How Many ATPs Produced in Krebs Cycle

Introduction

The tricarboxylic acid (TCA) cycle, also known as the Krebs or citric acid cycle, is the primary source of energy for cells and an essential phase in aerobic respiration.The procedure transforms the chemical energy of acetyl coenzyme A (acetyl CoA) into the reducing force of nicotinamide adenine dinucleotide (NADH). The TCA cycle is a part of the larger glucose metabolism, which entails the oxidation of glucose to produce pyruvate, which is then subjected to further oxidation before entering the TCA cycle as acetyl-CoA. The intermediates from the first part of the cycle are also the starting point for pathways that lead to significant compounds such as fatty acids, amino acids, or porphyrins. If any of these intermediates are present, the cycle's integrity is jeopardised and it can no longer function. Vital energy generation can only resume if anaplerotic (refilling) mechanisms can replace the diverted intermediate or a following intermediate that leads to oxaloacetate.

Krebs Cycle Intermediates

1. Citrate

2. Isocitrate

3. Oxoglutarate

4. Succinyl-CoA

5. Succinate

6. Fumarate

7. Malate

8. Oxaloacetate (oxaloacetic acid)

Krebs Cycle Steps

1. The TCA cycle is started by the enzyme-mediated aldol addition reaction of acetyl CoA to oxaloacetate, which yields citrate.

2. A dehydration-hydration sequence is used to isomerize the citrate, producing (2R,3S)-isocitrate.

3. Further enzymatic oxidation and decarboxylation result in 2-ketoglutarate.

4. 2-Ketoglutarate is converted into succinyl-CoA through additional enzymatic decarboxylation and oxidation.

5. Guanosine diphosphate (GDP) undergoes simultaneous hydrolysis to succinate and phosphorylation to guanosine triphosphate (GTP).

6. Succinate dehydrogenase, an enzyme dependent on the flavin adenine dinucleotide, generates fumarate (FAD).

7. After stereospecific hydration, fumarase converts fumarate to L-malate.

8. Malate dehydrogenase catalyses the final step of the NAD-coupled oxidation of L-malate to oxaloacetate, which completes the cycle.

Key Enzymes of Krebs Cycle

• Malic dehydrogenase

• α-Ketoglutarate dehydrogenase

• Citrate synthase

• Fumarase

• Aconitase

Krebs Cycle Products

One "cycle" of the TCA cycle tends to produce seven products:

• GTP

• 3 NADH

• FADH2, which, when exposed to coenzyme Q, transforms into UQH2 (ubiquinone)

• 2 CO2 (carbon dioxide)

Applications of Krebs Cycle

• Lipid Metabolism

• Amino Acid Metabolism

• Protein Metabolism (Turnover)

• Glucose Metabolism

• Energy Expenditure

• Metabolomics

Conclusion

• 1 FADH2 is equivalent to 2 ATP

• 1 NADH2 is equivalent to 3 ATP

• So to sum it all up, a total of 12 ATPs are formed in a single turn of the Krebbs cycle, of which one is direct and 11 are indirect.

• Similarly, 2 Krebbs cycles occur for 1 glucose molecule, resulting in the production of 24 ATPs in total.