Cell Bio: Genetics Ch. 12 – Flashcards
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Which structures can be involved in recombination?
a. Chromatids of nonhomologous chromosomes
b. Chromosomes in different cells
c. Any two chromosomes
d. Chromatids of homologous chromosomes
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d. Chromatids of homologous chromosomes. Chromatids of homologous chromosomes can recombine during meiosis.
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The process that determines the length of heteroduplex DNA on the chromatids is called branch migration.
T or F
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True. The crossbridge DNA structure formed after the initial nick is sealed can migrate along the chromatid. This process is called branch migration, and it increases the length of heteroduplex DNA.
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Which process does not occur during recombination?
a. Ligation
b. Nicking of the sugar‑phosphate backbone
c. DNA polymerization
d. Strand displacement
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c. DNA polymerization. Recombination does not include the synthesis of new DNA.
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Definition of point mutation.
-There are 2 types
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An error in replication.
-frameshift or base-pair substitution mutations.
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Frameshift mutation
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A mutant polypeptide contains an altered amino acid sequence from the point of mutation to the end of the polypeptide. A frameshift mutation can occur if the DNA polymerase leaves out a nucleotide or adds an extra nucleotide to the sequence.
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Base-pair substitution mutation
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The replacement of one nucleotide base pair by another. A base substitution mutation can occur if the DNA polymerase inserts the wrong nucleotide base as it synthesizes a new strand of DNA.
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Nonsense mutation
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A base-pair substitution that creates a stop codon in place of a codon specifying an amino acid.
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Missense mutation
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A base-pair substitution that results in an amino acid change to the protein.
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Silent mutation
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A base-pair substitution producing an mRNA codon specifying the same amino acid as the wild-type mRNA.
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Generally speaking, which of the following mutations would most severely affect the protein coded for by a gene?
a. a base substitution at the beginning of the gene
b. a base substitution at the end of the gene
c. a frameshift deletion at the beginning of the gene
d. a frameshift deletion at the end of the gene
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c. A frameshift deletion at the beginning of the gene. A frameshift mutation at the beginning of a gene would affect every codon after the point where the mutation occurred. During protein synthesis, incorrect amino acids would be inserted from the point where the frameshift mutation occurred on; the resulting protein would most probably be nonfunctional. For this reason, a frameshift mutation at the beginning of a gene is generally the most severe type of mutation.
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What are the consequences of having pyrimidine dimers in DNA?
a. These dimers distort the DNA structure and result in errors during DNA replication.
b. They create an apyrimidinic site
c. They prevent the transcription of the DNA into RNA.
d. They form an extra phosphodiester bond between them.
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a. These dimers distort the DNA structure and result in errors during DNA replication.
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Thymine dimers can be repaired by Photoreactivation Repair or Nucleotide Excision Repair.
T or F
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True. Both Photoreactivation Repair and Nucleotide Excision Repair will target UV-induced pyrimidine dimers in DNA.
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Which of the following statements regarding Nucleotide Excision Repair (NER) and Base Excision Repair (BER) is true?
a. Both NER and BER can be activated by exposure to visible light.
b. Both NER and BER involve the removal of one or more damaged bases by a nuclease.
c. Only NER involves the action of DNA ligase to seal nicks in the DNA backbone.
d. Both NER and BER involve the creation of an apyrimidinic (AP) site.
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b. Both NER and BER involve the removal of one or more damaged bases by a nuclease. This statement is true. In both NER and BER a nuclease will target damaged or distorted regions of DNA.
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Two different mutations are identified in a haploid strain of yeast:
The first prevents the synthesis of adenine by a nonsense mutation of the ade-1 gene. In this mutation, a base-pair substitution changes a tryptophan codon (UGG) to a stop codon (UGA).
The second affects one of several duplicate tRNA genes. This base-pair substitution mutation changes the anticodon sequence of a tRNATrp from 3'-ACC - 5' to 3'-ACU - 5'.
A. Do you consider the first mutation to be a forward mutation or a reversion?
-reversion or
-forward mutation
B.Do you consider the second mutation to be a forward mutation or a reversion?
a. forward mutation
b. second-site reversion (suppressor)
c. intragenic reversion
d. true reversion
C. Assuming there are no other mutations in the genome, will this double-mutant yeast strain be able to grow on minimal medium?
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A. Forward mutation
B. Second-site reversion (suppressor)
C. Yes
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Is heteroduplex DNA always an outcome of homologous recombination?
a. No, heteroduplex DNA is only created during homologous recombination when the homologs have different DNA sequences.
b. Yes, heteroduplex DNA is always created during homologous recombination.
c. Heteroduplex DNA formation and homologous recombination are not related.
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b. Yes, heteroduplex DNA is always created during homologous recombination.
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All compounds that have been found to be mutagenic in the Ames test are also carcinogenic.
T or F
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False. The Ames test is used as a preliminary screening tool. Not all compounds that give a positive Ames test are carcinogenic.
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Why are liver extracts used in the Ames test?
a. The bacteria require the nutrients present in the liver extract for growth.
b.Liver enzymes activate the bacterial enzymes.
c. Liver enzymes may activate some innocuous compounds, making them mutagenic.
d. A liver extract is necessary for the bacteria to produce histidine revertants.
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c. Liver enzymes may activate some innocuous compounds, making them mutagenic. Some compounds are innocuous until they are activated metabolically by liver enzymes.
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Which bacteria grow on the agar plate if the Ames test is positive?
a. his− auxotrophs
b. his+ auxotrophs
c. his− prototrophs
d. his+ prototrophs
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d. his+ prototrophs
The bacteria used in the Ames test to evaluate mutagenicity are his− auxotrophs. If the Ames test is positive, these bacteria have reverted back to wild type and are his+ prototrophs
