Krebs Cycle Diagram: Intermediates, Carbon Counts, and Yield

Count One Acetyl Group Before Counting Glucose

A Krebs cycle diagram follows one turn that accepts a two-carbon acetyl group from acetyl-CoA. Four-carbon oxaloacetate combines with that group to form six-carbon citrate. The pathway later regenerates oxaloacetate, allowing another turn. It is also called the citric acid cycle or TCA cycle.

In the standard complete-oxidation model, one glucose supplies two acetyl-CoA, so the cycle turns twice. A yield labeled per turn is not a per-glucose yield. Pyruvate oxidation happens before entry and produces additional NADH and CO2 that should not be counted again inside the cycle.

Use the krebs cycle diagram generator to start a focused draft, then check it against the concepts below.

Carbon Counts Do Not Track Individual Carbon Atoms

Citrate and isocitrate contain six carbons. Conversion to alpha-ketoglutarate releases CO2 and leaves five, then conversion to succinyl-CoA releases another CO2 and leaves four. The remaining intermediates retain four carbons as oxaloacetate is regenerated.

These counts describe molecule size, not the identity of a particular carbon atom. In the first turn, the released CO2 carbons are not the newly entering acetyl carbons. A simple colored ring should not imply otherwise. An atom-tracing exercise needs a separate, carefully mapped model.

AI-generated mitochondrial vignette with an AcaDraw Krebs cycle diagram showing eight intermediates, carbon counts and per-turn products; qualitative, not to scale.

Carriers Are Products, Not All Direct ATP

The usual per-turn summary is three NADH, one FADH2 equivalent, one GTP or ATP, and two CO2. NADH and the succinate-oxidation electrons connect the cycle to electron transport; they are not themselves three or one molecules of directly produced ATP. The substrate-level phosphorylation step is separate from oxidative phosphorylation.

Most eukaryotic cycle enzymes operate in the mitochondrial matrix. Succinate dehydrogenase is associated with the inner membrane and passes electrons through FAD to ubiquinone, which is why FADH2 is best read as familiar yield shorthand here. Oxygen is not directly consumed by cycle reactions, though aerobic electron transport uses oxygen and supports carrier regeneration. See the cellular respiration diagram for the broader sequence.

Krebs Cycle Diagram Reference Key

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Common Questions

Are Krebs cycle and citric acid cycle the same?

Yes. The names Krebs cycle, citric acid cycle and TCA cycle refer to the same core pathway in this context.

Where does the Krebs cycle occur?

In eukaryotes most cycle enzymes are in the mitochondrial matrix. Succinate dehydrogenase is associated with the inner membrane; prokaryotes lack mitochondria.

What is produced per turn?

The standard summary is two CO2, three NADH, one FADH2 equivalent and one GTP or ATP per acetyl-CoA turn, with oxaloacetate regenerated.

How many turns occur per glucose?

Complete oxidation of one glucose typically supplies two acetyl-CoA, giving two cycle turns. State the counting basis explicitly.

Sources and Editorial Notes

• OpenStax Biology 2e: Oxidation of Pyruvate and the Citric Acid Cycle
• OpenStax Biology 2e: Oxidative Phosphorylation

Prepared by the AcaDraw product team. Source and illustration check: November 1, 2026. Original AI-generated illustration with AcaDraw labels and layout. This is a simplified teaching model; independent subject-expert review has not been completed. Check AI drafts against the cited references before sharing.