What is the yield of one turn of the citric acid cycle?

Per acetyl-CoA (one turn): 3 NADH, 1 FADH2, 1 GTP, and 2 CO2. Since glycolysis produces 2 pyruvate per glucose, which pyruvate dehydrogenase converts into 2 acetyl-CoA, the cycle runs twice per glucose, doubling everything to 6 NADH, 2 FADH2, 2 GTP, and 4 CO2.

What are the three regulated steps of the citric acid cycle?

Citrate synthase (step 1), isocitrate dehydrogenase (step 3, the rate-limiting step), and alpha-ketoglutarate dehydrogenase (step 4). All three are irreversible under cellular conditions and inhibited by high ATP/NADH, activated by ADP and calcium.

Is the GTP made in the cycle the same as ATP?

Functionally yes for energy accounting purposes, nucleoside diphosphate kinase readily converts GTP to ATP (and vice versa), so most textbooks and this site's ATP yield calculator count the cycle's GTP as equivalent to ATP when tallying total energy yield.

Citric Acid Cycle Explorer: 8 Steps, Free

Q: Why is succinate dehydrogenase different from the other 7 enzymes?

It's the only citric acid cycle enzyme embedded directly in the inner mitochondrial membrane rather than free in the mitochondrial matrix, because it doubles as Complex II of the electron transport chain. That's why its FADH2 electrons feed into the ETC without a separate shuttle step, unlike the NADH produced by the other three oxidative steps.

Step

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NADH

FADH₂

GTP

CO₂

One turn of the cycle, and why it runs twice per glucose

One acetyl-CoA entering the cycle (one "turn") yields 3 NADH, 1 FADH₂, 1 GTP, and 2 CO₂, while regenerating the oxaloacetate the cycle started with so it can accept another acetyl-CoA. Glycolysis produces 2 pyruvate per glucose, and pyruvate dehydrogenase converts each pyruvate into one acetyl-CoA, so the cycle runs twice per original glucose, doubling everything to 6 NADH, 2 FADH₂, 2 GTP, and 4 CO₂. Those are exactly the citric acid cycle numbers used in the ATP yield calculator.

This is specifically the aerobic continuation of glucose breakdown, the cycle only runs when oxygen is available to keep the electron transport chain (and therefore NAD⁺ regeneration) going. Without oxygen, pyruvate never reaches this cycle at all; it goes to fermentation instead, purely to regenerate the NAD⁺ glycolysis needs. See what happens to pyruvate and NADH without oxygen for that side of the fork.

Model note: standard textbook citric acid cycle (Lehninger). GTP is counted as ATP-equivalent (nucleoside diphosphate kinase interconverts them freely), matching the convention used across this site.

Worked example: the running tally, step by step

Tracking cumulative NADH, FADH₂, GTP, and CO₂ after each step, exactly what the tally bar above computes as you click through:

Step 1 Citrate synthase (no change) Step 2 Aconitase (no change) Step 3 Isocitrate dehydrogenase NADH +1, CO2 +1 → cumulative NADH: 1, CO2: 1 Step 4 α-Ketoglutarate dehydrogenase NADH +1, CO2 +1 → cumulative NADH: 2, CO2: 2 Step 5 Succinyl-CoA synthetase GTP +1 → cumulative GTP: 1 Step 6 Succinate dehydrogenase FADH2 +1 → cumulative FADH2: 1 Step 7 Fumarase (no change) Step 8 Malate dehydrogenase NADH +1 → cumulative NADH: 3 Final (one turn): NADH = 3, FADH2 = 1, GTP = 1, CO2 = 2

Both carbons lost as CO₂ (steps 3 and 4) come from the oxaloacetate/citrate carbon skeleton, not directly from the acetyl-CoA that entered this turn, but the cycle still nets zero carbons gained, since oxaloacetate is fully regenerated by step 8.

Printable citric acid cycle chart

All eight steps on one page with the enzyme for each, what it yields, and which three are regulated. Pairs with the glycolysis chart, since together they cover almost everything before the electron transport chain.

Download the chart, or the print-friendly white version. Free for a study guide or class handout, no attribution needed. See all the printable charts.

FAQ

What is the yield of one turn of the cycle?
Per acetyl-CoA: 3 NADH, 1 FADH₂, 1 GTP, 2 CO₂. Twice per glucose (2 acetyl-CoA from 2 pyruvate): 6 NADH, 2 FADH₂, 2 GTP, 4 CO₂.

What are the three regulated steps?
Citrate synthase (step 1), isocitrate dehydrogenase (step 3, rate-limiting), and α-ketoglutarate dehydrogenase (step 4), all irreversible under cellular conditions, inhibited by high ATP/NADH, activated by ADP/calcium.

Why is succinate dehydrogenase different from the rest?
It's the only cycle enzyme embedded in the inner mitochondrial membrane, since it doubles as Complex II of the electron transport chain. Its FADH₂ electrons feed the ETC directly, unlike the NADH from the other three oxidative steps.

Is the GTP the same as ATP?
Functionally yes for energy accounting, nucleoside diphosphate kinase readily interconverts GTP and ATP, so most textbooks (and this site's ATP yield calculator) count them as equivalent.

Practice problems

1. A cell processes 10 acetyl-CoA through the citric acid cycle (10 turns). What's the total NADH, FADH₂, GTP, and CO₂?

Show answer

Per turn: 3 NADH, 1 FADH2, 1 GTP, 2 CO2, scales linearly since each acetyl-CoA is processed independently. 10 × 3 NADH = 30 NADH 10 × 1 FADH2 = 10 FADH2 10 × 1 GTP = 10 GTP 10 × 2 CO2 = 20 CO2

2. Using the modern P/O ratios from the ATP yield calculator (2.5 ATP/NADH, 1.5 ATP/FADH2), how much total ATP does one full turn of the citric acid cycle contribute, counting both oxidative phosphorylation and the substrate-level GTP?

Show answer

Oxidative phosphorylation: 3 NADH × 2.5 + 1 FADH2 × 1.5 = 7.5 + 1.5 = 9 ATP Substrate-level: 1 GTP = 1 ATP-equivalent Total per turn = 9 + 1 = 10 ATP Per glucose (×2 turns) = 20 ATP, which is exactly the citric acid cycle's share of the 32 ATP total shown by default in the ATP yield calculator.

Just the glycolysis number? How many ATP are produced in glycolysis? Net 2 ATP per glucose, with the exact steps that spend and make it.