TCA Cycle and Pyruvate Dehydrogenase: Reactions, Regulation, and Clinical Impairments

What is the overall reaction of the pyruvate dehydrogenase complex?

The conversion of pyruvate to acetyl-CoA, which occurs in the mitochondria.

What is the significance of the TCA cycle?

It accounts for over 70% of ATP generated from fuel oxidation and provides precursors for biomolecules.

What are the main products of one cycle of the TCA cycle?

3 NADH, 1 FADH2, 1 GTP (converted to ATP), and 2 CO2.

What is substrate-level phosphorylation?

The direct generation of ATP from GTP in the TCA cycle.

Who is the TCA cycle named after?

Sir Hans Krebs, who formulated its reactions.

What is the first compound formed in the TCA cycle?

Citrate, derived from acetyl-CoA and oxaloacetate.

What is Acetyl-CoA?

An acetyl group attached to coenzyme A, serving as the fuel for the TCA cycle.

Where does the TCA cycle occur in the cell?

In the mitochondria of all cells except red blood cells.

What regulates the TCA cycle?

Supply and demand of energy; it slows down during high-energy states and accelerates during low-energy states.

What vitamins and minerals are required for the TCA cycle?

Vitamins such as B5 (pantothenic acid) and minerals like magnesium.

What is the role of pyruvate dehydrogenase (PDH)?

It catalyzes the conversion of pyruvate to acetyl-CoA, linking glycolysis to the TCA cycle.

What happens to acetyl-CoA in the TCA cycle?

It is oxidized to generate CO2 and high-energy molecules (NADH, FADH2, GTP).

What are the byproducts of the TCA cycle?

2 CO2 and high-energy molecules (3 NADH, 1 FADH2, 1 GTP).

How many ATP are generated from one cycle of the TCA cycle?

A total of 12 ATP can be generated from the high-energy molecules produced.

What is the common source of acetyl-CoA?

Breakdown of ketone bodies, fatty acids, and some amino acids.

What is the function of the TCA cycle in gluconeogenesis?

It provides intermediates necessary for the synthesis of glucose in the liver.

What are anaplerotic reactions in the TCA cycle?

Reactions that replenish TCA cycle intermediates.

What is the role of NADH and FADH2 in cellular respiration?

They serve as electron carriers in the electron transport chain to produce ATP.

What is the significance of the TCA cycle in metabolism?

It is the final step for major biochemical pathways of fuel oxidation.

What happens to pyruvate during aerobic glycolysis?

It is converted to acetyl-CoA by pyruvate dehydrogenase.

What is the effect of arsenic poisoning on the TCA cycle?

It impairs the function of pyruvate dehydrogenase and other enzymes in the cycle.

How does beriberi affect the TCA cycle?

It impairs the function of enzymes that require thiamine (vitamin B1) for the TCA cycle.

What is the total carbon count for acetyl-CoA and its derivatives in the TCA cycle?

Acetyl-CoA (2C) combines with oxaloacetate (4C) to form citrate (6C).

What is the overall net energy gain in terms of ATP for each cycle of the Krebs cycle?

The net gain is typically considered to be 10 ATP.

What is the role of pyruvate dehydrogenase in energy metabolism?

It regulates the flow of pyruvate into the TCA cycle.

Where is pyruvate dehydrogenase located?

In the mitochondrial matrix.

What reaction does pyruvate dehydrogenase catalyze?

The conversion of pyruvate to acetyl-CoA.

What are the products of the conversion of pyruvate to acetyl-CoA?

Acetyl-CoA and CO2.

What is TPP and its role in pyruvate dehydrogenase?

Thiamine pyrophosphate, a prosthetic group derived from vitamin B1, is permanently bound to the enzyme.

What is the role of lipoic acid in pyruvate dehydrogenase?

It is a covalently bound prosthetic group.

What is Coenzyme A derived from?

Pantothenic acid (vitamin B5).

What is the significance of FAD in pyruvate dehydrogenase?

FAD is a prosthetic group derived from riboflavin (Vitamin B2).

What is the role of NAD in pyruvate dehydrogenase?

NAD is a transiently bound cofactor derived from niacin (Vitamin B3).

What inhibits the activity of pyruvate dehydrogenase?

High energy state indicated by high levels of NADH, FADH2, and ATP.

What is the effect of arsenic poisoning on pyruvate dehydrogenase?

Arsenic binds to lipoic acid, blocking PDH and α-ketoglutarate dehydrogenase activity.

What is beriberi and its relation to thiamine deficiency?

Beriberi is the classical presentation of thiamine deficiency, leading to impaired PDH activity.

Why is thiamine deficiency particularly damaging to the heart and brain?

These organs have large energy requirements.

What are the three irreversible steps of the TCA cycle?

1. Citrate Synthase, 2. Isocitrate Dehydrogenase, 3. α-Ketoglutarate Dehydrogenase.

What inhibits citrate synthase in the TCA cycle?

ATP and NADH (high energy state).

What inhibits isocitrate dehydrogenase?

ATP and NADH (high energy state).

What inhibits α-ketoglutarate dehydrogenase?

ATP, NADH (high energy state), and arsenic.

What are anaplerotic reactions?

Reactions that add intermediates to the TCA cycle from various dietary precursors, mainly amino acids.

How do TCA cycle intermediates contribute to anabolic reactions?

They are used to synthesize other vital biomolecules like fatty acids.

What is the net ATP yield from one glucose molecule during aerobic respiration?

38 ATP.

What is the role of oxaloacetic acid in gluconeogenesis?

It can be converted to glucose during starvation.

What is the significance of the TCA cycle in gluconeogenesis?

It serves as a major gateway for gluconeogenesis.