02.12 - DNA Mutagenesis, Repair, and Relevant Diseases

Question 1

It refers to any permanent heritable change in the DNA base sequence of an organism.

Answer 1

Mutation

Question 2

Which of the following process makes use of DNA recombination?

a. DNA repair
b. Immunoglobulin rearrangement
c. Crossing-over during meiosis
d. Integration of viral DNA

Answer 2

All of the above makes use of DNA recombination.

Question 3

A replacement of a single base with another single base nucleotide is called ______________.

Answer 3

Point mutation

Question 4

A certain mutagen caused the mutation in the short DNA sequence 5’-GGACTCG-3’. The new sequence reads 5’-GGGCTCG-3’. What type of point mutation occurred?

Answer 4

Transition

Question 5

A mutation from 5’-ACCGTTA-3’ to 5’-ACCTTTA-3’ is what type of point mutation?

Answer 5

Transversion

Question 6

When a point mutation results in the same amino acid, it is called a ____________.

Answer 6

Silent mutation

Question 7

When a point mutation results in a new codon that codes for a different amino acid, a _____________ has occurred.

Answer 7

Missense mutation

Question 8

A missense mutation that resulted in the replacement of aspartic acid with glumatic acid, which are both hydrophilic in nature, is said to be _____________.

Answer 8

Conservative

Question 9

When a missense mutation results in a different amino acid with different properties, it is said to be ____________.

Answer 9

Non-conservative

Question 10

When a point mutation results in a premature stop codon, a ___________ has occurred.

Answer 10

Nonsense mutation

Question 11

____________________ results after the deletion or addition of a number of bases not divisible by three.

Answer 11

Frameshift mutation

Question 12

_______________ occurs when large areas of chromosomes are lost during unequal crossover in meiosis.

Answer 12

Large segment deletion

Question 13

DNA repair occurs during what phase of the cell cycle?

a. G1
b. G2
c. S
d. M

Answer 13

b. G2 (after DNA replication has occurred after the S phase)

Question 14

Arrange the steps of DNA repair in order.

I - Endonuclease nicks the mismatched strand and mismatched base is removed
II - DNA polymerase I and DNA ligase completes repair
III - Mismatched strands are identified

a. I-II-III
b. I-III-II
c. III-II-I
d. III-I-II

Answer 14

d. III-I-II

Question 15

Also known as the Lynch syndrome, this early onset hereditary disease is characterised by the familial clustering of cancers at several sites.

Answer 15

Hereditary non-polyposis colorectal cancer (HNPCC)

Question 16

Which of the following is the cause of HNPCC?

a. Microsatellite instability
b. Mismatch repair deficiency
c. Thymine dimerization
d. A and B

Answer 16

d. A and B

Question 17

Name two genetic pathways that can lead to cancer.

Answer 17

Activation of oncogenic pathways

Inactivation of tumor suppressor genes

Question 18

What is the cause of xeroderma pigmentosum?

a. Failure to repair mismatched DNA strand
b. Inactivation of timor suppressor genes in skin cells
c. Large segment deletion
d. Failure to replicate DNA due to thymine dimerization

Answer 18

d. Failure to replicate DNA due to thymine dimerization

Question 19

Arrange the steps of abnormal base replacement in order:

I - Formation of apyrimidinic or apurinic site (AP site)
II - DNA polymerase and DNA ligase complete the repair
III - Deoxyribose-phosphate lyase removes the single empty sugar-phosphate residue
IV - Abnormal nitrogenous base is removed by cleaving N-glycosidic bond
V - AP-endonucleases make a nick at the 5’ site of the AP site

a. IV-I-V-III-II
b. IV-V-I-III-II
c. V-IV-I-II-III
d. V-I-III-IV-II

Answer 19

a. IV-I-V-III-II

Question 20

In DNA repair of abnormal bases, what enzyme hydrolytically cleaves the abnormal nitrogenous base from the deoxyribose-phosphate backbone?

Answer 20

Glycosylases (Tip: Remember that it cleaves the N-glycosidic bond between the nitrogenous base and sugar)