Week 2: Dna Damage And Repair

Question 1

What is a mutation?

Answer 1

Any change from the normal DNA sequence

Includes deletions, insertions, and substitutions.

Question 2

What are the three types of mutations?

Answer 2

• Deletions
• Insertions
• Substitutions

Question 3

What are transitions in mutations?

Answer 3

• Purine to purine (e.g. A to G)
• Pyrimidine to pyrimidine (e.g. C to T)

Question 4

What are transversions in mutations?

Answer 4

Purine to pyrimidine (or vice versa)

Question 5

What are the consequences of high numbers of mutations in the germ line?

Answer 5

They would destroy the species.

Question 6

What are the consequences of high numbers of mutations in somatic cells?

Answer 6

They would destroy the individual organism.

Question 7

What are exogenous sources of DNA damage?

Answer 7

• Ionising radiation (e.g. X-rays)
• UV light (sunlight)
• Chemicals (e.g. hydrocarbons in cigarette smoke)

Question 8

What type of DNA damage is caused by UV light?

Answer 8

Thymine cross-linking (thymine dimers)

Question 9

What are endogenous sources of DNA damage?

Answer 9

• DNA replication errors
• Hydrolysis
• Spontaneous depurination
• Spontaneous deamination
• Oxidation

Question 10

What is depurination?

Answer 10

The removal of guanine or adenine from DNA.

Question 11

What is deamination?

Answer 11

The conversion of cytosine to uracil.

Question 12

What are reactive oxygen species (ROS)?

Answer 12

Normal metabolic by-products of respiration that can cause DNA damage.

Question 13

What is the most frequent spontaneous chemical reaction creating serious DNA damage?

Answer 13

Depurination and deamination.

Question 14

What are the consequences of DNA damage?

Answer 14

• Cell death
• Functional decline of tissues
• Cancer
• Developmental deficiencies
• Embryonic lethality

Question 15

What is the proofreading activity of DNA polymerase?

Answer 15

A mechanism that helps correct errors during DNA replication.

Question 16

What does Base Excision Repair (BER) do?

Answer 16

Removes single damaged bases.

Question 17

What is Nucleotide Excision Repair (NER)?

Answer 17

Removes thymine dimers and large chemical adducts.

Question 18

What is Mismatch Repair (MMR)?

Answer 18

Removes mismatched base pairs and insertion/deletion loops.

Question 19

What is Non-homologous end joining (NHEJ)?

Answer 19

Repairs double-strand breaks (DSB) by joining broken ends regardless of sequence.

Question 20

What is Homologous recombination repair (HR)?

Answer 20

Repairs double-strand breaks (DSB) using a sister chromatid.

Question 21

What are the common themes of DNA repair?

Answer 21

• Detect the damage
• Remove the damage
• Resynthesis/Repair
• Regulation

Question 22

True or False: Failure to repair DNA damage can result in cell death.

Answer 22

True.

Question 23

What genetic disorders are associated with defective repair mechanisms?

Answer 23

• Xeroderma pigmentosa (UV sensitivity)
• Hereditary nonpolyposis colon cancer (HNPCC)
• Bloom syndrome (premature aging)

Question 24

What role does BRCA1 play in DNA repair?

Answer 24

Involved in both checkpoint arrest and double-stranded DNA repair.

Question 25

Fill in the blank: The process of removing methyl groups from DNA is performed by _______.

Answer 25

O6-methylguanine-DNA methyltransferase.

Question 26

How often does depurination occur in nucleated human cells?

Answer 26

Each nucleated human cell loses ~5,000 DNA purines per day.

Question 27

What is oxidative damage in DNA?

Answer 27

Damage caused by reactive oxygen species attacking purine and pyrimidine rings.