AQA · GCSE · Biology

    Course version: 8461 · Version from Sept 2018

    Students should be able to describe the structure of DNA and define genome.

    Full specification wording

    DNA and the genome: Students should be able to describe the structure of DNA and define genome.

    DNA is the molecule that stores genetic information.

    Checked against the AQA 8461 specification (opens in a new tab) on .

    • Point 1 of 9
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    DNA is the molecule that stores genetic information. 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.

    What earns the marks

    • 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.

    Common mistakes and how to put them right

    • Saying that DNA is made of protein.

      Put it right 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.

      Put it right by stating that the genome is all the genetic material, including non-coding DNA.

    • Writing that the two strands are identical.

      Put it right by explaining that the strands are complementary because of specific base pairing.

    Exam 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.

    Try the lesson

    The start of the DNA and the genome: Students should be able to describe the structure of DNA and define genome. lesson, made from checked teaching notes for this specification point.

    Have a go first

    Which statement best describes the structure of a DNA molecule?

    Listen

    DNA is the molecule that stores genetic information. 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. A strong answer earns marks for these 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. A common slip: Saying that DNA is made of protein. Instead, stating that DNA is a nucleic acid polymer and proteins are made from the instructions carried by DNA. Exam tip: Use the terms nucleotide, complementary base pairing and double helix when describing structure.

    See it

    A top-down flowchart. The first box says DNA is a polymer, which leads to a box saying repeating nucleotide units. That leads to a box saying nucleotide: sugar, phosphate group, base. This leads to a box saying complementary base pairing: A with T, C with G. That leads to a box saying two strands of nucleotides, which leads to a final box saying double helix. Separately, a box saying genome: entire genetic material of an organism leads to a box saying human genome: all the DNA in the nucleus, not only the coding genes.
    It shows how nucleotides build DNA into a double helix through complementary base pairing, and what the genome is.

    Key words

    Say what each word means before you turn the card.

    Complementary base pairing

    Try answering aloud or in your head before turning the card.

    The genome as the complete genetic material

    Try answering aloud or in your head before turning the card.

    Structure and function of biological molecules

    Try answering aloud or in your head before turning the card.

    Genetic information and inheritance

    Try answering aloud or in your head before turning the card.

    See every definition
    Complementary base pairing
    The bases pair specifically: adenine with thymine, and cytosine with guanine, which holds the two strands together.
    The genome as the complete genetic material
    The entire genetic material of an organism, including all genes and non-coding regions, not just the genes.
    Structure and function of biological molecules
    DNA is a polymer of nucleotides, each containing a sugar, a phosphate group and a base, and two strands form a double helix.
    Genetic information and inheritance
    DNA is the molecule that stores genetic information.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-down flowchart. The first box says DNA is a polymer, which leads to a box saying repeating nucleotide units. That leads to a box saying nucleotide: sugar, phosphate group, base. This leads to a box saying complementary base pairing: A with T, C with G. That leads to a box saying two strands of nucleotides, which leads to a final box saying double helix. Separately, a box saying genome: entire genetic material of an organism leads to a box saying human genome: all the DNA in the nucleus, not only the coding genes.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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