How many ATP does the Krebs cycle produce?

Each revolution of the Krebs cycle directly produces 1 GTP, which is functionally equivalent to 1 ATP through substrate-level phosphorylation. In addition, the 3 NADH and 1 FADH2 generated per turn feed into the electron transport chain, yielding roughly 9 more ATP (about 2.5 per NADH and 1.5 per FADH2). Because glucose generates 2 acetyl-CoA molecules, the cycle runs twice, contributing around 20 ATP per glucose in total.

What are the 8 steps of the Krebs cycle?

The eight steps are: (1) citrate formation from acetyl-CoA and oxaloacetate, (2) isomerization of citrate to isocitrate, (3) oxidative decarboxylation to alpha-ketoglutarate with NADH and CO2 release, (4) oxidative decarboxylation to succinyl-CoA with NADH and CO2 release, (5) GTP generation through substrate-level phosphorylation, (6) oxidation of succinate to fumarate producing FADH2, (7) hydration of fumarate to malate, and (8) oxidation of malate back to oxaloacetate producing NADH.

Why is the Krebs cycle also called the citric acid cycle?

The pathway takes its common name from citrate, the first compound formed when acetyl-CoA condenses with oxaloacetate in step 1. Citrate is the ionized form of citric acid, so the route became known as the citric acid cycle. It is also called the tricarboxylic acid (TCA) cycle because citrate carries three carboxyl groups. Hans Krebs described the complete cycle in 1937 and was awarded the Nobel Prize in Physiology or Medicine in 1953.

Where does the Krebs cycle take place?

The Krebs cycle runs inside the mitochondrial matrix of eukaryotic cells. Pyruvate generated by glycolysis in the cytoplasm is shuttled into the mitochondrion, where the pyruvate dehydrogenase complex converts it to acetyl-CoA before it enters the cycle. The NADH and FADH2 produced in the matrix then hand off electrons to the electron transport chain proteins embedded in the inner mitochondrial membrane.

Can I create a blank Krebs cycle diagram for quizzes?

Absolutely. The Figviz generator can produce blank Krebs cycle templates well suited for quizzes and take-home worksheets. Just request a blank layout with numbered slots for intermediate names, enzyme labels, and product checkboxes. Students fill in each field from memory, making it a straightforward way to assess understanding of the full pathway.

For Students

Krebs Cycle Diagram Krebs Cycle

Tell our AI what kind of Krebs cycle diagram you need and it will build one for you in moments. Ideal for biochemistry coursework, exam prep, and scientific presentations.

✓All 8 Enzymatic Steps✓Energy Carrier Tracking✓Enzyme & Substrate Labels✓Publication-Ready Quality

Krebs Cycle Diagram Examples

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Complete Labeled Krebs Cycle

A thorough Krebs cycle (citric acid cycle) map covering all 8 enzymatic steps, pathway intermediates, and energy carriers with clear annotations throughout.

krebs-cyclecitric-acid-cyclebiochemistry

Simplified Krebs Cycle Overview

A beginner-friendly overview of the Krebs cycle that spotlights key inputs such as acetyl-CoA and NAD+ alongside outputs including NADH, FADH2, ATP, and CO2.

simplifiedoverviewmetabolism

Krebs Cycle with Enzymes

An enzyme-centered Krebs cycle layout that distinguishes the 8 catalytic enzymes at each step and calls out the key regulatory ones.

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Energy Carrier Focus Diagram

An energy-output view of the Krebs cycle that pinpoints exactly where NADH, FADH2, and ATP are generated at each reaction step.

energyNADHFADH2

Krebs Cycle in Mitochondria Context

The Krebs cycle placed inside a mitochondrion cross-section, illustrating how it feeds electron carriers to the electron transport chain and connects with broader cellular respiration.

mitochondriacellular-respirationETC

Blank Krebs Cycle for Quiz

A printable Krebs cycle worksheet with numbered empty boxes for students to complete by filling in substrates, enzymes, and reaction products.

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Prompt templates you can copy

Start with one of these examples, then adapt the subject, labels, data, or layout for your own use.

Complete Labeled Krebs Cycle

A thorough Krebs cycle (citric acid cycle) map covering all 8 enzymatic steps, pathway intermediates, and energy carriers with clear annotations throughout.

Create a professional Krebs cycle (citric acid cycle) diagram showing all 8 steps in a circular pathway. Label each intermediate: acetyl-CoA entering, citrate, isocitrate, alpha-ketoglutarate, succinyl-CoA, succinate, fumarate, malate, oxaloacetate. Show enzymes at each step. Mark where NADH, FADH2, ATP, and CO2 are produced. Use color-coded arrows for different reaction types. Clean academic biochemistry textbook style, white background.

Simplified Krebs Cycle Overview

A beginner-friendly overview of the Krebs cycle that spotlights key inputs such as acetyl-CoA and NAD+ alongside outputs including NADH, FADH2, ATP, and CO2.

Create a simplified Krebs cycle diagram suitable for introductory biology. Show the cycle as a clean circular pathway with only the major intermediates (citrate, alpha-ketoglutarate, succinyl-CoA, oxaloacetate). Prominently display inputs: acetyl-CoA entering the cycle. Highlight outputs with icons: 3 NADH, 1 FADH2, 1 ATP/GTP, 2 CO2 per turn. Use bright, student-friendly colors. Clean modern educational style, white background.

