Biology 1002B Chapter Notes - Chapter 6: Missense Mutation, Nonsense Mutation, Reading Frame
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5). The table shows five different mutations of a small section of a gene.
Use the base-pairing rules to complete the second column. For each mutation, write the sequence for any mRNA codons that will be changed as a result of the mutation in bold. Write any codons that wonât be changed in regular font.
Using the genetic code chart from question #3, identify any stop codons in the mRNA molecules â write these codons in red
For each mutation, write any amino acids that will be changed in the last column in bold font. Use red XXXs to indicate any amino acids that will be missing as a result of stop codons and use use regular font indicate any amino acids that will not be changed.
| DNA (Template Strand) | mRNA codon | Polypeptide |
| Original DNA = GCAAGTACCTGA | CGU UCA UGG ACU | arg â ser â trp â thr |
| Mutation = GCCAGTACCTGA (nucleotide change underlined) | ____ ____ ____ ____ | ___ ___ ___ ___ |
| Mutation = GCACGTACCTGA (nucleotide change underlined) | ____ ____ ____ ____ | ___ ___ ___ ___ |
| Mutation = GCAAGTACTTGA (nucleotide change underlined) | ____ ____ ____ ____ | ___ ___ ___ ___ |
| Mutation = GAAGTACCTGA (first C deleted) | ____ ____ ____ ____ | ___ ___ ___ ___ |
| Mutation = GCAAGTACTGA (second C deleted) | ____ ____ ____ ____ | ___ ___ ___ ___ |
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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Fill in the blank. Elongation during translation does NOT involve ____________.
Question 16 options:
| the translation of codons according to the genetic code | |
| the formation of bonds catalyzed by the ribosome | |
| complementary base pairing between RNA molecules | |
| amino acids being linked together in a polypeptide | |
| reading the DNA template 3' to 5' |
For a given gene, what establishes the reading frame for translation?
Question 17 options:
| the location of the enhancer relative to the gene | |
| the first three nucleotides at the 5' end of the mRNA | |
| the first three nucleotides at the 3' end of the mRNA | |
| the start codon in the mRNA | |
| the location of the promoter relative to the gene |
Which of the following is the LEAST likely direct consequence of a substitution mutation?
Question 18 options:
| changing the length of a protein coded for by a gene | |
| changing one amino acid in a protein | |
| creating a stop codon | |
| eliminating a start codon | |
| changing the length of the DNA molecule containing a gene |
Suppose that the pre-mRNA transcript from a eukaryotic gene is 30,000 nucleotides long, and the gene codes for a sequence of 300 amino acids. What is the best explanation for the relationship between these numbers?
Question 19 options:
| only the first 900 nucleotides of the pre-mRNA transcript are translated | |
| it takes 100 nucleotides to specify a single amino acid | |
| 300 of the nucleotides in the transcript are important, and the rest are "junk" | |
| only the last 900 nucleotides of the pre-mRNA transcript are translated | |
| large portions of pre-mRNA transcripts are cut out during RNA processing |
Suppose an individual is born into a population with a novel mutation. Is the new mutation an evolutionary change, and why?
Question 20 options:
| no, because it is not a big enough change to count | |
| yes, because new mutations are always adaptive | |
| yes, because the appearance of a new genetic variant is a genetic change in a population | |
| no, because not enough individuals have the mutation for it to matter | |
| no, because most mutations are not adaptive |