Electron Transport Chain and Chemioosmosis (Unit 2)

Question 1

What does the electron transport chain do?

Answer 1

Electron transport extracts potential energy in molecules from previous steps, uses it for ATP synthesis

Question 2

Where is the electron transport chain (ETC) located in eukaryotes?

Answer 2

The ETC is located in the inner mitochondrial membrane.

Question 3

What is the main function of the electron transport chain?

Answer 3

The ETC facilitates the transfer of electrons from NADH and FADH2 to O2.

Question 4

What are the four protein complexes involved in the ETC?

Answer 4

Complex I (NADH dehydrogenase), Complex II (succinate dehydrogenase), Complex III (cytochrome complex), and Complex IV (cytochrome oxidase).

Question 5

What is unique about Complex II in the ETC?

Answer 5

Complex II is a simple peripheral membrane protein, while the other three complexes consist of multiple proteins.

Question 6

What are the two mobile electron shuttles in the ETC, and what are their functions?

Answer 6

Ubiquinone, which shuttles electrons from Complex I/II to Complex III, and Cytochrome c, which transfers electrons from Complex III to Complex IV.

Question 7

How do the protein complexes in the ETC facilitate electron transfer?

Answer 7

Complexes I, III, and IV have increasing electronegativity along the chain and alternate between reduced and oxidized states to pull electrons from upstream molecules and donate them to more electronegative downstream molecules.

Question 8

What role does oxygen play in the ETC?

Answer 8

Oxygen is the final electron acceptor in the ETC. It pulls electrons away from Complex IV, reacts with hydrogen ions to form water, and drives the chain reaction of electron transfer.

Question 9

How many electrons does oxygen pull from the ETC, and what is produced as a result?

Answer 9

For every O2 molecule, four electrons are pulled from the ETC, creating two water molecules.

Question 10

Describe the electronegativity trend in the ETC.

Answer 10

The ETC components are organized from high to low free energy, with each component being more electronegative than the previous one. Oxygen is the most electronegative, while NADH is the least.

Question 11

How does free energy compare among ETC components?

Answer 11

Free energy decreases from NADH and FADH2 (highest) to Complex I, Complex II, Complex III, Complex IV, and finally to O2 (lowest).

Question 12

Why is NADH considered to have a lot of free energy?

Answer 12

NADH has a lot of free energy because it can be readily oxidized, releasing energy as it forms stronger bonds moving through the ETC.

Question 13

What is chemiosmosis?

Answer 13

Chemiosmosis is the process in which ATP is synthesized using the energy of an electrochemical gradient and the ATP synthase enzyme.

Question 14

Does the electron transport chain (ETC) itself create any ATP?

Answer 14

No, the ETC from NADH/FADH2 to O2 doesn’t itself create any ATP.

Question 15

: What is a proton gradient?

Answer 15

A proton gradient is the difference in proton (hydrogen ion) concentration across a membrane, which is a form of potential energy.

Question 16

How is the proton gradient formed in mitochondria?

Answer 16

Protons move across the inner mitochondrial membrane, causing a higher concentration in the intermembrane space than in the matrix.

Question 17

How do electrons flow through the ETC?

Answer 17

Electrons flow through the ETC with proton pumps in the inner mitochondrial membrane, and energy released from electron transport is used for proton pumping.

Question 18

What role does ubiquinone (UQ) play in the ETC?

Answer 18

UQ accepts electrons from Complex I/II, picks up protons from the matrix, moves through the membrane, donates electrons to Complex III, and releases protons into the intermembrane space.

Question 19

What is proton-motive force?

Answer 19

Proton-motive force is the force that moves protons due to a chemical gradient of protons across a membrane (electrochemical gradient).

Question 20

What creates the potential energy in a proton gradient?

Answer 20

The potential energy comes from the chemical gradient across the membrane and the electrostatic attraction of protons to the more negative interior of the matrix.

Question 21

How is chemiosmosis linked to oxidative phosphorylation?

Answer 21

Chemiosmosis is linked to the oxidation of energy-rich molecules by the ETC, which is known as oxidative phosphorylation. It relies on the large multi-protein complex, ATP synthase, unlike substrate-level phosphorylation during glycolysis and the citric acid cycle.

Question 22

What is ATP synthase?

Answer 22

ATP synthase is a molecular motor that spans the inner mitochondrial membrane. It has a basal unit embedded in the membrane connected to a headpiece by a stalk, with the headpiece extending into the mitochondrial matrix.

Question 23

How does ATP synthase work?

Answer 23

The basal unit of ATP synthase creates a channel for hydrogen ions. Proton motive force moves protons through this channel into the matrix, and the flow of protons powers ATP synthesis by the headpiece. ATP synthase doesn’t synthesize ATP directly but uses free energy from ATP hydrolysis to pump ions across the membrane.

Question 24

What happens when electron transport and ATP synthesis are uncoupled?

Answer 24

When electron transport and ATP synthesis are uncoupled, the energy released during transport is not converted to ATP but is instead released as thermal energy.

Question 25

How can the expression of uncoupling proteins affect the ETC?

Answer 25

The expression of uncoupling proteins provides an alternative pathway for protons to re-enter the matrix without producing ATP, releasing thermal energy. This is important for maintaining body temperature in hibernating mammals with high mitochondrial uncoupling protein expression.

Question 26

What are ionophores, and how do they function as uncouplers?

Answer 26

Ionophores are chemical compounds that act as uncouplers by forming channels across membranes through which ions can leak. This allows for high rates of electron transport but reduces ATP synthesis, and can be toxic.