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Chapter 4: Problem 9

Patients with the rare genetic disease xeroderma pigmentosum (XP) are very sensitive to light and are highly susceptible to skin cancers. The study of such patients has enhanced our knowledge of DNA repair because \(X P\) is caused by defective DNA repairnucleotide excision repair. (A variant, XP-V, is deficient in postreplication repair.) In nucleotide excision repair A. removal of the damaged bases occurs on only one strand of the DNA. B. only thymine dimers generated by UV light can be removed. C. the excision nuclease is an exonuclease. D. a single multifunctional enzyme carries out the repair process. E. only the damaged nucleotides are removed.

Short Answer

Expert verified
A: Removal of the damaged bases occurs on only one strand of the DNA. B: Only thymine dimers generated by UV light can be removed. C: The excision nuclease is an exonuclease. D: A single multifunctional enzyme carries out the repair process. E: Only the damaged nucleotides are removed. Answer: A, E

Step by step solution

01

Understand the options

Read and understand the given statements about nucleotide excision repair. 1. A: Removal of the damaged bases occurs on only one strand of the DNA. 2. B: Only thymine dimers generated by UV light can be removed. 3. C: The excision nuclease is an exonuclease. 4. D: A single multifunctional enzyme carries out the repair process. 5. E: Only the damaged nucleotides are removed.
02

Review nucleotide excision repair

Research nucleotide excision repair to determine the correct statement. Nucleotide excision repair (NER) is a DNA repair mechanism that removes damaged base pairs or nucleotides caused by various factors, such as UV light, chemical agents, and oxidative damage. The process involves several steps, including damage recognition, unwinding of the DNA, removal of the damaged nucleotides, and repair synthesis.
03

Analyze the options

Compare the given statements about nucleotide excision repair with the information about the process. 1. A: Removal of the damaged bases occurs on only one strand of the DNA. This statement is true. Nucleotide excision repair operates on a single DNA strand, utilizing the undamaged strand as a template for reconstructing the damaged section. 2. B: Only thymine dimers generated by UV light can be removed. This statement is false. NER is not limited to thymine dimers caused by UV light; it can also fix other types of DNA damage. 3. C: The excision nuclease is an exonuclease. This statement is false. The excision nuclease involved in the NER process is an endonuclease, not an exonuclease. 4. D: A single multifunctional enzyme carries out the repair process. This statement is false. The NER process involves multiple enzymes and proteins working together to fix the damaged DNA. 5. E: Only the damaged nucleotides are removed. This statement is true. NER specifically targets and removes the damaged nucleotides without affecting the undamaged DNA sequence.
04

Choose the correct statement

From the analysis above, options A and E are true statements regarding nucleotide excision repair. The correct choices are: - A: Removal of the damaged bases occurs on only one strand of the DNA. - E: Only the damaged nucleotides are removed.

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Most popular questions from this chapter

Retroviruses, like HIV which causes AIDS, have their genetic information in the form of RNA. Reverse transcriptase synthesizes a DNA copy of the viral genome. One drug used in treating AIDS is AZT, an analog of deoxythymidine, which has an azido group at the \(3^{\prime}\) position of the sugar. It can be phosphorylated and competes with dTTP for incorporation into the reverse transcript. Once incorporated, its presence terminates chain elongation. There is a window in which the effect is primarily on viral replication since AZT is much less effective at competing with dTTP for incorporation by cellular DNA polymerases because of the proofreading ability of DNA polymerases. Proofreading activity to maintain the fidelity of DNA synthesis A. occurs after the synthesis has been completed. B. is a function of \(3^{\prime}\) to \(5^{\prime}\) exonuclease activity intrinsic to or associated with DNA polymerases. C. requires the presence of an enzyme separate from the DNA polymerases. D. removes mismatched bases in the interior of the chain. E. does not occur in prokaryotes.

In the coding strand of DNA for the alpha gene of normal hemoglobin \((\mathrm{HbA}),\) the three bases that correspond to codon 142 of the mRNA are TAA and the alpha chain has 141 amino acids. In the coding strand of the gene for the alpha chain of Hemoglobin Constant Spring, the three bases are CAA and the chain contains 172 amino acids. Explain the mutation that has occurred.

Interfering with topoisomerases is one way of inhibiting DNA replication. Certain antibiotics target DNA gyrase (type II topoisomerase) of \(E\) coli inhibiting catalytic activity. Topoisomerase poisons prevent resealing of the phosphodiester bond, leaving covalent protein-DNA junctions. These compounds are used in rreating infections and as chemotherapeutic agentsAll of the following are correct about double-strand breaks in DNA except they A. can lead to loss of genetic information. B. are always involved in homologous recombination. C. are involved in nonhomologous recombination. D. are associated with a heterodimer (Ku) in mammals. E. can lead to mutations or improper regulation of gene expression.

Retroviruses, like HIV which causes AIDS, have their genetic information in the form of RNA. Reverse transcriptase synthesizes a DNA copy of the viral genome. One drug used in treating AIDS is AZT, an analog of deoxythymidine, which has an azido group at the \(3^{\prime}\) position of the sugar. It can be phosphorylated and competes with dTTP for incorporation into the reverse transcript. Once incorporated, its presence terminates chain elongation. The growing chain is terminated becausc A. the analog can not hydrogen bond to RNA. B. the presence of the AZT analog inhibits the proofreading ability of reverse transcriptase. C. AZT does not have a free \(3^{\prime}\) - \(\mathrm{OH}\). D. the analog causes distortion of the growing chain, inhibiting reverse transcriptase. E. \(d T T P\) can no longer be added to the growing chain.

Mismatch repair removes replication errors by excising incorrect bases. There is no DNA damage or modified bases present. How does the cell distinguish the newly synthesized strand and preserve the correct parental DNA strand?
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