1
Triple onlyHigher tier
[1 mark]What decides the order of amino acids in a protein?
- The shape of the ribosome
- The order of bases in a gene
- The number of chromosomes in the cell
- The type of enzyme in the nucleus
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Answer: B B: The order of bases in a gene (1)
2
Triple onlyHigher tier
[3 marks]Explain how the order of bases in a gene decides the shape of an enzyme.
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- the order of bases decides the order of amino acids (1)
- the chain of amino acids folds (1)
- to produce a specifically shaped protein / active site (1)
3
Triple onlyHigher tier
[4 marks]Describe how a gene is used to make a polypeptide.
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- RNA polymerase binds to non-coding DNA in front of the gene (1)
- RNA polymerase produces a complementary mRNA strand (1)
- from the coding DNA of the gene (1)
- mRNA attaches to a ribosome (1)
- codons / triplets of bases in the mRNA code for specific amino acids (1)
- tRNA transfers amino acids to the ribosome (1)
- amino acids are linked to form a polypeptide (1)
- Max 4
4
Triple onlyHigher tier
[3 marks]A variant in the non-coding DNA in front of a gene alters the phenotype of an organism. The protein made from the gene has the same sequence of amino acids. Explain how the variant can affect the phenotype.
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- the variant affects the binding of RNA polymerase (1)
- so a different amount of mRNA is made (1)
- so the quantity of protein produced is altered (1)
5
Triple onlyHigher tier
[3 marks]A variant in the coding DNA of a gene for an enzyme stops the enzyme working. Explain how.
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- the sequence of amino acids is altered (1)
- so the protein folds into a different shape / the active site changes shape (1)
- the substrate no longer fits so the enzyme activity is reduced or lost (1)