AQA GCSE Combined Science: Biology

Revision Notes

6.1.4 DNA & the Genome

The Genome

  • The entire set of the genetic material of an organism is known as its genome
  • Biologists now know the entire human genome (they have worked out all the genes that are found in humans)

The Structure of DNA

  • The genetic material in the nucleus of a cell is composed of a chemical called DNA
  • DNA, or deoxyribonucleic acid, is the molecule that contains the instructions for growth and development of all organisms
  • DNA is a polymer made up of two strands forming a double helix
  • DNA is contained in structures called chromosomes
  • Chromosomes are located in the nucleus of cells

DNA, genes and chromosomes, IGCSE & GCSE Biology revision notes

Genes are short lengths of DNA that code for a protein. They are found on chromosomes


  • A gene is a short length of DNA found on a chromosome
  • Each gene codes for a particular sequence of amino acids
  • These sequences of amino acids form different types of proteins
  • There are many different types of proteins but some example of these could be:
    • structural proteins such as collagen found in skin cells
    • enzymes
    • hormones
  • Genes control our characteristics as they code for proteins that play important roles in what our cells do

The Human Genome Project

  • The Human Genome Project (completed in 2003) was the name of the international, collaborative research effort to determine the DNA sequence of the entire human genome and record every gene in human beings
  • This was a very important breakthrough for several reasons:
    • From a medical perspective, as it has already and will continue to improve our understanding of the genes linked with different types of disease and inherited genetic disorders, as well as the help us in finding treatments
    • The human genome has also made it possible to study human migration patterns from the past, as different populations of humans living in different parts of the world have developed very small differences in their genomes!

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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