L25 Citric Acid Cycle (Krebs/TCA)

Question 1

The citric acid cycle harvests high-energy electrons from…

Answer 1

Carbon fuels

Question 2

Pyruvate is converted to acetyl CoA by…

Answer 2

Pyruvate dehydrogenase

Question 3

In step 2 citrate is rearranged to form the unstable molecule…

Answer 3

Isocitrate

Hydroxide is moved along 1 carbon

Question 4

Citrate is rearranged to isocitrate by…

Answer 4

Aconitase

Question 5

Isocitrate dehydrogenase converts…

Answer 5

Isocitrate to α-ketoglutarate

Question 6

During the conversion of isocitrate to α-ketoglutarate:

a) NAD+ → NADH
b) NADH → NAD+
c) FADH2 → FAD
d) GTP → GDP

Answer 6

a) NAD+ → NADH

Question 7

α-ketoglutarate is converted to…

Answer 7

Succinyl CoA

Question 8

Succinyl CoA is converted to succinate. This facilitates the conversion…

Answer 8

of GDP to GTP (oxidative phosphorylation)

Question 9

Succinate dehydrogenase converts…

Answer 9

Succinate to Fumarate

Question 10

Fumarase converts…

Answer 10

Fumarate to malate

Question 11

Malase dehydrogenase converts…

Answer 11

Malate to oxaloacetate

Question 12

The conversion of succinate to fumarate generates…

Answer 12

FADH2

Question 13

The conversion of Malate to oxaloacetate generates…

Answer 13

NADH

Question 14

In the final step of the citric acid cycle…

Answer 14

Citrate is regenerated from oxaloacetate and acetyl-CoA via citrate synthase

Question 15

The citric acid cycle is a:

a) amphibolic pathway
b) catabolic pathway
c) anabolic pathway

Answer 15

a) amphibolic pathway

It generates both catabolic and anabolic metabolites!

Question 16

Unlike glycolysis, the citric acid cycle is controlled by..

Answer 16

ADP (rather than AMP)

Question 17

Pyruvate dehydrogenase is a multienzyme complex witH:

a) 5 subunits
b) 3 subunits
c) 213 subunits
d) 132 subunits

Answer 17

d) 132 subunits

Question 18

Pyruvate dehydrogenase requires Vitamin B1 and which two other nutrients?

Answer 18

• Riboflavin (as FADH2)

* Niacin (as NAD)

Question 19

Beri-Beri is caused by…

Answer 19

B1 deficiency

Question 20

In Beri-Beri, pyruvate cannot be converted to…

Answer 20

Acetyl CoA

as there is insufficient B1

Question 21

Symptoms of Beri-Beri (3)…

Answer 21

• Loss of appetite
• Lassitude (from lack of ATP)
• Numbness (neurons not firing)

Question 22

Wernicke-Korsakoff encephalopathy is…

Answer 22

B1 deficiency in chronic alcoholics

Question 23

In addition to being converted to acetyl CoA to use in the citric acid cycle, pyruvate may also be converted to… (4)

Answer 23

• Lipids
• Amino acids
• Lactate
• Ethanol (in yeast and some bacteria)

Question 24

acetyl CoA is converted to lipids when…

Answer 24

ATP is plentiful

Question 25

acetyl CoA is converted to amino acids during…

Answer 25

High growth periods

Question 26

acetyl CoA is converted to lactate under…

Answer 26

Anaerobic conditions

Question 27

Ecstasy (MDMA) works by…

Answer 27

Inhibiting the pain from lactic acid buildup

Question 28

Key control points for the citric acid cycle occur at (3)…

Answer 28

1. Pyruvate → Acetyl CoA
2. Isocitrate → α-ketoglutarate
3. α-ketoglutarate → succinyl CoA

Question 29

High ADP and pyruvate will encourage the conversion of…

Answer 29

Pyruvate → Acetyl CoA

Question 30

High ATP and high NADH will inhibit citric acid cycle at:

a) Pyruvate → Acetyl CoA
b) Isocitrate → α-ketoglutarate
c) α-ketoglutarate → succinyl CoA
d) All of the above

Answer 30

d) All of the above