---
title: "The Pentose Phosphate Pathway and Reducing Power for Biosynthesis"
description: "A branch off glycolysis produces the reduced carrier used for building molecules and for defending against oxidative damage, plus the five-carbon sugars needed for nucleotides. The cell adjusts the br"
canonical: https://lightmysky.com/learn/science/the-pentose-phosphate-pathway-and-reducing-power-for-biosynthesis-mt_2p-JnaEaTO
source: https://lightmysky.com/learn/science/the-pentose-phosphate-pathway-and-reducing-power-for-biosynthesis-mt_2p-JnaEaTO.md
retrieved: 2026-09-12
---

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# The Pentose Phosphate Pathway and Reducing Power for Biosynthesis

A branch off glycolysis produces the reduced carrier used for building molecules and for defending against oxidative damage, plus the five-carbon sugars needed for nucleotides. The cell adjusts the branch according to whether it needs reducing power, ribose or both.

Subject: Science · Area: Biochemistry & Molecular Biology · Ages 21 to 22
Page: https://lightmysky.com/learn/science/the-pentose-phosphate-pathway-and-reducing-power-for-biosynthesis-mt_2p-JnaEaTO

## Ready when they can

- Distinguishes the carrier used for biosynthesis from the one that feeds the electron transport chain.
- Explains what a rapidly dividing cell needs from this pathway.
- Links a deficiency in the first enzyme to red cells being vulnerable to oxidative stress.

## Lesson: The side loop that builds and shields

At glucose 6 phosphate, traffic can leave glycolysis for a side loop called the pentose phosphate pathway. Its gatekeeper is the first enzyme, glucose 6 phosphate dehydrogenase. The loop runs in two phases: an oxidative branch that makes the carrier NADPH, and a nonoxidative branch that shuffles sugars including ribose 5 phosphate. Leftover carbons rejoin glycolysis through shared intermediates, so nothing is wasted.

Your cells keep two reduced carriers because burning and building are different jobs. NADH feeds the electron transport chain to burn fuel for energy. NADPH instead powers reductive biosynthesis and antioxidant defence. The split is clean: NADPH builds and shields, NADH burns.

**Example.** Picture a cell about to divide. It must copy its whole genome, which needs ribose for new nucleotides, and it must double its membranes, which needs NADPH for lipid building plus antioxidant cover. So a dividing cell runs both branches hard, taking reducing power and building blocks together. Without the loop, division stalls for lack of raw material.

**Tip.** A faulty gatekeeper in G6PD deficiency starves cells of NADPH. Red blood cells suffer most because they carry no mitochondria and no backup NADPH source, leaving them open to oxidative damage.

**Recap.** One side loop off glycolysis supplies NADPH for building and defence plus ribose for genomes.

## Practice

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

## Opens up

- [Transamination, Ammonia and the Urea Cycle](https://lightmysky.com/learn/science/transamination-ammonia-and-the-urea-cycle-mt_MFu5uQKyFL)