The citric acid cycle (also known as the Krebs cycle or TCA cycle) is the final common pathway for the complete oxidation of acetyl groups derived from carbohydrates, fats, and proteins to produce carbon dioxide. The cycle consists of 8 steps that occur in the mitochondrial matrix and produces reduced coenzymes (NADH and FADH2) that fuel the electron transport chain to produce ATP through oxidative phosphorylation. The cycle also provides precursors for various biosynthetic pathways. Overall, the oxidation of one acetyl group by the citric acid cycle generates 12 ATP, making it an important source of energy production in cells.

1. Citric acid cycle/Krebs
Cycle/TCA cycle
Presented By – Shubhrat Maheshwari

2. Introduction
CITRIC ACID CYCLE= TCA CYCLE =KREBS CYCLE
(TCA = Tricarboxylic acid cycle)
• In 1937, Sir Hans krebs proposed a complete cycle, and in 1953 got Nobel prize for it.
Definition:
• Acetyl CoA is completely oxidized to CO2 in a cycle of reactions with simultaneous production of energy is
termed as the citric acid cycle.
• Acetyl-CoA, is derived from pyruvate and other metabolites.
• All enzymes are in the mitochondrial matrix.

3. Functions of TCA cycle
• Final common oxidative pathway that oxidizes acetyl CoA to CO2.
• The source of reduced coenzymes that provide the substrate for the respiratory chain.
• The link between catabolic and anabolic pathways (amphibolic role).
• Provides precursors for synthesis of amino acids and nucleotides.
• Components of the cycle have a direct or indirect controlling effects on key enzymes of the pathways.
The citric acid cycle is final common oxidative pathway
CO2

4. Citric Acid Cycle
• After Glycolysis, Pyruvate inter in mitochondria
• Pyruvate decarboxylated and converted in Acetyl CoA. This step catalyzed by pyruvate dehydrogenase
enzyme. This reaction is a link between glycolysis and TCA (Tricarboxlic acid) cycle.
Fig :Conversion of pyruvate to acetyl-CoA

6. (Where: GTP= Guanine triphosphate;
GDP= Guanine Diphosphate;
FAD = Flavin adenine dinucleotide,
FADH2= Flavin adenine dinucleotide dihydride;
NAD= Nicotinamide adenine dinucleotide;
NADH= Nicotinamide adenine dinucleotide hydride)

7. Energetics
• Energetics of TCA Cycle=
• 3ATP (1 NADH, Step 3) + 3ATP (1 NADH, Step 4) + 1ATP (1 GTP, Step 5) + 2ATP (1 FADH2, Step 6) +
3ATP (1 NADH, Step 7) = 12 ATP generated.
• Overall TCA cycle produce 2CO2 molecule and generated 12 ATP.
• Hence, 2 Acetyl Co A produce total energy= 12 x 2= 24
• Energetic in complete oxidation of a glucose molecule:

8. Significance of TCA Cycle

9. Trick to learn krebs cycle
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Smart Staff For Main Office
Cricket – citrate
Coach – cis- Aconitate
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Office- oxaloacetate