid deprotonated and proton released