Citric acid cycle

Citric Acid Cycle

A key metabolic pathway also known as the Krebs cycle, occurring in the mitochondrial matrix of cells.

Purpose

The final common pathway for the oxidation of fuel molecules, releasing energy stored in their chemical bonds.

Location

Occurs in the mitochondrial matrix in eukaryotes and the cytoplasm in prokaryotes.

Acetyl-CoA

A 2-carbon molecule that enters the citric acid cycle.

Enzyme-catalyzed reactions

The cycle consists of a series of 8 reactions facilitated by enzymes.

Products per turn

The cycle produces 2 CO2 molecules, 1 ATP (or GTP), 3 NADH, and 1 FADH2.

Citrate

A 6-carbon molecule formed when Acetyl-CoA combines with oxaloacetate.

Oxaloacetate

A 4-carbon molecule that is regenerated at the end of the cycle, allowing it to continue.

Energy production

The cycle directly produces 1 ATP (or GTP) and generates reduced coenzymes (NADH and FADH2) for ATP production.

Cycle turns

For each glucose molecule, the citric acid cycle turns twice.

Regulation

The cycle is tightly controlled by allosteric regulation and product inhibition.

Key regulatory enzymes

Citrate synthase, isocitrate dehydrogenase, and α-ketoglutarate dehydrogenase are crucial for regulation.

Anaplerotic reactions

Reactions that replenish intermediates of the citric acid cycle.

Amphibolic nature

The cycle functions in both catabolism (breaking down molecules) and anabolism (building up molecules).

Connection to other pathways

The cycle links to glycolysis, fatty acid oxidation, and amino acid metabolism, providing precursors for biosynthesis.

Aerobic respiration

The citric acid cycle is crucial for aerobic respiration, playing a central role in energy production and metabolic integration in cells.

What is the purpose of the citric acid cycle

It's the final common pathway for the oxidation of fuel molecules (carbohydrates, fats, and proteins), releasing energy stored in their chemical bonds.

Give an overview of the citric acid cycle

• Acetyl-CoA (2-carbon molecule) enters the cycle

• Goes through a series of 8 enzyme-catalyzed reactions

• Produces 2 CO2 molecules, 1 ATP (or GTP), 3 NADH, and 1 FADH2 per turn

What are the key steps in the citric acid cycle

• Acetyl-CoA combines with oxaloacetate to form citrate (6-carbon molecule)

• Through subsequent steps, citrate is oxidized back to oxaloacetate

• CO2 is released at two points in the cycle

Describe the energy production in the citric acid cycle

• Directly produces 1 ATP (or GTP) per cycle

• Generates reduced coenzymes (3NADH and 1FADH2) that feed into the electron transport chain for ATP production

Describe the cyclic nature of the kreb/citric acid cycle

• Oxaloacetate is regenerated at the end, allowing the cycle to continue

• For each glucose molecule, the cycle turns twice

How is the kreb cycle regulated

• Tightly controlled by allosteric regulation and product inhibition

• Key regulatory enzymes: citrate synthase, isocitrate dehydrogenase, and α-ketoglutarate dehydrogenase

What is an Anaplerotic reaction

A metabolic pathway that replenishes intermediates in the citric acid cycle (Krebs cycle).

Help maintain the cycle's function by providing necessary substrates that may be depleted during other metabolic processes.

Common anaplerotic reactions include the conversion of pyruvate to oxaloacetate and the carboxylation of phosphoenolpyruvate to oxaloacetate.

Describe the Amphibolic nature of the Kreb cycle

Functions in both catabolism (breaking down molecules) and anabolism (building up molecules)

Describe how the kreb cycle links with other pathways

• Links to glycolysis, fatty acid oxidation, and amino acid metabolism

• Provides precursors for biosynthesis of various molecules