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Structure of the Double Helix

Structure of the Double Helix

Double helix is the description of the structure of a DNA molecule. A DNA molecule consists of two strands that wind around each other like a twisted ladder. Each strand has a backbone made of alternating groups of sugar (deoxyribose) and phosphate groups. Attached to each sugar is one of four bases: adenine (A), cytosine (C), guanine (G), or thymine (T). The two strands are held together by bonds between the bases, adenine forming a base pair with thymine, and cytosine forming a base pair with guanine.

Structure of the Double Helix
Images and animations are courtesy of the National Human Genome Research Institute's Talking Glossary (

Materials for Structure of the Double Helix


DNA - The Double Helix

Description: Explore a double helix using the Molecular Workbench software.

DNA Structure

Description: An animation and quiz on the structure of DNA


Profiles in Science: The Francis Crick Papers

Description: Information on the discovery of the double helix

Unraveling the Double Helix

Description: The discovery of the structure of DNA by James Watson and Francis Crick in 1953 is one of the most famous scientific discoveries of all time.



Description: This game combines the challenge of a scavenger hunt with the human genome. It allows anyone to create up to 20 walkable paths that explore the human genome with over 150 challenging questions, a leaderboard and themed paths. GenomeCache combines clues, fun facts and trivia questions to create an engaging learning experience.

Stretching DNA

Description: Explore stretching just a single strand of DNA using optical tweezers or fluid flow. Experiment with the forces involved and measure the relationship between the stretched DNA length and the force required to keep it stretched. Is DNA more like a rope or like a spring?

Interactive Tutorials

A Half DNA Ladder is a Template for Copying the Whole

Description: An interactive Web site exploring basic concepts of the DNA replication through historical discovery

Build a DNA Molecule

Description: Practice building a DNA molecule using this interactive tutorial on complementary base paring of DNA nucleotides.

Molecules App

Description: An app that allows you to view three-dimensional renderings of molecules and manipulate them using your fingers.

The DNA Molecule is Shaped Like a Twisted Ladder

Description: An interactive Web site exploring basic concepts of the Double Helix through historical discovery

Teacher Resources

Origami DNA (Lesson Plans/Lesson Activities)

Description: This activity brings to life the double helix structure of DNA by enabling your students to make their own paper model. Instructions and model templates are available for download.

Teacher Guide - Have Your DNA and Eat It Too (PDF 266.17 KB, Lesson Plans/Lesson Activities)

Description: Lesson plan on the structure of DNA and a class activity building an edible double helix

Yummy Gummy DNA

Description: Make your own edible DNA double helix out of sweets.


Discovering the Double Helix

Description: A history and video interviews with scientist about the discovery of the double helix

The Double Helix

Description: A video history on the discovery of the double helix