Citric Acid Cycle Summary

The Citric Acid Cycle Overview

• Pathway fully oxidizes two carbon atoms from glucose via acetyl CoA.

• Involves the oxidation of carboxylic acids; carbon dioxide is a byproduct.

Discovery and Mechanism

• Sequence of reactions identified as a cycle by Hans Krebs, relating to pyruvate processing.

• Pyruvate converts to citrate via the citric acid cycle, starting with acetyl CoA and releasing CO₂.

Cycle Characteristics

• Known as the Citric Acid Cycle, Tricarboxylic Acid (TCA) Cycle, or Krebs Cycle.

• Each cycle generates: 3 NADH, 1 FADH₂, and ATP or GTP via substrate-level phosphorylation.

• The cycle turns twice per glucose molecule due to glycolysis producing two pyruvate.

Regulation

• Controlled by feedback inhibition correlated with ATP and NADH levels.

• Inhibitors: ATP at allosteric sites, NADH through competitive inhibition.

Outputs

• Each cycle results in 2 CO₂ released, completing carbon oxidation from glucose.

• Total energy yield from glucose oxidation: 10 NADH, 2 FADH₂, and 4 ATP produced in glycolysis and the citric acid cycle.

• CO₂ produced is exhaled by organisms.

Energy Transfer

• During glucose oxidation, chemical energy in the form of ATP, NADH, and FADH₂ is harnessed through redox reactions.