---
title: "Secondary Structure — AP Bio Definition & Exam Guide"
description: "Secondary structure is the local folding of a protein's backbone into alpha-helices and beta-sheets via hydrogen bonds, a key level of enzyme structure on the AP Bio exam."
canonical: "https://fiveable.me/ap-bio/key-terms/secondary-structure"
type: "key-term"
subject: "AP Biology"
---

# Secondary Structure — AP Bio Definition & Exam Guide

## Definition

The secondary structure refers to how those sequences or strings (primary structures) fold upon themselves due to hydrogen bonding between backbone elements. Common forms include alpha-helices and beta-sheets.

## Related Study Guides

- [3.1 Enzymes](/ap-bio/unit-3/enzyme-structure/study-guide/jsjBfuk2jmYAZVrmVwtF)

## Review

### Related Terms

- Alpha-Helix: This is a common secondary structure in proteins where the polypeptide chain forms a spiral shape, stabilized by hydrogen bonds. It's like twisting your string into a spring-like shape.
- Beta-Sheet: Another common secondary structure in proteins where parts of the polypeptide chain align parallel or antiparallel next to each other, forming sheet-like structures. Picture folding your string back-and-forth onto itself.
- Hydrogen Bonding: A weak bond between two molecules resulting from an electrostatic attraction between a proton in one molecule and an electronegative atom in the other. It's like the magnetic attraction that helps our bead string hold its shape.