Learning Objective

In this lesson we will learn about the structure of DNA – the molecule that carries genetic information in living things.

Learning Outcomes

By the end of this lesson you will be able to:

  • Describe the structure of nucleotides – the subunits of DNA molecules.
  • Describe the structure of DNA molecules, including:
  • The types of bonds that hold DNA molecules together.
  • The base-pairing rules in DNA.
  • DNA’s double helix structure.
  • Explain how DNA molecules carry a ‘genetic code’.

dna the molecule of life lesson contents

(Image: luchschenF, Adobe Stock)

Lesson Topics

1 | DNA in Cells

2 | Nucleotides – The Subunits of DNA

3 | DNA Molecules

4 | Base-Pairing in DNA

5 | DNA Double Helix

6 | The Genetic Code


Lesson Summary

  • Living things carry genetic information in large molecules called DNA (deoxyribonucleic acid ), which is packaged into chromosomes in the nuclei of cells.
  • DNA molecules are made up of subunits called nucleotides, which consist of a sugar, a base and a phosphate.
  • There are four different nucleotides in DNA, each with a different base – G, C, A or T.
  • Nucleotides can join together in two ways.
  • Firstly, nucleotides can join by phosphodiester bonds (covalent bonds) between sugars and phosphates, resulting in single-stranded DNA.
  • Secondly, nucleotides can join by hydrogen bonds (weaker bonds) between bases, resulting in double-stranded DNA.
  • The hydrogen bonding between bases on different strands of DNA occurs according to the base-pairing rules – only G-C and A-T pairs can form.
  • Double-stranded DNA molecules have a twisted structure known as a double helix.
  • The order of the four different nucleotides in DNA molecules determines the genetic make-up of an organism.

dna double helix animation

(Image: brian0918, Wikimedia Commons)

(Header image: svetlaborovko, Adobe Stock)


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