---
title: "Glycolysis and the Link Reaction"
description: "Glucose is split into two pyruvate molecules in the cytoplasm, with a small net ATP gain and no oxygen involved. Pyruvate then enters the mitochondrion and becomes acetyl coenzyme A."
canonical: https://lightmysky.com/learn/science/glycolysis-and-the-link-reaction-mt_crbadbBvqB
source: https://lightmysky.com/learn/science/glycolysis-and-the-link-reaction-mt_crbadbBvqB.md
retrieved: 2026-09-12
---

> **Agent view.** This is the Markdown twin of the page, for tools and assistants.
> When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md
> API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md
> Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt
> Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json
> Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`.

# Glycolysis and the Link Reaction

Glucose is split into two pyruvate molecules in the cytoplasm, with a small net ATP gain and no oxygen involved. Pyruvate then enters the mitochondrion and becomes acetyl coenzyme A.

Subject: Science · Area: Organisms & Life Processes · Ages 16 to 18
Page: https://lightmysky.com/learn/science/glycolysis-and-the-link-reaction-mt_crbadbBvqB

## Ready when they can

- Explains why glycolysis spends ATP before it yields any.
- States the net ATP and reduced NAD yield per glucose molecule.
- Says what is removed from pyruvate in the link reaction and where that happens.

## Lesson: Splitting sugar for quick energy

Glycolysis opens respiration in the cytoplasm, breaking sugar to release energy for work such as movement, with no oxygen needed. One glucose is primed with two ATP, split into two three-carbon pieces, then oxidised into two pyruvates. The payoff banks four ATP and two reduced NAD, so after the two ATP entry fee the net gain is two ATP plus two reduced NAD.

Pyruvate cannot enter the next stage as it is, so the link reaction rebuilds it. Each pyruvate crosses into the mitochondrial matrix, loses carbon dioxide, and passes hydrogen to NAD. The leftover two-carbon acetyl group joins coenzyme A as acetyl CoA. Per glucose this runs twice, giving two carbon dioxides and two reduced NAD.

**Example.** Keep a running tally per glucose. Glycolysis nets two ATP and two reduced NAD in the cytoplasm. The link step adds two carbon dioxides and two more reduced NAD in the matrix. Small gains now, bigger payoffs later. When oxygen runs short, fermentation recycles NAD in the cytoplasm so glycolysis keeps going.

**Tip.** A cell with no mitochondria still runs glycolysis, since the pathway lives in the cytoplasm. Fermenters recycle NAD in the cytoplasm to keep it spinning, while aerobes ship pyruvate toward the later stages.

**Recap.** Split glucose to two pyruvates for a net two ATP, then trim each pyruvate to acetyl CoA in the matrix.

## Practice

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

## Needs first

- [Respiration: Energy Yield, Oxygen Debt and Fermentation](https://lightmysky.com/learn/science/respiration-energy-yield-oxygen-debt-and-fermentation-mt_mvnCjThdTH)
- [The Calvin Cycle and Carbon Fixation](https://lightmysky.com/learn/science/the-calvin-cycle-and-carbon-fixation-mt_zGOCx9mNrx)

## Opens up

- [Control Points in Glycolysis and the Committed Step](https://lightmysky.com/learn/science/control-points-in-glycolysis-and-the-committed-step-mt_2vAoKtnmoz)
- [The Krebs Cycle and the Reduced Carriers](https://lightmysky.com/learn/science/the-krebs-cycle-and-the-reduced-carriers-mt_eviWcVke2x)