AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
A gene is a small section of DNA on a chromosome. Each gene codes for a…
Full specification wording
DNA and the genome: A gene is a small section of DNA on a chromosome. Each gene codes for a particular sequence of amino acids, to make a specific protein.
A gene is a small section of DNA found on a chromosome.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 3 of 8
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A gene is a small section of DNA found on a chromosome. The order of the bases along that section of DNA is a code. Each gene codes for a particular sequence of amino acids, and the amino acids are joined together in that order to make a specific protein. Different genes have different base sequences, so they code for different amino acid sequences and therefore different proteins. For example, one gene may code for the protein haemoglobin, while another codes for an enzyme such as amylase. Because a chromosome contains many genes, one chromosome carries the instructions for making many different proteins. The proteins produced determine many of the characteristics of an organism.
What earns the marks
- A gene is a small section of DNA located on a chromosome.
- Each gene codes for a particular sequence of amino acids.
- The sequence of amino acids determines the specific protein that is made.
- Different genes code for different proteins because they have different base sequences.
- A chromosome contains many genes, so it carries instructions for many proteins.
- The order of amino acids in a protein is controlled by the gene, and this affects the protein's shape and function.
Common mistakes and how to put them right
Saying a gene codes for an amino acid.
Put it right by stating that a gene codes for a sequence of amino acids that forms a protein.
Saying a gene is a whole chromosome.
Put it right by stating that a gene is a small section of DNA on a chromosome.
Saying a gene codes for a protein directly without mentioning amino acids.
Put it right by including the sequence of amino acids as the link between the gene and the protein.
Exam tips
- Link the three ideas in order: gene, sequence of amino acids, specific protein, so your answer shows the full chain of reasoning.
- Use the phrase 'particular sequence of amino acids' rather than 'amino acids' alone, because the sequence is what makes each protein specific.
- If asked why different cells make different proteins, refer to which genes are expressed rather than saying the genes are different, unless the question is about different organisms.
Try the lesson
The start of the DNA and the genome: A gene is a small section of DNA on a chromosome. Each gene codes for a particular sequence of amino acids, to make a specific protein. lesson, made from checked teaching notes for this specification point.
Have a go first
What is a gene? Select the correct answer.
Listen
A gene is a small section of DNA found on a chromosome. The order of the bases along that section of DNA is a code. Each gene codes for a particular sequence of amino acids, and the amino acids are joined together in that order to make a specific protein. Different genes have different base sequences, so they code for different amino acid sequences and therefore different proteins. For example, one gene may code for the protein haemoglobin, while another codes for an enzyme such as amylase. Because a chromosome contains many genes, one chromosome carries the instructions for making many different proteins. The proteins produced determine many of the characteristics of an organism. A strong answer earns marks for these points. A gene is a small section of DNA located on a chromosome. Each gene codes for a particular sequence of amino acids. The sequence of amino acids determines the specific protein that is made. Different genes code for different proteins because they have different base sequences. A common slip: Saying a gene codes for an amino acid. Instead, stating that a gene codes for a sequence of amino acids that forms a protein. Exam tip: Link the three ideas in order: gene, sequence of amino acids, specific protein, so your answer shows the full chain of reasoning.
Key words
Say what each word means before you turn the card.
Gene
Try answering aloud or in your head before turning the card.
Amino acid sequence
Try answering aloud or in your head before turning the card.
Protein
Try answering aloud or in your head before turning the card.
Chromosome
Try answering aloud or in your head before turning the card.
See every definition
- Gene
- A small section of DNA on a chromosome that codes for a particular sequence of amino acids to make a specific protein.
- Amino acid sequence
- The particular order of amino acids coded for by a gene, which determines the specific protein that is made.
- Protein
- A molecule made when amino acids are joined together in the order coded for by a gene.
- Chromosome
- A structure that contains many genes, so it carries the instructions for making many different proteins.
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of DNA and the genome: A gene is a small section of DNA on a chromosome. Each gene codes for a particular sequence of amino acids, to make a specific protein.
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge