---
title: "The Krebs Cycle and the Reduced Carriers"
description: "Acetyl coenzyme A enters a cycle that releases carbon dioxide and loads electrons onto NAD and FAD. The cycle makes almost no ATP directly; its real output is the reduced carriers."
canonical: https://lightmysky.com/learn/science/the-krebs-cycle-and-the-reduced-carriers-mt_eviWcVke2x
source: https://lightmysky.com/learn/science/the-krebs-cycle-and-the-reduced-carriers-mt_eviWcVke2x.md
retrieved: 2026-09-12
---

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# The Krebs Cycle and the Reduced Carriers

Acetyl coenzyme A enters a cycle that releases carbon dioxide and loads electrons onto NAD and FAD. The cycle makes almost no ATP directly; its real output is the reduced carriers.

Subject: Science · Area: Organisms & Life Processes · Ages 17 to 18
Page: https://lightmysky.com/learn/science/the-krebs-cycle-and-the-reduced-carriers-mt_eviWcVke2x

## Ready when they can

- Counts the carbon dioxide molecules released per turn and per glucose molecule.
- Explains what reduced NAD and reduced FAD are carrying.
- Says why the cycle is described as the main source of reduced carriers rather than of ATP.

## Lesson: The Carrier Factory

The Krebs cycle runs in the mitochondrial matrix. Acetyl CoA from the link reaction joins oxaloacetate to make citrate. Two carbons leave as carbon dioxide across the turn. Oxaloacetate is reborn at the end, ready for the next acetyl.

Each turn banks three reduced NAD, one reduced FAD, and a single ATP. Reduced NAD and FAD carry hydrogen and high energy electrons to the electron transport chain, where they fund most of the ATP of respiration. Double those numbers for one glucose, because glucose sends two acetyl groups through the cycle. Across its two turns, one glucose releases four carbon dioxides in total.

**Example.** Read the cycle as a carrier factory, not an ATP machine. Its direct ATP is tiny, but the carriers it loads earn the bulk of the ATP later at the chain. That division of labour is the whole point of the cycle.

**Tip.** Count carbons to check your work. Glucose brings six, the link reaction spends two as carbon dioxide, and the two turns release the last four. Every carbon you breathe out took this route.

**Recap.** Acetyl enters, carbon dioxide leaves, and the real payoff is the haul of reduced carriers for the chain.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Glycolysis and the Link Reaction](https://lightmysky.com/learn/science/glycolysis-and-the-link-reaction-mt_crbadbBvqB)

## Opens up

- [Oxidative Phosphorylation and Chemiosmosis](https://lightmysky.com/learn/science/oxidative-phosphorylation-and-chemiosmosis-mt_1wP3-14Y4V)
- [The Citric Acid Cycle as a Hub, and Refilling It](https://lightmysky.com/learn/science/the-citric-acid-cycle-as-a-hub-and-refilling-it-mt_BPPfI-vnab)