Question

1. Ion channels contain a selectivity filter that (choose best answer)

a) selects for positively charged ions by virtue of the negatively charged amino acids lining the pore, but allows similar ions through, like Na+ and K+.

b) selects for size of ions based on interactions with the ion transport protein.

c) binds with extreme sensitivity to their specific ion, akin to an enzyme forming a specific binding site for a substrate.

d) selects for ions based on size and charge due to the width of the channel and charge of amino acids lining the channel.

2. What is the role of K+ -gated ion channels in an action potential?

a) They do not have a role in action potentials

b) They provide the energy for the sodium potassium pump to reestablish resting potential

c) They lead to the action potential reaching its highest state of cell depolarization

d) They help reverse the action potential by repolarizing the cell.

3. Which of the following has the lowest electron affinity

a) Cytochrome c reductase complex

b) NADH dehydrogenase complex

c) Oxygen

d) Cytochrome c oxidase complex

4. The low redox potential of NADHmeans that is has a

a) High electron affinity

b) Very stable bond

c) Low free energy

d) Tendency give up electrons

Answer 1

Q1. Ans is option D.

The selectivity of an ion channel depends on the size of an ion (e.g - whether any water shell is present around the ion or not) and interaction of the ion with the amino acid linking the channel. As for example potassium channel allow the passage of potassium ion, which does not have any water shell and it interacts with the carbonyl group lining the channel wall.

2. Ans is D.

After depolarisation reaches its maximum height, potassium channel opens fully and allowes the movement of potassium ion from the interior of the cell to the exterior, bringing down the positive ion gradient. Thus, the voltage difference starts to coming down and the cell starts repolarise. As the potassium channel is slow responders, these channels remain open for longer time, causing bringing down the potential to a value lower than the resting memb potential. This is known as hyperpolarization.
3. Ans is option - B.

According to the redox potential, the higher the redox potential, the higher the electron affinity of the compound.

so, NADH dehydrogenase has the lowest redox potential and has the ability to transfer electron quickly... means lowest affinity to electron.

4. Ans is option D.
'lower redox potential means that the compound ha the lowest affinity towards the electron and transfers the electron to the next carrier quickly.
'Such, it has a strong tendacy to give up electrons.