DNA Damage And Repair

Question 1

What happens if DNA is not repaired before the next replication cycle

Answer 1

The error becomes permanent and forms a mutation

Question 2

What happens to damaged DNA in germ cells if it is not repaired

Answer 2

The lesion will be transmitted to the offspring

Question 3

Where does DNA damage come from

Answer 3

Errors of DNA replication: despite its proofreading capabilities, DNA polymerase still has an error rate of 10^-10
Mutagens: chemical and environmental agents that cause changes in DNA molecules

Question 4

What is a tautomere

Answer 4

Isomers with slightly different chemical structures

Question 5

What are the different types of DNA damage

Answer 5

Single base alterations
Two base alterations
Chain breaks
Cross linkages

Question 6

What are some deaminating agents and how do they effect DNA

Answer 6

Nitrous acid or sodium bisulphate
Deaminating base pairs like adenine will form hypoxanthine
Hypoxanthine pairs with C instead of T

Question 7

What does the deamination of cytosine cause

Answer 7

Uracil
Binds with A instead of G

Question 8

What does the deamination of guanine do

Answer 8

Forms xanthine
Blocks DNA replication

Question 9

How does UV light cause DNA damage

Answer 9

It causes thymines to bind together (thymine dimerisation)

Question 10

What is an intercalating agent

Answer 10

A chemical agent that inserts itself between base pairs
Ethidium bromide

Question 11

What arc the different categories of mutations

Answer 11

Chromosomal mutations
Base pair mutations

Question 12

What are the different types of chromosomal mutations

Answer 12

Duplication
Inversion
Deletions
Insertion
Translocations

Question 13

What are the different base pair mutations

Answer 13

Insertion
Deletion substitution

Question 14

What is a base pair transition

Answer 14

When a purine mutates into another purine (A to G) / pyrimidine into another pyrimidine (T to C)

Question 15

What is a base pair transversion

Answer 15

When a purine mutates into a pyrimidine or vice versa (A to T or G to C)

Question 16

Why are point mutations dangerous

Answer 16

If the mutation forms a premature stop codon the protein will be truncated and likely stop functioning

Question 17

What are the different effects of point mutations

Answer 17

Silent: mutation has no effect since degenerate code means the same amino acid is generated
Missense: mutation cause a single amino acid to change in a sequence
Nonsense: mutation causes a premature stop codon to form
Frameshift mutation: insertion/deletion causes a shift in the reading frame likely altering a large portion of the peptide chain

Question 18

What are the different pathways of DNA repair

Answer 18

Direct repair
Repair by excision
Mismatch repair

Question 19

What happens during direct damage reversal (DDR) of DNA

Answer 19

An enzyme corrects a nucleotide alteration caused by mutagens

Question 20

What happens during the mismatch repair of DNA

Answer 20

DNA is corrected during DNA replication

Parent strand has the correct nucleotide, daughter strand contains mutation
The parent strand is distinguished from the daughter strand through hemimethylation (only the parent strand is methylated
MutS, MusL, MutH mediated the process
MutS bind to the mutation, MusL follows and MutH cuts out a large portion of DNA including the mismatch
DNA polymerase III and DNA ligase then repair

Question 21

What are the two types of excison repair in DNA

Answer 21

Base excision repair (BER): a single altered base is repaired
Nucleotide excision repair (NER): a chain of DNA containing the altered base is removed