Ch. 14 Biology
A chromosome has undergone a translocation mutation that has completely deleted its centromere region, preventing association with spindle fibers. What will be the fate of this cell?
The cell will not pass this M phase checkpoint because its chromosomes will not all associate with spindle fibers.
A cell has a mutation such that UvrA is permanently attached to UvrB. What effect might this have on nucleotide excision repair (NER)?
The cell would be able to recognize damaged regions of the double helix, but it would be unable cut the DNA in the appropriate region in preparation for removing the damaged sequence.
A mutation has occurred that prevents UvrA and UvrB from forming a complex. What result will this have on damaged DNA?
The damaged DNA will not be recognized.
A mutation has occurred that has made UvrD non-functional. What result will this have on damaged DNA?
The damaged segment of DNA will be recognized and cut, but it will not be separated from the healthy strand.
5' ATG CGG GTA GTT AGC CGA TAG 3' A deletion occurs during DNA replication, causing the guanine shown in red to be removed from the nucleotide strand. What effect is this most likely to have on the final protein
The deletion of the G will cause a frame shift, resulting in a premature stop codon and a truncated protein.
Which of the following mutations might result in the formation of an oncogene?
The duplication of a proto-oncogene, so that it occurs several times in a single chromosome
Evaluate the following statements and determine which is the most likely explanation for how the methylation of a guanine might induce mutations in the DNA?
The guanine will not properly hydrogen bond with cytosine across the double helix
Cancer cells often are missing chromosomes. How could loss of chromosomes result in cancer?
The missing chromosomes could have contained tumor-suppressor genes.
The devastated parents consult you as a genetic advisor on the likelihood that a future pregnancy would end similarly. What advice do you give this couple?
The mutation was probably a germ-line mutation that only affected a single egg or sperm, so they should try to have more children.
Many genes that are associated with cancer can become mutated due to slipped-strand mispairing. These genes include p53, retinoblastoma, Wilms tumor, and the breast cancer gene BRCA1. What characteristic would you expect to find in all these genes?
They all have repetitive sequences in the gene.
The growth factors illustrated in the system are positive regulatory growth factors. Why are they considered 'positive' growth factors?
They increase the rate of cell proliferation.
How does ultraviolet light result in the formation of thymine dimers?
Ultraviolet light provides the energy for covalent bond formation between two thymines.
Which protein cuts the damaged DNA strand?
UvrC
Which protein has a helicase function?
UvrD
An actively dividing cell is missing an entire chromosome. How might this lead to cancer?
Various tumor suppressor genes may have been deleted from the genome, so cell proliferation occurs regardless of the damaged genome.
Which of the following statements about oncogenes is FALSE?
When oncogenes are silenced, the cell cycle may be able to proceed even when it should not.
Slipped-strand mispairing may cause deletions resulting in
a frameshift mutation.
After a tautomeric shift in adenine
adenine bonds with cytosine.
UV light damages DNA by causing
covalent bonds to form between thymine nucleotides next to each other on the same DNA strand.
How does UV light and other ionizing radiation damage DNA molecules?
creating thymine dimers between adjacent thymines in the DNA chain.
The proteins ________ work together to free the transcription factor that is bound by the retinoblastoma protein.
cyclin and cyclin dependent kinase
If the protein retinoblastoma is _____ it can bind to and _____ the Myc protein
dephosphorylated; inactive
Mutated forms of the Rb protein
do not bind to E2F thereby promoting uncontrolled cell division.
In a tautomeric shift
hydrogen atoms move to form a nucleotide base with altered bonding properties.
What kind of bond do thymine dimers weaken?
hydrogen bonds.
Slipped-strand mispairing requires that a DNA sequence be present
in multiple copies on both homologous chromosomes
The nucleic acid sequence in mRNA is determined by
nucleotide sequence in DNA.
A reasonable explanation for the change in levels of protein is that the mutation
occurs in the promoter of the gene, within several hundred base pairs of the start of transcription.
The protein ________ checks for damaged DNA, thereby acting as a "quality control" for the cell.
p53
During slipped-strand mispairing, homologous chromosomes.
pair up with each other, but out of register.
A tumor suppressor gene normally functions to
prevent development of cancer
The Ras protein normally regulates cell growth. A mutation that occurs in the gene encoding Ras can cause Ras to become overactive, which results in cancer. This means that Ras is an example of a/an
proto-oncogene.
The mutations observed by the Lederbergs were
spontaneous
When a tautomeric shift occurs, the resulting nulceotide is a(n) __________ of the nucleotide prior to the shift.
structural isomer
In light repair
the covalent bonds between the thymine dimers are broken.
If a frameshift mutation causes a stop codon to be inserted into the DNA sequence,
the resulting protein will be too short and non-functional.
A gene encodes a protein that normally functions in promoting the programmed cell death of blood cells that have accumulated damage to DNA. A mutation in this gene can result in leukemia (cancer of the blood). This gene is an example of a/an
tumor-suppressor gene.
Oncogenes and tumor-suppressor genes have the shared property that
when either type of gene is mutated, cancer can result.
Which of the following mutations might result in the formation of an oncogene?
A cell has a damaged segment of DNA, however p53 proteins are mutated so that they cannot bind to the DNA and activate transcription factors that would stop the cell cycle.
Which of the following could not result from mutations?
