gen-define-the-citric-acid-tca-cycle-and-give-one-short-worked-e-1f6e

Define the citric acid (TCA) cycle and give one short worked example.

# Citric Acid (TCA) Cycle ## Definition The **citric acid cycle** (also called the TCA cycle or Krebs cycle) is a series of eight enzyme-catalyzed chemical reactions that occurs in the mitochondrial matrix. It is the central metabolic pathway that: - Oxidizes acetyl-CoA (derived from carbohydrates, fats, and proteins) to CO₂ - Generates high-energy electron carriers (NADH and FADH₂) for the electron transport chain - Produces GTP/ATP directly - Provides biosynthetic precursors for amino acids and other molecules **Net equation per acetyl-CoA:** ``` Acetyl-CoA + 3NAD⁺ + FAD + GDP + Pᵢ + 2H₂O → 2CO₂ + 3NADH + FADH₂ + GTP + 2H⁺ + CoA-SH ``` --- ## Worked Example **Question:** How much ATP can be generated from one molecule of acetyl-CoA going through the TCA cycle and oxidative phosphorylation? **Solution:** From **one turn** of the TCA cycle: - 3 NADH × 2.5 ATP each = **7.5 ATP** - 1 FADH₂ × 1.5 ATP = **1.5 ATP** - 1 GTP = **1 ATP** **Total = ~10 ATP per acetyl-CoA** (Note: ATP yields vary slightly depending on shuttle systems and efficiency)