Citric Acid Cycle

Question 1

Does the TCA occur under aerobic or anaerobic conditions?

Answer 1

aerobic

Question 2

Where does the citric acid cycle take place?

Answer 2

mitochondrial matrix

Question 3

What is the carbon source for the citric acid cycle?

Answer 3

acetyl CoA

Question 4

What does the oxidation of 2-carbon units in TCA produce?

Answer 4

3 NADH, 1 FADH2, 2 CO2, 1 GTP

Question 5

What do the electrons in the TCA do?

Answer 5

reduce oxygen and generate a proton gradient. This is then used to synthesize ATP.

Question 6

What is pyruvate from glycolysis converted into?

Answer 6

acetyl CoA.

Question 7

What is pyruvate converted into during anaerobic conditions?

Answer 7

lactate or ethanol.

Question 8

What does pyruvate do during aerobic conditions?

Answer 8

enters the mitochondria.

Question 9

What are the three major components of pyruvate dehydrogenase?

Answer 9

TPP (E1), Lipoamide (E2) and FAD (E3).

Question 10

What does TPP do?

Answer 10

oxidatively decarboxylates pyruvate.

Question 11

What does lipoamide do?

Answer 11

transfers acetyl group to CoA

Question 12

What does FAD do?

Answer 12

regenerates the oxidized form of lipoamide

Question 13

What is the first step of the TCA?

Answer 13

the conversion of pyruvate to acetyl CoA.

Question 14

The conversion of pyruvate to acetyl CoA involves what cofactors?

Answer 14

TPP, lipoic acid and FAD, as well as the stoichiometric cofactors CoA and NAD+

Question 15

The conversion of pyruvate to acetyl CoA involves what 3 steps?

Answer 15

decarboxylation, oxidation and transfer of an acetyl group to coenzyme A.

Question 16

Why are the three steps of the conversion of pyruvate to acetyl CoA coupled together?

Answer 16

To conserve energy to drive formation of NADH and CoA.

Question 17

What is the first step in the conversion of pyruvate to acetyl coa?

Answer 17

TPP + pyruvate = hydroxyethyl TPP

Question 18

what is the second step in the conversion of pyruvate to acetyl CoA?

Answer 18

hydroxyethyl TPP + lipamide -> acetyllipoamide (E1)

Question 19

What is the third step in the conversion of pyruvate to acetyl CoA?

Answer 19

coenzyme A + acetyllipoamide = acetyl CoA + Dihydrolipoamide (E2)

Question 20

In order to conduct another reaction, what must dihydrolipoamide be reconverted into?

Answer 20

lipoamide

Question 21

How is pyruvate dehydrogenase regulated?

Answer 21

allosterically and by reverse phosphorylation.

Question 22

What inactivates E2?

Answer 22

high acetyl CoA.

Question 23

The products of the TCA increase phosohrylation of what enzyme?

Answer 23

PDH.

Question 24

What enzyme phosphorylates PDH and makes it inactive?

Answer 24

kinase

Question 25

What enzyme dephosphorylates PDH and makes it active?

Answer 25

phosphatase

Question 26

ADP and pyruvate activate what enzyme regulator of PDH?

Answer 26

phosphatase; it works by activating PDH

Question 27

Does TCA or glycolysis produce more energy from glucose?

Answer 27

TCA

Question 28

What enzyme links glycolysis to the citric acid cycle.

Answer 28

pyruvate dehydrogenase

Question 29

The reaction of isocitrate to alpha-ketoglutarate produces what?

Answer 29

NADH; this is facilitated by isocitrate dehydrogenase.

Question 30

The reaction of alphaketoglutarate to succinyl coa produces what?

Answer 30

NADH; this is facilitated by alpha-ketoglutarate dehydrogenase complex

Question 31

The reactionof succinyl Coa to succinate produces what?

Answer 31

GTP; this is facilitated by succinyl CoA synthetase. This is also the only step that produces GTP.

Question 32

The reaction of succinate to fumarate produces what?

Answer 32

FADH2. This is facilitated by succinate dehydrogenase.

Question 33

The reaction of malate to oxaloacetate produces what?

Answer 33

NADH; this is facilitated by malate dehydrogenase.

Question 34

What is the role of succinate dehydrogenase?

Answer 34

It produces FADH2. It is not released from the enzyme, but electrons are passed directly to coenzyme q in the electron transport chain.

Question 35

What step of the the citric acid cycle is irreversible?

Answer 35

the conversion of pyruvate to acetyl CoA.

Question 36

If acetyl CoA is not used in the citric cycle, what can it also be used for?

Answer 36

lipid production.

Question 37

What dictates PDH activity?

Answer 37

energy charge. At high energy, PDH is negatively inhibited. At low energy, pyruvate and ADP activate PDH.

Question 38

Phosphatases are stimulated by what ion in order to initiate muscle contraction?

Answer 38

Calcium

Question 39

What activates fatty acid synthesis by activating phosphatases?

Answer 39

insulin; this increases the conversion of pyruvate to acetyl CoA.

Question 40

What is isocitrate dehydrogenase activated and inhibited by?

Answer 40

activated by ADP, inactivated by ATP and NADH.

Question 41

What is alpha ketoglutarate dehydrogenase inhibited by?

Answer 41

ATP, succinyl CoA and NADH.

Question 42

What is pyruvate dehydrogenase activated and inhibited by?

Answer 42

activated by ADP and pyruvate; inhibited by ATP, acetyl Coa and NADH.

Question 43

When energy needs are met, what are intermediates in the citric acid cycle used for?

Answer 43

the biosynthesis of other molecules.