Chapter 19: Harvesting Electrons from the Cycle

Question 1

The citric acid cycle is the final common pathway for…

Answer 1

The oxidation of fuel molecules

Question 2

The citric acid cycle oxidizes ______ to ______.

Answer 2

Acetyl CoA to CO₂

Question 3

The function of the citric acid cycle is to __________ from carbon fuels in form of NADH and FADH₂

Answer 3

Harvest high-energy electrons

Question 4

The citric acid cycle is strictly….

Answer 4

Aerobic

Question 5

Citric acid cycle consists of 2 stages:

Answer 5

1. Oxidation of the 2 carbon atoms to 2 CO2
2. Regeneration of oxaloacetate.

Question 6

Both stages of the citric acid cycle generate…

Answer 6

High-energy electrons that are used in oxidative phosphorylation.

Question 7

Stage1 of Citric Acid Cycle:

Answer 7

Acetyl CoA + Oxaloacetate –> Citryl CoA (Int) –> Citrate

Question 8

Citrate synthase exhibits…

Answer 8

Induced fit

*Leads to formation of the binding site for acetyl CoA

Question 9

Step 2 of Citric Acid Cycle:

Answer 9

Citrate –> cis-Aconitate (Int) –> Isocitrate

Question 10

_______ catalyzes the formation of isocitrate from citrate

Answer 10

Aconitase

Question 11

Step 3 of Citric Acid Cycle

Answer 11

Isocitrate –> Oxalosuccinate (unstable int) –> a-Ketoglutarate

*First reaction where CO₂ and NADH produced

Question 12

_________ catalyzes the oxidative decarboxylation of isocitrate to a-ketoglutarate

Answer 12

Isocitrate dehydrogenase

Question 13

Step 4 of Citric Acid Cycle

Answer 13

a-Ketoglutarate –> Succinyl CoA

*Produces CO₂ and NADH

Question 14

_________ catalyzes the formation of succinyl CoA by oxidative decarboxylation of a-ketoglutarate.

Answer 14

a-ketoglutarate dehydrogenase complex

Question 15

Stage 2: Step 5 of Citric Acid Cycle

Answer 15

Succinyl CoA –> Succinate + GTP

*High phosphoryl potential

Question 16

_______ catalyzes the cleavage of succinyl CoA to form succinate and GTP.

Answer 16

Succinyl CoA synthetase

Question 17

Step 6 of Citric Acid Cycle

Answer 17

Succinate –> Fumarate

by succinate dehydrogenase

*produces FADH₂

Question 18

Step 7 of Citric Acid Cycle

Answer 18

Fumarate –> Malate

by fumarase

Question 19

Step 8 of Citric Acid Cycle

Answer 19

Malate –> Oxaloacetate + NADH

by malate dehydrogenase

Question 20

The citric acid cycle produces

Answer 20

• High-transfer potential electrons
• GTP
• CO₂

Question 21

The NADH and FADH₂ formed in the citric acid cycle are oxidized by…

Answer 21

The electron transport chain

Question 22

How many ATP generated per NADH? per FADH₂?

Answer 22

2. 5 ATP per NADH
3. 5 ATP per FADH₂

Question 23

1 Acetyl unit generates _____ molecules of ATP.

Answer 23

10

Question 24

Citric acid cycle is the __________ for aerobic oxidation of fuel molecules and is a source of _______.

Answer 24

Final common pathway; building blocks

Question 25

The key control points in the citric acid cycle are the reactions catalyzed by...

Answer 25

Isocitrate dehydrogenase and α-ketoglutarate dehydrogenase.

Question 26

Control Point 1: Isocitrate dehydrogenase is allosterically activated by ____ and inhibited by \_\_\_\_.

Answer 26

Activated by ADP Inhibited by NADH and ATP

Question 27

Control Point 2: a-Ketoglutarate dehydrogenase is inhibited by \_\_\_\_\_\_\_.

Answer 27

* Succinyl CoA * NADH * ATP

Question 28

Rate of citric acid cycle is reduced when the cell has...

Answer 28

High levels of ATP and NADH.

Question 29

Many of the components of the citric acid cycle are...

Answer 29

Precursors for biosynthesis of key biomolecules.

Question 30

Intermediates of the Citric Acid Cycle must be replinished. Replenishing reactions are called...

Answer 30

Anaplerotic reactions.

Question 31

An example of anaplerotic reaction is the carboxylation of...

Answer 31

Pyruvate by pyruvate carboxylase

Question 32

Defects in succinate dehydrogenase, fumarase or pyruvate dehydrogenase kinase can contribute to the development of \_\_\_\_\_.

Answer 32

Cancer

Question 33

These defects contribute to use of aerobic glycolysis (Warburg effect) by cancer cells leading to production of \_\_\_\_\_.

Answer 33

Lactate

Question 34

The glyoxylate cycle is similar to the citric acid cycle but bypasses the \_\_\_\_\_\_\_\_\_, allowing the synthesis of carbohydrates from fats.

Answer 34

Two decarboxylation steps

Question 35

The glyoxylate cycle has two specific enzymes that are not present in the citric acid cycle:

Answer 35

Isocitrate lyase Malate synthase

Question 36

The glyoxylate cycle has 2 acetyl CoA enter per cycle and leave as \_\_\_\_\_.

Answer 36

Succinate (Which can then be converted to glucose)

Question 37

During the Citric Acid Cycle ATP or GTP is produced in the conversion of:

Answer 37

Succinyl CoA to Succinate

Question 38

Which enzyme is NOT found in the Glyoxylate Cycle? * Aconitase * Citrate synthase * Isocitrate lyase * Malate synthase * Isocitrate dehydrogenase

Answer 38

Isocitrate dehydrogenase

Question 39

Which citric acid cycle enzyme catalyzes the production of GTP?

Answer 39

Succinyl-CoA synthetase

Question 40

Which enzyme converts citrate to isocitrate?

Answer 40

Aconitase

Question 41

Which enzyme catalyzes the first oxidative decarboxylation reaction in the citric acid cycle and produces CO₂?

Answer 41

Isocitrate dehydrogenase

Question 42

Which compound inhibits the pyruvate dehydrogenase complex when present at high concentrations? * Pyruvate * NADH * Fructose 2,6-bisphosphate * AMP * HS-CoA

Answer 42

NADH

Question 43

Which citric acid cycle enzyme catalyzes the production of FADH₂?

Answer 43

Succinate dehydrogenase

Question 44

In the citric acid cycle, the first NADH is synthesized by the \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_reaction.

Answer 44

Isocitrate dehydrogenase

Question 45

T or F: The purpose of the citric acid cycle is to convert acetyl CoA to fatty acids.

Answer 45

False

Question 46

T or F: The rate of the citric acid cycle is reduced when the cell has high levels of NADH.

Answer 46

True

Question 47

In the citric acid cycle, GDP is phosphorylated to GTP during the conversion of ________________ to \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.

Answer 47

Succinyl CoA to Succinate

Question 48

Which citric acid cycle enzyme catalyzes the production of GTP or ATP?

Answer 48

Succinyl CoA Synthetase

Question 49

T or F: During the citric acid cycle FADH2 is produced by the enzymatic reaction catalyzed by fumarase.

Answer 49

False