The effect of base-pair substitution mutations on protein function varies widely from no detectable effect to the complete loss of protein function (null allele).
Part A Why do the functional consequences of base-pair substitution vary so widely? Select the four correct answers.
1. Nucleotide substitutions might not cause changes in the amino acid sequence of the protein.
2. The reading frame of the gene could be affected by base-pair substitution mutations, which almost always leads to lack of function.
3. Nucleotide substitutions in exons always lead to changes of amino acids in the protein.
4. The reading frame of the gene could be affected by base-pair substitution mutations, which rarely leads to lack of function.
5. Missense mutations create amino acid substitutions, which might affect protein functionality.
6. Mutations that occur in the intron sequences generally do not affect protein functionality.
The effect of base-pair substitution mutations on protein function varies widely from no detectable effect to the complete loss of protein function (null allele).
Part A Why do the functional consequences of base-pair substitution vary so widely? Select the four correct answers.
1. Nucleotide substitutions might not cause changes in the amino acid sequence of the protein.
2. The reading frame of the gene could be affected by base-pair substitution mutations, which almost always leads to lack of function.
3. Nucleotide substitutions in exons always lead to changes of amino acids in the protein.
4. The reading frame of the gene could be affected by base-pair substitution mutations, which rarely leads to lack of function.
5. Missense mutations create amino acid substitutions, which might affect protein functionality.
6. Mutations that occur in the intron sequences generally do not affect protein functionality.
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Part B
Think about the DNA coding sequence of a gene. If an A were swapped for a T, what kind of mutation could it cause and why?
| a) It could cause a frameshift nonsense or frameshift missense mutation because it would change the reading frame of the codon triplet. | ||||||||||||||||||||||||||||
| b) It could cause a silent, missense, or nonsense mutation because those are the types that can be caused by a nucleotide-pair substitution like this one. | ||||||||||||||||||||||||||||
| c) It could cause a nonsense mutation because the sequence would no longer be the same, so the protein would be shorter and non-functional. | ||||||||||||||||||||||||||||
| d) It could cause a silent mutation because A and T are complementary to each other so it is not really a substitution mutation. Part C Why is a frameshift missense mutation more likely to have a severe effect on phenotype than a nucleotide-pair substitution missense mutation in the same protein?
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