Overview of Citric Acid Cycle and Pyruvate Oxidation

These flashcards cover key concepts related to the citric acid cycle, pyruvate oxidation, and regulation of metabolic pathways.

What is the main function of the pyruvate dehydrogenase (PDH) complex?

The PDH complex oxidizes pyruvate to acetyl-CoA, producing CO2 and NADH.

What are the end products of the PDH net reaction?

Acetyl-CoA, CO2, and NADH.

Which vitamin B1 is a cofactor for PDH and plays a role in the formation of acetyl-CoA?

Thiamine (Vitamin B1) acts as a cofactor for PDH.

What is the role of Acetyl-CoA in the citric acid cycle?

Acetyl-CoA enters the citric acid cycle to be oxidized, ultimately producing CO2, NADH, and FADH2.

What are the main regulatory factors of PDH?

PDH is inhibited by ATP, acetyl-CoA, and NADH, and activated by AMP, CoA, and NAD+.

What is the role of coenzyme A (CoA) in metabolism?

CoA carries acyl groups in thioester bonds, facilitating the entry of these groups into metabolic pathways.

Which intermediates are produced in the citric acid cycle?

Intermediates include citrate, isocitrate, alpha-ketoglutarate, succinyl-CoA, succinate, fumarate, and malate.

What is the importance of the citric acid cycle in cellular respiration?

The citric acid cycle is essential for the complete oxidation of organic material to produce ATP through oxidative phosphorylation.

How does the glyoxylate cycle differ from the citric acid cycle?

The glyoxylate cycle allows plants and microorganisms to convert Acetyl-CoA to glucose, which mammals cannot do.

What are the two main anaplerotic reactions in the citric acid cycle?

Carboxylation of pyruvate to oxaloacetate and conversion of phosphoenolpyruvate (PEP) to oxaloacetate.

What is the citric acid cycle?

The citric acid cycle, also known as the Krebs cycle, is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA.

What are the main products of the citric acid cycle?

The main products of the citric acid cycle are carbon dioxide (CO2), NADH, FADH2, and ATP.

How many times does the citric acid cycle turn per glucose molecule?

The citric acid cycle turns twice for each glucose molecule, as one glucose is broken down into two molecules of pyruvate.

What molecule begins the citric acid cycle?

The citric acid cycle begins with the condensation of Acetyl-CoA and oxaloacetate to form citrate.

Why is the citric acid cycle considered a central metabolic pathway?

The citric acid cycle is considered a central metabolic pathway because it integrates carbohydrate, fat, and protein metabolism, playing a key role in energy production.

What is the enzyme that catalyzes the conversion of Acetyl-CoA and oxaloacetate to citrate?

The enzyme is citrate synthase.

Which enzyme is responsible for the oxidative decarboxylation of isocitrate to alpha-ketoglutarate?

The enzyme is isocitrate dehydrogenase.

What is the role of alpha-ketoglutarate dehydrogenase in the citric acid cycle?

This enzyme catalyzes the conversion of alpha-ketoglutarate to succinyl-CoA, producing NADH and CO2.

How is the activity of citrate synthase regulated?

Citrate synthase is regulated by the availability of substrates (Acetyl-CoA and oxaloacetate) and inhibited by its products (citrate and succinyl-CoA).

What role do NADH and ATP play as regulatory molecules in the citric acid cycle?

NADH and ATP act as inhibitors of key enzymes like isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase, thereby regulating the cycle based on the energy needs of the cell.

What is the first step of the citric acid cycle?

The first step involves the condensation of Acetyl-CoA and oxaloacetate to form citrate, catalyzed by the enzyme citrate synthase.

What is the second step of the citric acid cycle?

In the second step, citrate is converted to isocitrate through the enzyme aconitase.

What is the third step of the citric acid cycle?

The third step involves the oxidative decarboxylation of isocitrate to alpha-ketoglutarate, catalyzed by isocitrate dehydrogenase.

What is the fourth step of the citric acid cycle?

In the fourth step, alpha-ketoglutarate is converted to succinyl-CoA by alpha-ketoglutarate dehydrogenase.

What is the fifth step of the citric acid cycle?

The fifth step involves the conversion of succinyl-CoA to succinate, which produces ATP or GTP, catalyzed by succinyl-CoA synthetase.

What is the sixth step of the citric acid cycle?

In the sixth step, succinate is oxidized to fumarate by the enzyme succinate dehydrogenase, producing FADH2.

What is the seventh step of the citric acid cycle?

The seventh step involves the hydration of fumarate to malate, catalyzed by fumarase.

What is the eighth step of the citric acid cycle?

In the eighth step, malate is oxidized to oxaloacetate by malate dehydrogenase, generating NADH.

What is the net reaction of the citric acid cycle per acetyl-CoA molecule?

3 NAD+ + FAD + GDP + P_i + Acetyl-CoA -> 3 NADH + FADH2 + GTP + 2 CO2 + CoA.

What conversion occurs from pyruvate to Acetyl-CoA?

The conversion from pyruvate to acetyl-CoA occurs through oxidative decarboxylation, catalyzed by the pyruvate dehydrogenase complex, producing CO2 and NADH.