Exam 3: Oxidative Phosphorylation

Question 1

In the electron transport chain, are protons pumped with or against their concentration gradient?

Answer 1

Against its gradient.

Question 2

What are three requirements of chemiosmotic energy coupling?

Answer 2

1. Membrane impermeable ions.
2. Membrane must contain proteins that couple the “downhill” flow of electrons in the ETC to the “uphill” flow to protons across the membrane.
3. Membrane must also contain a protein that couples the “downhill” flow of protons to the phosphorylation of ADP.

Question 3

Explain how Complex I accepts and donates electrons.

Answer 3

Complex I accepts two electrons from NADH but passes them on individually: one at a time.

Question 4

What are the reactants and products of Complex I?

Answer 4

NADH + Q + 5(H+) => (NAD+) + QH2 + 4(H+)

Question 5

What is the principle reaction that occurs in Complex II?

Answer 5

Succinate loses two hydrogens to FAD to form FADH2 and Fumarate.

Question 6

True or false, Complex II transports protons across the the membrane.

Answer 6

False.

Question 7

Iron-sulfur clusters, cytochrome bs, and cytochrome cs are contained in which complex?

Answer 7

Complex III.

Question 8

The Q cycle results in additional protons being added where?

Answer 8

The intermembrane space (IMS).

Question 9

How many molecules of QH2 become oxidized in the Q cycle?

Answer 9

Two molecules.

Question 10

In the Q cycle, ______ molecule(s) of Q become reduced using ___ electron(s) from QH2 oxidation.

Answer 10

…one …two …

Question 11

In Complex IV, how many subunits are there?

Answer 11

13 subunits.

Question 12

How many heme groups are in Complex IV and what are they called?

Answer 12

Two: a and a3.

Question 13

What are the two copper ions that are found in Complex IV and what do they do?

Answer 13

CuA accepts electrons from Cyt c and CuB is bonded to heme a3, forming a binuclear center that transfers electrons the the ultimate receiver, oxygen.

Question 14

Which complexes pump protons into the IMS?

Answer 14

Complex I and Complex IV.

Question 15

Which complexes add protons to the IMS?

Answer 15

Complex I, III, and IV.

Question 16

What is the role of iron-sulfur clusters?

Answer 16

They are single electron carriers.

Question 17

What are cytochromes?

Answer 17

Stationary or mobile proteins or subunits of complexes containing heme prosthetic groups.

Question 18

What are the roles of cytochrome c?

Answer 18

Cytochrome c is a mobile soluble protein, single electron carrier found in the IMS.

Question 19

Describe coenyme Q and its functions.

Answer 19

A lipid-soluble conjugate dicarbonyl compound that accepts one or two electrons at a time. Once reduced, it can carry protons and electrons through the membrane.

Question 20

From where to where does coenzyme Q transport electrons?

Answer 20

From either Complex I or II to Complex III.

Question 21

By what two methods can cytosolic NADH enter the ETC?

Answer 21

The malate-aspartate shuttle and glycerol 3-P shuttle.

Question 22

What are the two functional units of the mitochondrial ATP synthase complex?

Answer 22

F1 and F0.

Question 23

What is the function of F1?

Answer 23

F1 catalyzes the synthesis of ATP from ADP and Pi.

Question 24

What is the function of F0?

Answer 24

F0 is an integral membrane complex that transports protons from the IMS into the matrix, causing a rotation of the its central shaft subunit, from which energy is transferred into F1 to catalyze the phosphorylation of ADP.

Question 25

What is the primary form of regulation for oxidative phosphorylation?

Answer 25

Substrate availability: NADH or FADH2 and ADP and Pi.

Question 26

True or false, substrates are required for both electron transport and ATP synthesis.

Answer 26

True. Due the coupling of reactions, substrates are required for both.

Question 27

The accumulation of NADH acts to ______ the enzymes of glycolysis and TCA cycle.

Answer 27

…inhibit …

Question 28

What is IF1 and how does it work?

Answer 28

IF1 is the Inhibitor of F1, which works in the mitochondrial matrix to prevent hydrolysis of ATP during states of low [oxygen] by preventing ATPase from turning backwards.

Question 29

Is IF1 active at high or low pH?

Answer 29

Low pH, as it is encountered when electron transport is stalled due to low oxygen.