Biology II: Chapter 15 HW
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 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.
UvrD is nonfuctional A mutation has occurred that has made UvrD nonfunctional. 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.
Insert the correct terms in the following statements about oncogenes, tumor suppressor, and mutations involved in cancer.
The insertion of a virus into the promoter of a gene could result in increased expression of the gene, resulting in cancer. A chromosomal translocation can cause fusion of the two genes together, resulting in formation of a chimeric oncogene. A change in the number of copies of a gene can cause too much protein to be made. A missense mutation can alter the structure of a protein (but not the total number of amino acids) so that it now has abnormally high activity. Many cells that have accumulated mutations are eliminated by cell death. If a cell accumulates DNA damage during mitosis, the cell cycle can pause at a checkpoint.
Cancer cells often are missing chromosomes. How could loss of chromosomes result in cancer?
The missing chromosomes could have contained tumor-suppressor genes.
Which of the following would occur from a mutation in the gene's promoter region?
The rate of transcription may increase or decrease.
Formation of thymine dimers 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
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?
A young girl was born with a patch of soft fur that ran from the base of her neck to her tailbone. She did not display any other symptoms of disease, and results of her karyotype seemed normal. No one on either her mother or father's side of the family had ever been born with this oddity. Her concerned mother's side asked a doctor if her daughter would have children that were similarly furry. 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.
After a tautomeric shift in adenine
adenine bonds with cytosine
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.
UV light damages DNA by causing
covalent bonds to form between thymine and nucleotides next to each other on the same DNA strand.
UV light and other ionizing radiations damage DNA molecules by... 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
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
Type of bonds affected by thymine dimers What kind of bond do thymine dimers weaken?
hydrogen bonds.
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
A mutation in a gene in the fruit fly Drosophila was found to affect eye color. The protein affected was found to be completely normal in its molecular weight and amino acid sequence, although much less of the protein is made in mutant flies. 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
The mutations observed by the Lederbergs were
spontaneous
In light repair
the covalent bonds between the thymine dimers are broken.
Mutation in the DNA The following sequence of DNA is part of the normal, wild-type gene. 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.
The nucleic acid sequence in mRNA is determined by
the nucleotide sequence in DNA
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
Sequencing Cancer Steps Sequence the following steps in the development of cancer in an individual with xeroderma pigmentosum (XP)
1. Mutation in DNA repair enzyme gene 2. Exposure to UV light 3. Mutation of tumor-suppressor gene 4. Benign growth 5. Malignant growth 6. Metastasis
Which of the following could not result from mutations?
A fish in a stream dies from a poison that blocks cellular respiration
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
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
The following are examples of changes in cell behavior. Determine whether they could result in cancer (unregulated cell growth) or not.
Could cause cancer: 1. loss of an essential checkpoint protein 2. loss of the tumor suppressor p53 Would likely not cause cancer: 1. blocking of DNA polymerase 2. slight increase in apoptosis 3. increase in accuracy of DNA replication 4. activation of p53
The following are examples of the activities of some DNA repair mechanisms. Sort the examples into the appropriate category. [Note: 8-oxoG is a damaged G base.]
DIRECT PAIR 1. Removal of an alkyl group from a G NUCLEOTIDE EXCISION REPAIR 1. Removal of a damaged A base 2. Recognition of a TT dimer 3. removal of 8-oxoG METHYL-DURECTED MISMATCH REPAIR 1.Recognition of a mismatched G-T base pair shortly after replication
What characteristic of DNA makes nucleotides 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.
Repair of dimers What enzyme is responsive for repairing thymine dimers using the energy of light?
DNA photolyase
Which of the following synthesizes the new DNA strand?
DNA polymerase
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.
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
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
Which mutation would allow the cell to divide when it should not and could possible lead to cancer?
None of these will lead to cell proliferation
Deletion in CCR5 CCR5 is a cell surface receptor protein of white blood cells that attracts them to a specific tissue and organs to elicit an immune responce. It is also the receptor to which R5 strains of HIV bind to and enter T cells. Between 5-14% of people from Northern European descent possess an allele known as CCR5-Δ32. 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.
Mechanism of thymine dimer repair Which of the following statements about the repair mechanism involving photolyase is TRUE?
Photolyase is oxidized and the damaged DNA is reduced.
For each of the following examples of mutations in the codon sequences of a gene, predict the likely effect on the function of polypeptide gene product (no effect on function, weak effect, or strong effect). You will need to consult the genetic code in Table 12.1. Note that the codons shown in the examples correspond to the coding strand of the DNA -- recall how the sequence of the coding strand relates to the mRNA.
STRONG EFFECT 1. CGA --> TGA near beginning of gene 2. GAG --> GTG change in important part of coding region 3. insertion of one base (+1) shortly after codon NO EFFECT 1. AAG --> AAA in middle of gene 2. TGA --> TAA at end of coding region 3. change of a C to a G before the ATG WEAK EFFECT 1. change of codon of one acidic amino acid into another acidic amino acid
Mutation in the DNA - Insertion The following sequence of DNA is part of the normal, wild-type gene. 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 a premature stop codon and a truncated protein.
A carcinogen is a chemical or treatment that
causes mutations that increases the likelihood of developing cancer
A nucleotide deletion in DNA replication
causes the amino acids inserted after the deletion to be incorrect
A mutation that causes a change in a single nucleotide in DNA
changes the corresponding nucleotide in mRNA, resulting in a different codon.
