Question

Answer all the listed questions. Provided reasoning for correct answer. Provide reasoning for incorrect answers as well.

19) Which of the following is not generally associated with oxidative DNA damage?

a) build-up of wastes such as reactive oxygen species

b) Cross-linked complementary strands

c) Intrastrand crosslinks

d) Free radicals

--------------------------------------

20) Normal error correction of misincorporated bases carried out by DNA polymerase is called__.

a) Proofreading

b) Homologous recombination

c) Nucleotide excision

d) base excision

Answer 1

Ans.(19).Cross-linked complimentary strands.is not the characteristics of the Oxidative DNA damage .

(A).Build up of wastes such as reactive oxygen species. DNA Oxidative damage from reactive oxygen species is the common type of damage that is faced by cells .It leads to many different mutations and problems in DNA.

(C).Interastrand crosslinks.

Oxidative DNA damage has been reported to cause a variety of lesions go DNA such as intrastrand crosslink which in turn results in double strand breaks.

(D). Free Radicals.

These are produced in cells by cellular metabolism and by exogenous agents.they react with biomolecules and their target is DNA,that is referred as Oxidative DNA damage.

Ans.(20).a.Proofreading

Explanations.Normal error correction of missincorporated bases is carried out by DNA polymerase by the process of proofreading. By this process,the DNA polymerase reads the newly added bases before adding the next one,so a correction can be made.If an incorrect base is incorpirited then the enzyme makes a cut at the phosphodiester Bond and release the wrong nucleotide.

B.Homologous recombination is a type of genetic recombination in which the sequence of a nucleotide are exchange between two similar molecules of DNA.

(C). Nucleotide Excision repair is important Excision mechanisms that removed the damage of DNA that occurs by ultraviolet radiations.It repairs the bulky helix destroying lesions .

(D).Base Excision repair is a cellular process that repairs damaged DNA throughout the cell cycle.It is important mainly fo small,non helix destroying base lesions from the genome.