Krebs Cycle and Oxidative Phosphorylation

Question 1

Where does the Krebs cycle take place?

Answer 1

the mitochondria

Question 2

Within the TCA cycle there are two key electron transporters. What are their names in oxidized and reduced form?

Answer 2

Oxidized: NAD+ and FAD+

Reduced: NADH and FADH

Question 3

There is a molecule that both begins the citric acid cycle and is regenerated at the end. What is it?

Answer 3

Oxaloacetate

Question 4

What role does pyruvate dehydrogenase play in the krebs cycle?

Answer 4

This enzyme catalyzes the breakdown of pyruvate into acetyl-CoA, starting the krebs cycle rxns

Question 5

Why would calcium be considered an activator for pyruvate dehydrogenase?

Answer 5

Ca2+ release during exercise comes from your muscles contracting (aka using energy) so your body will want to breakdown glucose to meet the body’s demands for energy

Question 6

Why would ATP be considered an inhibitor for pyruvate dehydrogenase?

Answer 6

Product inhibition. ATP is a product of the TCA cycle so a buildup of ATP signals the mitochondria to halt the breakdown of acetyl-CoA

Question 7

If NADH or FADH2 were taken out of the electron transport chain, which one would have a greater negative effect on ATP production?

Answer 7

NADH; it is the higher energy molecule and generates 3 ATP compared to the 2 ATP for FADH2

Question 8

Within the mitochondria, is the inside or outside more positive and why?

Answer 8

The outside of the mitochondria is more positive because the mitochondrial matrix is actively pumping protons into the inter-membrane space

Question 9

If there is such a strong positive charge outside the mito. matrix and a strong negative charge within the mito. matrix, then why don’t the protons just migrate back into the mitochondria matrix?

Answer 9

The mitochondrial matrix is impermeable to protons. The only way they can cross back over is through active transport via ATP synthase which generates the energy needed for ATP formation.

Question 10

Within the 4 main steps of cellular respiration (glycolysis, pyruvate to acetyl-CoA, TCA cycle, and oxidative phosphorylation) which step generates the most ATP?

Answer 10

Oxidative phosphorylation

Question 11

What happens if we run out of oxygen during cellular respiration?

Answer 11

Fermentation will take the place of the TCA cycle and oxidative phophorylation

Question 12

If the body can make ATP with or without oxygen, then why do we need oxygen in the first place?

Answer 12

Oxygen allows the TCA cycle and oxidative phosphorylation to occur which is more efficient than fermentation. Fermentation also results in buildup of lactic acid

Question 13

High cellular concentrations of what molecule would inhibit the entry of pyruvate into the citric acid cycle?

A. NADH
B. ADP
C. glucose
D. FAD+

Answer 13

A. NADH (only one of these that’s a product of the TCA cycle)

Question 14

What powers the ATP synthase rotary motor?

Answer 14

the proton gradient

Question 15

What cellular conditions favor increased activity of the electron transport chain and oxidative phosphorylation?

A. High ATP concentrations
B. High FADH2 concentrations
C. High ADP concentrations
D. NADPH concentrations

Answer 15

High ADP concentrations

Question 16

With respect to their relative pH, how do the cytosol, intermembrane space of the mitochondria, and the mitochondrial matrix compare?

Answer 16

pH of mitochondrial matrix (very basic due to proton gradient) > pH of cytosol (neutral) > pH of intermembrane space (very acidic due to proton gradient)

Question 17

What products of glucose oxidation are essential for oxidative phosphorylation?

A. pyruvate
B. NADH & FADH2
C. NAD+ & FAD+

Answer 17

NADH and FADH2

Question 18

What is the effect of increased levels of hydrogen ions in the intermembrane space of the mitochondria?

Answer 18

Increased ATP production

Question 19

What is the process called by which protons from the intermembrane space move back into the mitochondria?

Answer 19

Chemi-osmosis

Question 20

How do the electron transport chain and chemiosmosis affect the acidity of the intermembrane space and mitochondrial matrix?

Answer 20

The electron transport chain and chemiosmosis increase the acidity of intermembrane space and mitochondrial matrix, respectively

Question 21

Predict the outcome of a mitochondrial membrane that is more permeable to hydrogen ions than normal.

Answer 21

A leaky membrane reduces the gradient of hydrogen, thus less ATP is formed, increasing the levels of inorganic phosphate and ADP in the mitochondrial matrix

Question 22

Cyanide is a poison that inhibits the electron transport chain by creating a strong and stable bond with Fe–Cu center in cytochrome C oxidase (complex IV). What is the immediate consequence cyanide poisoning?

Answer 22

Prevents the reduction of oxygen

Question 23

Which electron carrier would have the greatest negative impact on ATP production during oxidative phosphorylation if its production was inhibited?

Answer 23

NADH because it’s higher energy and more abundant than FADH2

Question 24

What would occur if all available hydrogen ions were used by ATP synthase?

A. it would raise the pH of the intermembrane space
B. it would drop the pH of the intermembrane space

Answer 24

It would increase the pH of the mito intermembrane space

Question 25

The proton pump in oxidative phosphorylation creates a gradient of protons across the inner mitochondrial membrane. What kind of energy is generated with such gradient?

A. Potential
B. Kinetic
C. Electric
D. Chemical

Answer 25

A. potential energy (protons pushed into the intermembrane space are “very ready” to return to the matrix meaning they have a lot of potential energy)

Question 26

Disruption of which process will have the greatest impact on the number of electron carriers used by the electron transport chain?

A. glycolysis
B. krebs cycle
C. gluconeogenesis
D. fermentation

Answer 26

the krebs cycle, it generates the most NADH/FADH2