AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
(HT only) Students should be able to: • recall a simple description of…
Full specification wording
DNA structure (biology only): (HT only) Students should be able to: • recall a simple description of protein synthesis • explain simply how the structure of DNA affects the protein made • describe how genetic variants may influence phenotype: a) in coding DNA by altering the activity of a protein; and b) in non-coding DNA by altering how genes are expressed.
Protein synthesis begins when a gene's DNA base sequence is copied into a messenger molecule, which carries the code to a ribosome.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 8 of 19
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Protein synthesis begins when a gene's DNA base sequence is copied into a messenger molecule, which carries the code to a ribosome. There, the bases are read in triplets, and each triplet specifies an amino acid; the amino acids are joined in order to form a protein. The DNA base sequence therefore determines the amino acid sequence, which determines how the protein folds and functions. A genetic variant is a change in the DNA base sequence. In coding DNA, a variant can change the amino acid sequence, altering the protein's activity, for example changing an enzyme's active site so it no longer works. In non-coding DNA, a variant can alter how genes are expressed, for example by changing whether a gene is switched on or off, which changes the amount of protein made and so affects phenotype.
What earns the marks
- Protein synthesis: the DNA base sequence of a gene is copied into a messenger molecule, which carries the code to a ribosome where amino acids are joined in the correct order to form a protein.
- The order of bases in DNA determines the order of amino acids in a protein, and this order determines the protein's shape and function.
- A genetic variant is a change in the DNA base sequence; in coding DNA it can change the amino acid sequence and therefore alter the activity of the protein produced.
- An example of a coding DNA variant is a change in a gene for an enzyme that alters the active site, so the enzyme no longer catalyses its reaction.
- In non-coding DNA, a variant does not change the amino acid sequence of a protein but can alter how genes are expressed, for example by changing whether a gene is switched on or off.
- Altering gene expression changes the amount of protein made, which can influence the phenotype.
- Phenotype is the observable characteristics of an organism, resulting from the interaction of genotype and the environment.
Common mistakes and how to put them right
Thinking that non-coding DNA does not affect phenotype.
Put it right by explaining that non-coding DNA can control gene expression, so variants there can change how much protein is made and thus affect characteristics.
Believing that a change in DNA always changes the amino acid sequence.
Put it right by stating that variants in non-coding DNA do not alter the amino acid sequence but can alter gene expression.
Confusing the roles of DNA and messenger molecules in protein synthesis.
Put it right by describing DNA as the template that is copied, and the messenger molecule as the carrier of the code to the ribosome.
Exam tips
- Use the terms 'base sequence', 'amino acid sequence', 'protein shape' and 'protein function' in a logical chain when explaining how DNA structure affects the protein made.
- For variants, always state whether the DNA is coding or non-coding, then explain the consequence: altered protein activity for coding DNA, or altered gene expression for non-coding DNA.
- Practise writing a concise description of protein synthesis in no more than three or four steps, including the roles of the gene, the messenger molecule and the ribosome.
Try the lesson
The start of the DNA structure (biology only): (HT only) Students should be able to: • recall a simple description of protein synthesis • explain simply how the structure of DNA affects the protein made • describe how genetic variants may influence phenotype: a) in coding DNA by altering the activity of a protein; and b) in non-coding DNA by altering how genes are expressed. lesson, made from checked teaching notes for this specification point.
Have a go first
Which statement gives a simple description of protein synthesis?
Listen
Protein synthesis begins when a gene's DNA base sequence is copied into a messenger molecule, which carries the code to a ribosome. There, the bases are read in triplets, and each triplet specifies an amino acid; the amino acids are joined in order to form a protein. The DNA base sequence therefore determines the amino acid sequence, which determines how the protein folds and functions. A genetic variant is a change in the DNA base sequence. In coding DNA, a variant can change the amino acid sequence, altering the protein's activity, for example changing an enzyme's active site so it no longer works. In non-coding DNA, a variant can alter how genes are expressed, for example by changing whether a gene is switched on or off, which changes the amount of protein made and so affects phenotype. A strong answer earns marks for these points. Protein synthesis: the DNA base sequence of a gene is copied into a messenger molecule, which carries the code to a ribosome where amino acids are joined in the correct order to form a protein. The order of bases in DNA determines the order of amino acids in a protein, and this order determines the protein's shape and function. A genetic variant is a change in the DNA base sequence; in coding DNA it can change the amino acid sequence and therefore alter the activity of the protein produced. An example of a coding DNA variant is a change in a gene for an enzyme that alters the active site, so the enzyme no longer catalyses its reaction. A common slip: Thinking that non-coding DNA does not affect phenotype. Instead, explaining that non-coding DNA can control gene expression, so variants there can change how much protein is made and thus affect characteristics. Exam tip: Use the terms 'base sequence', 'amino acid sequence', 'protein shape' and 'protein function' in a logical chain when explaining how DNA structure affects the protein made.
Key words
Say what each word means before you turn the card.
protein synthesis
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genetic variant
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coding DNA
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non-coding DNA
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See every definition
- protein synthesis
- The DNA base sequence of a gene is copied into a messenger molecule, which carries the code to a ribosome where amino acids are joined in the correct order to form a protein.
- genetic variant
- A change in the DNA base sequence.
- coding DNA
- DNA in which a variant can change the amino acid sequence and therefore alter the activity of the protein produced.
- non-coding DNA
- DNA in which a variant does not change the amino acid sequence of a protein but can alter how genes are expressed.
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Test your understanding of DNA structure (biology only): (HT only) Students should be able to: • recall a simple description of protein synthesis • explain simply how the structure of DNA affects the protein made • describe how genetic variants may influence phenotype: a) in coding DNA by altering the activity of a protein; and b) in non-coding DNA by altering how genes are expressed.
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