You have made a collection of mutant fruit flies that aredefective in various as

Question

You have made a collection of mutant fruit flies that aredefective in various aspects of DNA repair. You test each mutantfor its hypersensitivity to three DNA-damaging agents: sunlight,methylnitrosourea (which cause alkation of guanosine),and nitrous acid (which causes deamination of cytosineand conversion to uracil which lead to a mutation and the necessity to repair during replication). each type of damage will lead to the activation of the three different repair pathways including base excision repair, nucleotide excision repair, and mismatch repair.The results are summarized in the figure below, where a“yes” indicates that the mutant is more sensitive (thereby defective in repair )than a normal fly and blanks indicate normal sensitivity.

...........................Sunlight| methyl nitrosurea| nitrous acid |
Dracula                           Yes |                                |                |
Faust |                                 |              Yes             |                 |
Mole |                            Yes |                                |                 |
Mr. Self-destruct |           Yes |              Yes             | Yes           |
Marguerite |                          l                                 |    Yes        |

A.

Which of the mutants is most likely to be defective in theDNA repair polymerase and why?

B.
for the remaining mutants not described in A identify which one of the three repair pathways listed above might be affected and a protein or enzyme that may not be functioning in that repair process that would lead to the inability of repairing that particular type of damage. make sure you think about where in the pathway the mutation may occur and describe the consequence

C.
The damage caused by sunlight can be repaired by a direct reversal of DNA damage and an indirect more complicated repair mechanism that involves several steps.compare and contrast the tow types of repair mechanisms that can fix this type of damaged DNA.

Explanation / Answer

a) Mutant which is more defective in repair is Mr. self destruct. It is showing sensitivity for all three mutagenic agents. Repair mechanism will become defective when the enzymes required for process are defective or when repair irreversible.

b) DNA glycosylase can recognize the apurinic site and remove its base. Ap endonuclease also plays role. When defect occurs in these enzymes it affects the repair pathways.

c) Damage caused by the sunlight is of two types. they are

- UV-B light causes crosslinking between adjacent cytosine and thymine bases creating pyrimidine dimers. This is called direct damage DNA.

- UV-A light creates mostly free radicals. The damage caused by free radicals is called indirect DNA damage.

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