DNA Damage

Question 1

DNA damage can be either

Answer 1

structural or point mutation

Question 2

When DNA damage occurs

Answer 2

the DNA repair system recognizes and corrects the damage

Question 3

If the damage is not repaired

Answer 3

it will create a mutation during DNA replication.

Question 4

What are the factors that cause replication-mediated mutagenesis ?

Answer 4

Endogenous factors

Exogenous factor

Question 5

Endogenous

Answer 5

Spontaneous

Induced

Question 6

Spontaneous

Answer 6

1. DNA polymerase proof reading failure mediated errors
2. Depurination mediated errors
3. Deamination mediated errors
4. Tautomers mediated errors

Question 7

Induced

Answer 7

Natural metabolism that releases reactive oxygen species

Question 8

Exogenous factor

Answer 8

UV irradiation mediated DNA damage

Question 9

Proof reading in leading and lagging strand

Answer 9

3’-5’ Exonuclease activity of DNA polymerase III

Question 10

RNA primer gap replaced by DNA fragment

Answer 10

3-5’ Exonuclease activity of DNA polymerase I

Question 11

When DNA polymerase fails to correct error, the system that recognizes and corrects the errors

Answer 11

Mismatch repair system

Question 12

the mismatch repair system fails to correct the error

Answer 12

During replication, the uncorrected mismatched nucleotides will create a permanent mutation in the genome

Question 13

Depurination

Answer 13

refers to the loss of purines (guanine or adenine) from a nucleotide

Question 14

Depurination occurs through

Answer 14

A spontaneous hydrolysis reaction

Question 15

How does depurination induce mutation ?

Answer 15

DNA polymerase skips the depurinated site during replication and create a deletion mutation.

Question 16

Deamination

Answer 16

refers to the loss of amino group (NH2).

It occurs due to spontaneous hydrolysis

Question 17

Deamination of :

Cytosine ➡️

Answer 17

Uracil

Question 18

Deamination of :

Adenine ➡️

Answer 18

Hypo-xanthine

Question 19

Deamination of :

Guanine ➡️

Answer 19

xanthine

Question 20

Deamination of :

5-methylcytosine

Answer 20

Thymine

Question 21

Loss of amino group from methyl cytosine creates Thymine. If repair system fails to repair the thymine

Answer 21

it creates a transition mutation (cytosine to thymine) during replication.

Question 22

Pyrimidine (C) to Pyrimidine (T) change is called

Answer 22

transition mutation

Question 23

Tautomers

Answer 23

are nucleotide isomers that spontaneously interconvert by a chemical reaction called tautomerization.

Question 24

Thymine and guanine bases shifting a hydrogen atom

Answer 24

From keto to enol

Question 25

Adenine and Cytosine bases, | – shifting a hydrogen atom

Answer 25

From amino to imino

Question 26

Tautomers creates a

Answer 26

transition mutation

Question 27

ROS species primarily base pairs with

Answer 27

guanine

Question 28

ROS converts guanine to

Answer 28

8-hydroxyl guanosine (8-OHdG)

Question 29

Purine (G) to Pyrimidine (T) change is called

Answer 29

transversion mutation

Question 30

most common type of DNA damage caused by UV irradiation

Answer 30

Is thymine dimer

Question 31

Thymine dimer

Answer 31

UV light attacks the two adjacent thymine bases and cross links between carbon atoms 5 & 6 positions of two adjacent thymine bases.

Question 32

This causes the bending of the DNA and disrupts the bonding of these two thymine

Answer 32

with their complimentary adenine nucleotides.

Question 33

Thymine dimers is also an example for

Answer 33

the structural damage of DNA

Question 34

What are the different repair mechanisms available to correct the DNA damage ?

Answer 34

1. Base Excision Repair 2. Nucleotide Excision Repair 3. Mismatch Repair

Question 35

Base excision repair corrects the altered base derived

Answer 35

from oxidative deamination in which amino group is converted into keto group.

Question 36

Removal of uracil which was created by the spontaneous deamination of cytosine in the DNA is by

Answer 36

The enzyme uracil DNA glycolase

Question 37

The backbone near the defect is cut by an

Answer 37

Endonuclease

Question 38

The defect is filled by the action of 9

Answer 38

DNA polymerase 1

Question 39

The strand is rejoins by

Answer 39

ligase

Question 40

Removal of the thymine dimers that was induced by ultra violet light is by

Answer 40

Nucleotide excision repair

Question 41

Recognition and cleavage of the damaged strand

Answer 41

UV specific endonuclease (uvrABC excinuclease)

Question 42

Correction of mis-incorporated bases that arise during DNA replication by

Answer 42

Mismatch repair (mmr)

Question 43

MutS recognize the mismatch and recruits

Answer 43

MutL

Question 44

MutL then recruites

Answer 44

MutH → endonuclease

Question 45

MutH

Answer 45

Cuts the DNA strand flanking the mismatch

Question 46

chews all the nucleotides in the small DNA fragment (flanking mismatch site).

Answer 46

Exonuclease 1

Question 47

Missense mutation

Answer 47

is a point mutation (A to C) in which a single nucleotide change results in a codon that codes for a different amino acid.

Question 48

Histidine

Answer 48

CAT

Question 49

Proline

Answer 49

CCT

Question 50

Nonsense mutation

Answer 50

is a point mutation in a sequence of DNA that results in creation of a premature stop codon.

Question 51

Glycine

Answer 51

CAG

Question 52

Stop codon

Answer 52

TAG

Question 53

Nonsense mutation

Answer 53

Short and incomplete protein product

Question 54

which a deletion or insertion of nucleotides in a DNA sequence shifts the reading frame of the coding sequence that results in a completely different translation of protein sequence from the original protein.

Answer 54

Frame shift mutation is point mutation

Question 55

Defects in Nucleotide Excision Repair

Answer 55

Xeroderma pigmentosum (XP)

Question 56

Rare autosomal recessive disease

Answer 56

Xeroderma pigmentosum

Question 57

Xeroderma pigmentosum patients

Answer 57

Are photosensitive and susceptible to skin cancer

Question 58

Xeroderma pigmentosum is due to

Answer 58

Defect in the nucleotide excision repair of the damaged DNA

Question 59

Defects in Base excision repair

Answer 59

Ataxia-telangiectasia

Question 60

degenerative motor condition caused by failure to repair oxidative DNA damage in the cerebellum.

Answer 60

Ataxia-telangiectasia

Question 61

It is a rare inherited disorder due to mutation in Ataxia-telangiectasia mutated (ATM) gene which is a part of base excision repair system

Answer 61

Ataxia-telangiectasia

Question 62

It also affects the immune system, and other body systems.

Answer 62

Ataxia-telangiectasia

Question 63

Defects in Mismatch repair system

Answer 63

Hereditary Nonpolyposis Colon Cancer

Question 64

Hereditary Nonpolyposis Colon Cancer

Answer 64

mutations in the genes encoding for mismatch repair system, which fails to correct the repair