Types of DNA damage and repair

Question 1

What is genetic instability in cancer cells?

Answer 1

Genetic instability refers to the increased accumulation of mutations and chromosomal abnormalities in cancer cells compared to normal cells.

Question 2

What are some factors contributing to genetic instability in cancer cells?

Answer 2

Mistakes during cell division and abnormalities in handling chromosomes contribute to genetic instability.

Question 3

What does aneuploidy mean in cancer cells?

Answer 3

Aneuploidy refers to the presence of an abnormal number of chromosomes, with either losses or extra copies of chromosomes.

Question 4

What are the characteristics of normal human cells in terms of chromosomes?

Answer 4

Normal human cells (except sperm and eggs) are diploid, possessing 23 pairs of chromosomes (46 chromosomes in total).

Question 5

What is the Philadelphia chromosome?

Answer 5

The Philadelphia chromosome is a chromosomal abnormality found in 90% of Chronic Myelogenous Leukemia (CML) patients, formed by a reciprocal exchange between chromosomes 9 and 22.

Question 6

How is the Philadelphia chromosome formed?

Answer 6

The Philadelphia chromosome is formed by DNA breakage near the ends of chromosomes 9 and 22, followed by reciprocal exchange of DNA between the two chromosomes.

Question 7

What is the result of the Philadelphia chromosome?

Answer 7

The result is the formation of an abnormal fusion protein called BCR-ABL, which drives uncontrolled cell proliferation.

Question 8

What is the role of apoptosis in cells with the Philadelphia chromosome?

Answer 8

Normally, cells with genetic defects like the Philadelphia chromosome would undergo apoptosis, but in cancer cells, defects in apoptosis pathways allow them to continue proliferating.

Question 9

What is translesion synthesis in DNA repair?

Answer 9

Translesion synthesis is the process where DNA polymerase synthesizes new DNA across damaged regions of the DNA template strand during replication.

Question 10

What are the steps of excision repair in DNA damage?

Answer 10

Excision repair involves: 1) DNA repair endonucleases recognize and excise damaged bases; 2) DNA polymerase fills in the gap using the undamaged strand; 3) DNA ligase seals the break.

Question 11

What is the difference between base excision repair and nucleotide excision repair?

Answer 11

Base excision repair corrects single damaged bases, while nucleotide excision repair removes larger defects such as thymine dimers.

Question 12

What enzyme is involved in base excision repair?

Answer 12

DNA glycosylases are responsible for recognizing and removing damaged bases in base excision repair.

Question 13

What does DNA glycosylase do in base excision repair?

Answer 13

DNA glycosylase recognizes a specific damaged base (e.g., deaminated bases) and removes it by cleaving the bond between the base and the DNA backbone.

Question 14

What happens after DNA glycosylase removes a damaged base?

Answer 14

After DNA glycosylase removes a damaged base, repair endonucleases cleave the DNA backbone, and DNA polymerase replaces the missing nucleotides.

Question 15

What is nucleotide excision repair (NER)?

Answer 15

NER is a repair system that recognizes large distortions in the DNA helix, such as thymine dimers, and excises the damaged region for repair.

Question 16

How does nucleotide excision repair (NER) work?

Answer 16

NER utilizes NER endonucleases to make two cuts around the damage, the DNA is unwound, and the gap is filled by DNA polymerase, followed by sealing by DNA ligase.

Question 17

What are common types of DNA damage?

Answer 17

Common types of DNA damage include depurination, deamination, and damage from mutagens like chemicals and radiation.

Question 18

What is depurination?

Answer 18

Depurination is the loss of adenine or guanine bases due to spontaneous hydrolysis of the bond linking the base to the DNA chain.

Question 19

What is deamination?

Answer 19

Deamination is the removal of the amino group from a base by hydrolysis, affecting base-pairing properties of the DNA bases.

Question 20

What is the role of mutagens in DNA damage?

Answer 20

Mutagens are agents that induce mutations by altering the DNA sequence, either by interacting directly with the DNA or by inducing chemical changes.

Question 21

What are alkylating agents?

Answer 21

Alkylating agents are chemicals that donate alkyl groups to DNA, causing mutations like transitions, transversions, and frameshifts.

Question 22

How do alkylating agents affect DNA?

Answer 22

Alkylating agents change the base-pairing properties of bases (e.g., GC to AT), potentially leading to errors during DNA repair processes.

Question 23

What is a base analog like 5-Bromouracil?

Answer 23

5-Bromouracil is a base analog similar to thymine that can be incorporated into DNA, increasing the frequency of mispairing during DNA replication.

Question 24

What is the effect of ultraviolet (UV) radiation on DNA?

Answer 24

UV radiation causes the formation of pyrimidine dimers between adjacent cytosine and thymine bases, distorting the DNA structure and causing replication errors.

Question 25

How does UV radiation cause mutations?

Answer 25

UV radiation triggers covalent bonds between pyrimidine bases, leading to pyrimidine dimers that distort the DNA helix, causing errors during DNA replication.

Question 26

What is ionizing radiation's effect on DNA?

Answer 26

Ionizing radiation removes electrons from biological molecules, generating highly reactive intermediates that cause DNA damage.

Question 27

What is the main characteristic of cancer cells' DNA repair mechanisms?

Answer 27

Cancer cells often have defective DNA repair mechanisms, allowing mutations and chromosomal abnormalities to accumulate, contributing to cancer progression.

Question 28

What is the function of DNA polymerase in excision repair?

Answer 28

In excision repair, DNA polymerase fills in the gap left by the excised damaged base, using the undamaged complementary strand as a template.

Question 29

How does the repair process of nucleotide excision repair (NER) differ from base excision repair?

Answer 29

NER repairs larger distortions in the DNA helix (such as thymine dimers), while base excision repair addresses smaller, single damaged bases.

Question 30

What are the consequences of disrupted apoptosis pathways in cancer cells?

Answer 30

Disrupted apoptosis pathways prevent the death of genetically damaged cells, allowing them to survive and continue proliferating despite mutations.

Question 31

How does translesion synthesis help during DNA replication?

Answer 31

Translesion synthesis allows specialized DNA polymerases to replicate across damaged regions of the DNA, bypassing lesions that would otherwise halt replication.

Question 32

What is the significance of mutations in the p53 gene in cancer?

Answer 32

Mutations in the p53 gene disrupt the main internal pathway for triggering apoptosis, allowing cancer cells to evade programmed cell death and continue dividing.