Errors in DNA replication

Question 1

What is DNA replication stress?

Answer 1

Inefficient replication

leads to replication fork slowing down, stopping or breaking

Question 2

What are the causes of DNA replication stress?

Answer 2

Defects in enzymes involved

Defects in DNA template strand

Defects in DNA repair pathways

Question 3

What are some examples of defects in DNA template strand?

Answer 3

Transcription occurring during DNA replication

Ribonucleotide included

DNA lesions

Question 4

What are some examples of DNA replication errors caused by defects in enzymes involved?

Answer 4

Slippage

Nucleotide misincorporation

Question 5

What happens in slippage?

Answer 5

Either the template DNA strand or the new DNA strand loops out

Question 6

What is the consequence of slippage?

Answer 6

New DNA strand is either missing a base

or has an extra base

Question 7

Which increases the risk of slippage?

Answer 7

Repeated base

Question 8

What is nucleotide misincorporation?

Answer 8

Incorrect base added to new DNA strand

not complementary

Question 9

What is responsible for removing mismatched bases?

Answer 9

3’ to 5’ exonuclease

Question 10

What causes nucleotide misincorporation?

Answer 10

Defects in 3’ to 5’ exonuclease

Question 11

What are the types of DNA strand breaks?

Answer 11

Single-strand breaks

Double-strand breaks

Question 12

What is responsible for repairing single-strand breaks?

Answer 12

Base-excision repair

Question 13

What causes single-strand breaks to persist?

Answer 13

Defect in base-excision repair

Question 14

What causes double-strand breaks? How?

Answer 14

Single-strand breaks followed by DNA replication

Replication fork reaches break
newly formed DNA molecule breaks off as double-strand

Question 15

What are the consequences of double-strand breaks in DNA?

Answer 15

Lead to translocation mutations
cell death
disease

Question 16

What do DNA mutations lead to?

Answer 16

Cancer

Question 17

What does cell growth inhibition lead to?

Answer 17

Ageing

Question 18

What is the cause of Huntington’s disease?

Answer 18

Increased number of trinucleotide CAG repeats in Huntington’s gene
produces a protein that gives neurodegeneration

Question 19

What causes the increased number of CAG repeats in Huntington’s disease?

Answer 19

Slippage

Question 20

How is Huntington’s disease inherited?

Answer 20

Autosomal dominant

Question 21

What does the number of CAG repeats in Huntington’s disease relate to?

Answer 21

The age of onset - more CAG repeats means earlier age of onset

Question 23

What is the multi-step cancer model?

Answer 23

Refers to how an accumulation of mutations is required to cause cancer

Question 24

What is the cause of Werner syndrome?

Answer 24

Mutations in the Werner gene
leads to defects in helicase, DNA replication
DNA damage

Question 24

What does the Werner gene code for?

Answer 24

Helicase enzyme involved in DNA replication

Question 24

How is Werner syndrome inherited?

Answer 24

Autosomal recessive

Question 26

What is the main symptom of Werner syndrome?

Answer 26

Premature ageing