Chapter 25: Q21CP (page 915)
What are the functions of DNA phtolyases and alkytransfarses?
The enzymes Photolyase and alkytranferases are the phylogenetically old enzymes which is present and junctional in many species.
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The base analog 5-bromouracil (5BU),
which sterically resembles thymine, more readily undergoes tautomerization from its keto form to its enol form than does thymine. 5BU can be incorporated into newly synthesized DNA when it pairs with adenine on the template strand. However, the enol form of 5BU pairs with guanine rather than adenine. (a) Draw the 5BU · G base pair. (b) What type of mutation results?
Approximately how many Okazaki fragments are synthesized in the replication of the E. colichromosome?
Certain sites in the E. coli chromosome are known as hot spots because they have unusually high rates of point mutations. Many of these sites contain a 5-methylcytosine residue. Explain the existence of such hot spots
In E. coli, all newly synthesized DNA appears to be fragmented (an observation that could be interpreted to mean that the leading strand as well as the lagging strand is synthesized discontinuously). However, inmutants that are defective in uracil–DNA glycosylase, only about half the newly synthesized DNA is fragmented. Explain.
A certain mutant DNA polymerase is error-prone, tending to incorporate C opposite a template A. When such a DNA polymerase replicates a segment of DNA containing an A · T base pair, what will be the DNA composition in the daughter cells after (a) one and (b) two rounds of cell division? Assume that DNA repair does not occur.
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