Chapter 17: The Citric Acid Cycle

Question 1

Describe how glycolysis leads into the citric acid cycle?

What is the balanced equation?

Answer 1

The pyruvate dehydrogenase complex converts pyruvate into acetyl CoA. Acetyl CoA is the fuel for the citric acid cycle.

Equation:
Pyruvate + CoA + NAD+ —> acetyl CoA + NADH + CO2+ H+

Question 2

In what situations would glycolysis not lead into the citric acid cycle?

Answer 2

Answer:

Question 3

Where in the cell does the citric acid cycle take place?

Answer 3

Answer:

Question 4

What factors regulate the citric acid cycle?

Answer 4

1) Substrate availability can accelerate or slow down the citric acid cycle.
2) Allosteric regulation of:
- citrate synthase
- isocitrate dehydrogenase
- alpha-keptglutarate dehydrogenase complex

Question 5

Which components and by-products of the citric acid cycle are used by other processes? Name the molecule used and the process it is used in.

Answer 5

Answer:

Question 6

Why can’t fatty acids (usually) be used for the production of glucose?

Answer 6

The conversion of pyruvate into acetyl CoA is an irreversible reaction.
Most fatty acids when entering respiration are converted to acetyl CoA for use as fuel for the citric acid cycle.
Since acetyl CoA cannot be converted to pyruvate, it cannot be used to initiate gluconeogenesis and create glucose.

Question 7

How is the conversion of pyruvate to acetyl CoA regulated?

Answer 7

The pyruvate dehydrogenase complex is allosterically regulated.
Allosteric activators: CoA, NAD+, Pyruvate, AMP, Ca2+
Allosteric inhibitors: acetyl CoA, NADH, ATP, Fatty acids

Question 8

How many carbons enter the citric acid cycle with acetyl CoA and where do they exit the cycle?

Answer 8

2 carbons enter with acetyl CoA
They both exit as CO2.
1st from conversion of isocitrate to alpha-ketoglutarate
2nd from conversion of alpha-ketoglutarate to succinyl CoA

Question 9

What are the allosteric activators and inhibitors of citrate synthase?

Answer 9

Activators: ADP
Inhibitors: NADH, ATP, citrate, succinyl CoA

Question 10

What are the allosteric activators and inhibitors of isocitrate dehydrogenase?

Answer 10

Activators: ADP, Ca2+
Inhibitors: NADH, ATP

Question 11

What are the allosteric activators and inhibitors of the alpha-ketoglutarate dehydrogenase complex?

Answer 11

Activators: Ca2+
Inhibitors: NADH, Succinyl CoA