---
title: "Mutations and Their Effect on Proteins"
description: "A change to one base may change one amino acid, and a changed amino acid may change the shape the protein folds into. Explains why most mutations do nothing while a few change everything."
canonical: https://lightmysky.com/learn/science/mutations-and-their-effect-on-proteins-mt_dTOQH3vGSz
source: https://lightmysky.com/learn/science/mutations-and-their-effect-on-proteins-mt_dTOQH3vGSz.md
retrieved: 2026-09-12
---

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# Mutations and Their Effect on Proteins

A change to one base may change one amino acid, and a changed amino acid may change the shape the protein folds into. Explains why most mutations do nothing while a few change everything.

Subject: Science · Area: Genetics & Evolution · Ages 15 to 16
Page: https://lightmysky.com/learn/science/mutations-and-their-effect-on-proteins-mt_dTOQH3vGSz

## Ready when they can

- Works out what a given single base change does to the amino acid sequence.
- Explains why a mutation in an enzyme's active site matters more than one further along the chain.
- Gives a reason why most mutations have no visible effect at all.

## Lesson: Small DNA changes, big protein effects

A mutation is a random change in DNA. A substitution swaps one base: sometimes nothing changes, sometimes one amino acid changes, sometimes a stop appears early. Insertions and deletions are more serious because they shift the whole reading frame and scramble every triplet downstream.

A changed amino acid can change the shape the protein folds into, and shape decides the job. A change inside an enzyme active site matters most, since the target no longer fits. Yet most mutations do nothing, because many land in silent stretches or swap in the same acid.

**Example.** Use this mini table: CAA and CAG both mean glutamine, while UAA means stop. Changing CAA to CAG is silent, since the acid stays glutamine. Changing CAA to UAA is severe, since the chain stops early and the enzyme never forms its active site.

**Tip.** Trace every mutation in order: name the type, find the new acid, judge the shape. Repair enzymes fix most slips, and mutagens such as UV and smoke raise the error rate, so errors that survive proofreading are rare.

**Recap.** Trace the base change to the acid change to the shape change to judge it.

## Practice

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

## Needs first

- [From Gene to Protein](https://lightmysky.com/learn/science/from-gene-to-protein-mt_PdNyzTl8Ye)
- [Genetic Mutation](https://lightmysky.com/learn/science/genetic-mutation-mt_rOqo-8GeKt)

## Opens up

- [Gene Mutations and Their Consequences](https://lightmysky.com/learn/science/gene-mutations-and-their-consequences-mt_CDcaL6-iVp)
- [Punnett Squares and Monohybrid Ratios](https://lightmysky.com/learn/science/punnett-squares-and-monohybrid-ratios-mt_T4ZC45-77w)