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Problem 1
In this chapter, we focused on how gene mutations arise and how cells repair DNA damage. At the same time, we found opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter,
How do we know that mutations occur randomly?- In this chapter, we focused on how gene mutations arise and how cells repair DNA damage. At the same time, we found opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, How do we know that certain chemicals and wavelengths of radiation induce mutations in DNA?
Problem 1
- In this chapter, we focused on how gene mutations arise and how cells repair DNA damage. At the same time, we found opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, How do we know that DNA repair mechanisms detect and correct the majority of spontaneous and induced mutations?
Problem 1
- Write a short essay contrasting how these concepts may differ between bacteria and eukaryotes.
Problem 2
Problem 3
Price et al. [(1999). J. Bacteriol. 181:2358–2362] conducted a genetic study of the toxin transport protein (PA) of Bacillus anthracis, the bacterium that causes anthrax in humans. Within the 2294-nucleotide gene in 26 strains they identified five point mutations—two missense and three synonyms—among different isolates. Necropsy samples from an anthrax outbreak in 1979 revealed a novel missense mutation and five unique nucleotide changes among ten victims. The authors concluded that these data indicate little or no horizontal transfer between different B. anthracis strains.
Which types of nucleotide changes (missense or synonyms) cause amino acid changes?Problem 3
Price et al. [(1999). J. Bacteriol. 181:2358–2362] conducted a genetic study of the toxin transport protein (PA) of Bacillus anthracis, the bacterium that causes anthrax in humans. Within the 2294-nucleotide gene in 26 strains they identified five point mutations—two missense and three synonyms—among different isolates. Necropsy samples from an anthrax outbreak in 1979 revealed a novel missense mutation and five unique nucleotide changes among ten victims. The authors concluded that these data indicate little or no horizontal transfer between different B. anthracis strains.
On what basis did the authors conclude that evidence of horizontal transfer is absent from their data?- What is a spontaneous mutation, and why are spontaneous mutations rare?
Problem 3
Problem 4
Why would a mutation in a somatic cell of a multicellular organism not necessarily result in a detectable phenotype?
Problem 5
Most mutations are thought to be deleterious. Why, then, is it reasonable to state that mutations are essential to the evolutionary process?
Problem 6
Why is a random mutation more likely to be deleterious than beneficial?
Problem 7
Most mutations in a diploid organism are recessive. Why?
Problem 8
What is the difference between a silent mutation and a neutral mutation?
- When the amino acid sequences of insulin isolated from different organisms were determined, differences were noted. For example, alanine was substituted for threonine, serine for glycine, and valine for isoleucine at corresponding positions in the protein. List the single-base changes that could occur in codons of the genetic code to produce these amino acid changes.
Problem 8
- Describe a tautomeric shift and how it may lead to a mutation.
Problem 9
- In studies of the amino acid sequence of wild-type and mutant forms of tryptophan synthetase in E. coli, the following changes have been observed: Determine a set of triplet codes in which only a single-nucleotide change produces each amino acid change.
Problem 9
- Contrast and compare the mutagenic effects of deaminating agents, alkylating agents, and base analogs.
Problem 10
Problem 11
Why are frameshift mutations likely to be more detrimental than point mutations, in which a single pyrimidine or purine has been substituted?
Problem 12
Why are X rays more potent mutagens than UV radiation?
- DNA damage brought on by a variety of natural and artificial agents elicits a wide variety of cellular responses involving numerous signaling pathways. In addition to the activation of DNA repair mechanisms, there can be activation of pathways leading to apoptosis (programmed cell death) and cell-cycle arrest. Why would apoptosis and cell-cycle arrest often be part of a cellular response to DNA damage?
Problem 13
Problem 14
A glycine residue is in position 210 of the tryptophan synthetase enzyme of wild-type E. coli. If the codon specifying glycine is GGA, how many single-base substitutions will result in an amino acid substitution at position 210? What are they? How many will result if the wild-type codon is GGU?
- Contrast the various types of DNA repair mechanisms known to counteract the effects of UV radiation. What is the role of visible light in repairing UV-induced mutations?
Problem 14
Problem 15
Refer to Figure 13.7 to respond to the following:
A base-substitution mutation that altered the sequence shown in part (a) eliminated the synthesis of all but one polypeptide. The altered sequence is shown here:
5'-AUGCAUACCUAUGUGACCCUUGGA-3'
Determine why.- The family of a sixth-grade boy in Palo Alto, California, was informed by school administrators that he would have to transfer out of his middle school because they believed his mutation of the CFTR gene, which does not produce any symptoms associated with cystic fibrosis, posed a risk to other students at the school who have cystic fibrosis. After missing 11 days of school, a settlement was reached to have the boy return to school. What ethical problems might you associate with this example?
Problem 15
Problem 16
A significant number of mutations in the HBB gene that cause human β-thalassemia occur within introns or in upstream noncoding sequences. Explain why mutations in these regions often lead to severe disease, although they may not directly alter the coding regions of the gene.
Problem 16
Dominant mutations can be categorized according to whether they increase or decrease the overall activity of a gene or gene product. Although a loss-of-function mutation (a mutation that inactivates the gene product) is usually recessive, for some genes, one dose of the normal gene product, encoded by the normal allele, is not sufficient to produce a normal phenotype. In this case, a loss-of-function mutation in the gene will be dominant, and the gene is said to be haploinsufficient. A second category of dominant mutation is the gain-of-function mutation, which results in a new activity or increased activity or expression of a gene or gene product. The gene therapy technique currently being used in clinical trials involves the 'addition' to somatic cells of a normal copy of a gene. In other words, a normal copy of the gene is inserted into the genome of the mutant somatic cell, but the mutated copy of the gene is not removed or replaced. Will this strategy work for either of the two aforementioned types of dominant mutations?
- Contrast the structure of SINE and LINE DNA sequences. Why are LINEs referred to as retrotransposons?
Problem 16
Problem 17
In 2013 the actress Angelina Jolie elected to have prophylactic double-mastectomy surgery to prevent breast cancer based on a positive test for mutation of the BRCA1 gene. What are some potential positive and negative consequences of this high-profile example of acting on the results of a genetic test?
- Describe how the Ames test screens for potential environmental mutagens. Why is it thought that a compound that tests positively in the Ames test may also be carcinogenic?
Problem 17
- It has been shown that infectious agents such as viruses often exert a dramatic effect on their host cell's genome architecture. In many cases, viruses induce methylation of host DNA sequences in order to enhance their infectivity. What specific host gene functions would you consider as strong candidates for such methylation by infecting viruses?
Problem 18
- What genetic defects result in the disorder xeroderma pigmentosum (XP) in humans? How do these defects create the phenotypes associated with the disorder?
Problem 18
