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The base-pairing atoms of thymine are not directly involved in the cyclobutane ring of a pyrimidine dimer, formed by UV irradiation. Why does a pyrimidine dimer stall the replicative DNA polymerase?
Name three of the common ways in which DNA lesions are incurred.What is required for these DNA lesions to result in a mutation?
In the experiment described in Problem 4, some of the untreated serine auxotrophs were able to grow on a medium lacking serine. Why?
In an experiment using S. typhimurium histidine auxotrophs, the cells are grown on a thin layer of agar with nutrient medium that lacks histidine. The culture (~109 cells) produces ~13 colonies over a two-day incubation period at 37°C. (a) How did these colonies arise in the absence of histidine? (b) When the experiment is repeated in the presence of 0.4 μg of 2-aminoanthracene, the number of colonies produced over two days exceeds 10,000. What does this indicate about 2-aminoanthracene? c) what can you surmise about its carcinogenicy
Describe the most critical difference between global nucleotide excision repair and transcription-coupled repair.
What do base excision repair and repair of an abasic site have in common? How do they differ?
Many eukaryotes have a DNA glycosylase that specifically removes T residues from DNA, but only when they are paired with G. There is no comparable enzyme that removes the G residues from G-T mismatches.Why is it useful for a cell to always repair a G-T mismatch to G≡C rather than to A=T?
Many bacteria, including E. coli, are capable of growing under both anaerobic and aerobic conditions. Some mutations are introduced into an E. coli strain that inactivate several enzymes involved in DNA repair.The mutant strain grows normally when kept in an incubator with a 100% nitrogen gas atmosphere. However, the strain dies when exposed to a normal laboratory atmosphere. Why?
In an E. coli cell, DNA polymerase III makes a rare error and inserts a G opposite an A residue at a position 850 bp away from the nearest GATC sequence. The mismatch is accurately repaired by the mismatch repair system. How many phosphodiester bonds derived from deoxynucleotides (dNTPs) are expended in this repair process? ATPs are also used in this process. Which enzymes consume the ATP?
If an oxidative lesion occurs spontaneously in a single-stranded DNA fragment generated on the lagging strand during replication, it is not readily repaired by nucleotide excision repair or base excision repair.Explain why.
O6-Methylguanine lesions are repaired directly by transfer of the methyl group to O6-methylguanine methyltransferase. A very high level of metabolic energy is invested in this simple methyl transfer reaction.Describe this energy investment.
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