DNA and the genome — AQA GCSE Biology
Test yourself on DNA and the genome with AQA GCSE practice questions.
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DNA and the genome explained
DNA is the molecule that stores genetic information.
Read the full explanation
Its structure is a polymer of nucleotides, each containing a sugar, a phosphate group and a base. Two strands of nucleotides pair up by complementary bases (A with T, C with G) and twist around each other to form a double helix. The genome is the entire genetic material of an organism: in humans this is the complete set of DNA in the nucleus, including all genes and non-coding regions. When describing structure, link the repeating nucleotide units to the polymer backbone and the base pairing that holds the two strands together. When defining genome, state that it is the whole genetic material, not just the genes, and give a named example such as the human genome.
Your focus
- Describe DNA as a polymer of nucleotides forming a double helix.
- State the complementary base pairing rule A–T and C–G.
- Define genome as the entire genetic material of an organism.
DNA and the genome exam tips
Marking Points
- DNA is a polymer made of repeating nucleotide units.
- Each nucleotide contains a sugar, a phosphate group and a base.
- The bases pair specifically: adenine with thymine, and cytosine with guanine.
- Two strands of nucleotides form a double helix.
- The genome is the entire genetic material of an organism.
- The human genome includes all the DNA in the nucleus, not only the coding genes.
Examiner Tips
- 💡Use the terms nucleotide, complementary base pairing and double helix when describing structure.
- 💡When defining genome, include the word entire or complete to show it is all the genetic material.
- 💡Sketch a simple labelled diagram of the double helix with base pairs to support your written description.
Common Mistakes
- Saying that DNA is made of protein: correct this by stating that DNA is a nucleic acid polymer and proteins are made from the instructions carried by DNA.
- Describing the genome as only the genes: correct this by stating that the genome is all the genetic material, including non-coding DNA.
- Writing that the two strands are identical: correct this by explaining that the strands are complementary because of specific base pairing.