A fish in a stream dies from a poison that blocks cellular respiration
Which of the following mutagens might increase the incidence of slipped-strand mispairing?
A mutagen that stabilized single-stranded DNA
Which mutation would allow the cell to pass the G1 checkpoint when it should not?
A mutation in Rb, preventing it from associating with E2F.
Mutations in the protein retinoblastoma (Rb) are often associated with cancer in the eye. What mutation might lead to cancer?
A mutation that prevents Rb from interacting with myc
What result is characteristic of slipped-strand mispairing mutation?
A protein that, starting at the point of the deletion, has incorrect amino acids and is of abnormal length.
The doctor told her that while he couldn't be 100% certain, he suspected that this characteristic was the result of
A somatic mutation that occurred in the developing embryo, but probably wouldn't affect the daughter's egg cells
Which of the following mechanisms might result in reduced levels of functional p53 in the cell?
A virus, such as HPV, inactivates p53
Which of the following is an example of a mutation?
An A-T base pair in a gene is changed to a G-C base pair
Why is breast cancer a very deadly form of cancer?
Because breasts contain numerous blood vessels and lymph nodes, so breast cancer can easily metastasize and spread throughout the body.
Why are people afflicted with xeroderma pigmentosa likely to develop skin cancer?
Because they are born with a mutation in their DNA repair system and they cannot repair DNA that is mutated by UV radiation.
Which of the following is not a reason why cells need to be able to repair damaged DNA?
Cells need to change base pairs to be able to express different types of proteins
Cancer progression can result from mechanisms other than mutation (change in the DNA sequence). Which of the following is not an example of such a mechanism?
Chromosomes could be lost during meiosis.
The gene that codes for a certain caspase enzyme has a point mutation so that it can no longer degrade certain proteins. This will result in
Conversion of a proto-oncogene to an oncogene
What characteristic of DNA makes nucleotide excision repair (NER) mechanisms possible?
DNA is a double helix so once a damaged region is recognized, it can be removed and synthesized based on the undamaged opposite strand
What enzyme is responsible for repairing thymine dimers using the energy of light?
DNA photolyase
Which of the following synthesizes the new DNA strand?
DNA polymerase
You want to test the mutagenicity of a certain chemical that you suspect causes changes to DNA molecules. You have not been able to locate the Salmonella typhimurium strain that requires histidine in order to grow. What might you be able to use instead?
E. coli bacteria that contain a point mutation in a gene that encodes an enzyme required in the arginine biosynthetic pathway.
Which of the following statements about repair of thymine dimers is TRUE?
Excision repair can be used to repair thymine dimers as well as other types of damaged DNA.
Which of the following statements regarding the repair of thymine dimers is TRUE?
Excision repair of thymine dimers is possible because there are two strands of DNA.
A cell that is in an environmentally that has an abnormally low pH will NOT pass which checkpoint?
G1
The cell cycle is regulated by checkpoints during the _______ phases.
G1, G2, and M
DNA repair enzymes will be highly active during what phase of the cell cycle?
G2
The success of DNA replication is assessed during the ______ phase.
G2
When a tautomeric shift occurs, which of the following is TRUE?
In the new DNA strand, a purine is always replaced by a purine, and a pyrimidine is always replaced by a pyrimidine.
Which of the following is not a mechanism by which viruses could cause cancer?
Infection by a virus could cause the immune system to kill the infected cells by apoptosis.
How does myc become active.
It dissociates from Rb
Below are the results of the Ames test for mutagenicity for three different mutagens, X, Y, and Z. Which of the following statements is FALSE?
Mutagen Y is the least mutagenic.
You are examining a gene that normally has the sequence ACGATTTGGCGC But in the mutant fruit fly you have produced, you see the sequence ATGATTTGGTGT What likely caused this mutation?
Mutations induced by HNO2
What mutation would allow the cell to divide when it should not and could possibly lead to cancer?
None of these will lead to cell proliferation.
In this allele, a 32 base pair section of the gene has been deleted. What phenotype would you predict for people carrying the CCR5-Δ32 allele?
People with CCR5-Δ32 will likely have impaired immune function, but will have resistance to HIV infection.
Which of the following statements about the repair mechanism involving photlyase is TRUE?
Photolyase is oxidized and the damaged DNA is reduced.
In the Ames test for mutagenicity, why was rat liver extract included in the control sample?
Rat liver extract contains enzymes that may be necessary for certain mutagens to work. Since it must be added to the experimental sample, it is also added to the control sample.
5' ATG CGG GTA GTT AGC CGA TAG 3' An insertion occurs during DNA replication, causing an additional GUANINE to be inserted into the nucleotide strand after the GUANINE shown in red. What effect will this have on the final protein?
The addition of the G will cause a frame shift, resulting in the loss of the normal stop codon and an abnormally long protein with an altered amino acid sequence.
A eukaryotic cell that receives a "go-ahead" signal at the G1 checkpoint of the cell cycle will
complete the cycle and divide.
A carcinogen is a chemical or treatment that
causes mutations that can affect gene activity.
A nucleotide deletion in DNA replication
causes the amino acids inserted after the deletion to be incorrect.
Growth factor receptors are typically found in the
cell membrane
A mutation that causes a change in a single nucleotide in DNA
changes the corresponding nucleotide in mRNA, resulting in a different codon.
