Membrane Transporters/Ion Channels

Question 1

How does glucose accumulate in the cell if the transporter is allows glucose to go both ways?

Answer 1

Glucose is phosphorylated inside the cell.

Question 2

What comprises Kv NAv and Cav ion channels? Which have separate polypeptides? Which are linked as repeats?

Answer 2

4 membrane spanning domains.

Kv has separate domains.

Ca and Na are linked.

Question 3

How many alpha helices are contained in each domain of an ion channel protein?

Answer 3

6 alpha helices

Question 4

Which alpha helix is/are voltage sensitive?

Answer 4

S4

Contain either Lys or Arg at every third position.

Question 5

Which alpha helix is/are the selective filters?

Answer 5

S5+S6

Contain the “p loop”

Question 6

Why do patients with myotonia experience prolonged contraction after voluntary skeletal muscle contraction?

Answer 6

Defective CLC (Cl- channels).

Cl- is important for repolarization

Question 7

What is unique about the CLC channel?

Answer 7

They are dimers with 3 gates. one for each monomer cl channel and one to cover both channels.

Some of the CLCs are H/Cl exchanger.

Question 8

Dominant myotonia congentita effects which gate of the CLC protein?

Answer 8

Large gate that covers both channels.

Question 9

Which of the following is the most selective? Least selective?

Nav
Kv
nAchR
Cav

Answer 9

K+
nAchR

Ok-aaaaaa+ = great

nAchR (not your best ion channel)

Question 10

What are the differences in gates between Kv and Nav?

Answer 10

Kv has one activation gate that is opened and closed based on polarization.

Na has 2 gates. The activation gate and the inactivation gate. Activating the Nav channel expposes the binding site for the inactivation gate.

Question 11

What makes the inactivation gate?

Answer 11

The cytoplasmic III-IV linker.