Kreb's Cycle

Question 1

What is the significance of the Kreb’s Cycle?

Answer 1

1. It is the common pathway in the oxidation of carbohydrates, lipids and proteins.
2. Main function is the oxidation of Acetyl CoA to 2CO2.
3. Produces FADH2 and NADH (reduced equivalents)
4. It is an amphbolic pathway.
5. Provides intermediates for protein and nucleotide synthesis and keto-acids for non-essential amino acids.

Question 2

Where does the Kreb’s Cycle take place?

Answer 2

Mitchondrial Matrix

Question 3

True or False: The Kreb’s Cycle operate only under aerobic conditions.

Answer 3

True

Question 4

How is the Kreb’s Cycle a catabolic pathway?

Answer 4

1. It oxidises Acetyl CoA to 2CO2
2. It conserves energy in the form of reduced co-enzymes.

Question 5

How is TCA cycle an anabolic pathway?

Answer 5

The TCA cycle provides intermediates for biosysthesis such as:
1. Cholestrol synthesis: Acetyl CoA to Citrate
2. Amino Acid synthesis: Oxaloacetate and ketoglutarate
3. Gluconeogenesis: Oxaloacetate
4. Heme Synthesis: Succinyl CoA

Question 6

What are anaplerotic reactions?

Answer 6

Reactions that replenish TCA cycle intermediates.

Question 7

What are some example of anaplerotic reactions?

Answer 7

1. Oxaloacetate: Carboxylation of pyruvate in the presence of pyruvate carboxylase using 1 ATP; Transamination and Deamination
2. Succinyl CoA: Breakdown of Methionine, Valine and Isoleucine; Oxidation of odd fatty acids
3. Alpha ketoglutarate: Transamination and deamination

Question 8

What are the rate regulating steps of the TCA cycle?

Answer 8

The rate regulating steps of the TCA cycle are:
1. Acetyl CoA to Citrate (Citrate synthase)
2. Isocitrate to alpha-ketoglutarate (Isocitrate dehydrogenase)
3. Alpha ketoglutarate to Succinyl CoA (Alpha ketoglutarate dehydrogenase)

Question 9

What inhibits Citrate Synthase?

Answer 9

1. NADH
2. ATP
3. Succinyl CoA

Question 10

How is the formation of alpha ketoglutarate from isocitrate regulated?

Answer 10

The enzyme isocitrate synthase is:
Inhibited by- ATP, NADH
Stimulated by- Ca2+, ADP

Question 11

What inhibits alpha ketoglutarate dehydrogenase?

Answer 11

1. NADH
2. Succinyl CoA

Question 12

Why is the availability of ADP in the TCA cycle very important?

Answer 12

1. Inavailability of ADP will prevent NADH and FADH2 from oxidising and they will accumulate, inhibiting main enzymes.
2. Won’t generate NAD+ and FAD+, so the TCA cycle won’t proceed.