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Krebs Cycle Explorer

Run the Krebs Cycle Explorer MicroSim Fullscreen

About This MicroSim

This MicroSim provides an interactive step-through visualization of the Krebs cycle (citric acid cycle), the central metabolic pathway that oxidizes acetyl-CoA to \(\ce{CO2}\) while generating electron carriers (\(\ce{NADH}\) and \(\ce{FADH2}\)) and a small amount of ATP. The cycle's eight intermediates are arranged in a circular layout with product badges on each reaction arrow.

How to Use

  1. Step Forward — Click to advance through the cycle one reaction at a time. Each step highlights the active reaction arrow and updates the running tally of products (CO₂, NADH, FADH₂, ATP).
  2. Run Full Cycle — Automatically animates all 8 steps in sequence.
  3. Reset — Returns the cycle to its initial state and clears the tally.
  4. ×2 for glucose — Toggles the tally between "per turn" and "per glucose" (since each glucose produces 2 acetyl-CoA and thus 2 turns of the cycle).
  5. Click any intermediate node — Shows its name, carbon count, and biological role in an info panel.

Iframe Embed Code

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<iframe src="https://dmccreary.github.io/biology/sims/krebs-cycle-explorer/main.html"
        height="655"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Grade Level

9-12 (AP Biology)

Duration

10-15 minutes

Prerequisites

  • Understanding of glycolysis and acetyl-CoA formation
  • Basic knowledge of oxidation-reduction reactions
  • Familiarity with ATP, NADH, and FADH₂ as energy carriers

Activities

  1. Exploration (5 min): Step through the cycle one reaction at a time. For each step, read the reaction description and note which products are generated.
  2. Guided Practice (5 min): Toggle "×2 for glucose" and compare the per-turn vs. per-glucose product totals. Click each intermediate to review its carbon count and role.
  3. Assessment (5 min): Without looking at the MicroSim, predict the total products of one turn of the Krebs cycle. Then verify using the step-through.

Assessment

  • Students can list all 8 intermediates in order
  • Students can identify which steps release \(\ce{CO2}\), produce NADH, produce FADH₂, or produce ATP
  • Students can calculate total products per glucose molecule (2 turns)

References

  1. Krebs Cycle — Wikipedia
  2. Campbell Biology, 12th Edition, Chapter 9: Cellular Respiration