Krebs Cycle with Enzymes

An enzyme-centered Krebs cycle layout that distinguishes the 8 catalytic enzymes at each step and calls out the key regulatory ones.

Create a detailed Krebs cycle diagram emphasizing the enzymes at each step. Highlight the 3 irreversible regulatory enzymes (citrate synthase, isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase) in bold red boxes. Show other enzymes (aconitase, succinyl-CoA synthetase, succinate dehydrogenase, fumarase, malate dehydrogenase) in blue boxes. Include substrate names and cofactors. Professional biochemistry reference style, white background.

Energy Carrier Focus Diagram

An energy-output view of the Krebs cycle that pinpoints exactly where NADH, FADH2, and ATP are generated at each reaction step.

Create a Krebs cycle diagram with special emphasis on energy carrier production. At each step where NADH is produced (steps 3, 4, 8), show a prominent green NADH badge. Where FADH2 is produced (step 6), show an orange FADH2 badge. Where GTP/ATP is produced (step 5), show a yellow ATP badge. Where CO2 is released (steps 3, 4), show red CO2 markers. Include a summary box: "Per turn: 3 NADH, 1 FADH2, 1 GTP, 2 CO2". Clean infographic style, white background.

What is the Krebs Cycle?

The Krebs cycle, also called the citric acid cycle or tricarboxylic acid (TCA) cycle, is a sequence of eight enzyme-driven reactions that take place inside the mitochondrial matrix of eukaryotic cells. First characterized by Hans Krebs in 1937, this metabolic pathway sits at the core of cellular respiration, acting as a junction between carbohydrate, fat, and protein catabolism. The cycle oxidizes acetyl-CoA (supplied by pyruvate, fatty acid, or amino acid breakdown) to release CO2 and generate the high-energy electron carriers NADH and FADH2. Those carriers then deliver electrons to the electron transport chain, powering ATP synthesis. Each complete revolution of the cycle consumes one two-carbon acetyl group and regenerates oxaloacetate so the process can begin again.

The 8 Steps of the Krebs Cycle

Step 1: Citrate synthase joins acetyl-CoA (2C) with oxaloacetate (4C) to yield citrate (6C), releasing coenzyme A

Step 2: Aconitase rearranges citrate into isocitrate through a paired dehydration and rehydration

Step 3: Isocitrate dehydrogenase removes a carbon from isocitrate to give alpha-ketoglutarate (5C), releasing CO2 and producing NADH

Step 4: Alpha-ketoglutarate dehydrogenase converts alpha-ketoglutarate into succinyl-CoA (4C), releasing CO2 and producing NADH

Step 5: Succinyl-CoA synthetase transforms succinyl-CoA into succinate while generating GTP (or ATP) via substrate-level phosphorylation

Step 6: Succinate dehydrogenase oxidizes succinate to fumarate, producing FADH2 (the only Krebs cycle enzyme embedded in the inner membrane)

Step 7: Fumarase adds water across fumarate to produce malate

Step 8: Malate dehydrogenase oxidizes malate back to oxaloacetate, generating the third NADH of the cycle

Key Molecules and Energy Output

A single turn of the Krebs cycle yields 3 NADH, 1 FADH2, 1 GTP (functionally equivalent to 1 ATP), and 2 CO2. Because one glucose molecule produces 2 acetyl-CoA molecules through pyruvate decarboxylation, the cycle completes two turns per glucose, totaling 6 NADH, 2 FADH2, and 2 GTP. The eight carbon-containing intermediates progress through 6-carbon forms (citrate, isocitrate), a 5-carbon intermediate (alpha-ketoglutarate), and four 4-carbon forms (succinyl-CoA, succinate, fumarate, malate) before returning to oxaloacetate. The electron carriers NADH and FADH2 transfer their electrons to the electron transport chain, which ultimately powers oxidative phosphorylation to generate roughly 30 to 32 ATP per glucose.

Connection to the Electron Transport Chain

The Krebs cycle operates in tight coordination with the electron transport chain (ETC) embedded in the inner mitochondrial membrane. NADH passes electrons to Complex I, while FADH2 passes electrons to Complex II (which is the same protein as succinate dehydrogenase from step 6). Electron flow through the ETC complexes drives proton pumping across the membrane, building an electrochemical gradient that spins ATP synthase. On average, each NADH supports formation of roughly 2.5 ATP and each FADH2 supports about 1.5 ATP via oxidative phosphorylation. If the ETC were blocked, the cycle would halt because there would be no free NAD+ or FAD available to accept electrons.

Classroom and Study Applications

Biochemistry courses: Build mastery of the full pathway covering enzymes, substrates, and regulatory control points

Biology exams: Use annotated diagrams to reinforce memory of intermediates and the steps that produce each energy carrier

Medical education: Understand disease states that arise from inherited or acquired deficiencies in Krebs cycle enzymes

Blank diagram worksheets: Gauge comprehension with fill-in-the-blank cycle templates that students complete independently

Comparative metabolism: Trace how the cycle intersects gluconeogenesis, amino acid biosynthesis, and fatty acid metabolism

Research presentations: Produce polished, accurate diagrams suitable for scientific papers and conference posters

Frequently asked questions

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