Mod 8- Causes Of DNA Mutation & DNA Repair

Question 1

What is a mutation?

Answer 1

An alteration in the nucleotide sequence of a DNA molecule.

Question 2

What are spontaneous mutations?

Answer 2

Mutations that result from errors in DNA replication.

Question 3

What causes strand-slippage during DNA replication?

Answer 3

Regions of DNA containing many copies of small repeated sequences.

This is when it loops out to add or remove a nucleotide (causing frame shift)

Question 4

What is base tautomerism?

Answer 4

A phenomenon where a DNA polymerase is tricked by isomers with slightly different chemical structures.

Question 5

What is an important base analog used in mutation studies?

Answer 5

5-bromouracil (5bU).

Question 6

What does 5-bromouracil (5bU) mimic?

Answer 6

Thymine.

Question 7

What is the consequence of enol-5bU pairing incorrectly during replication?

Answer 7

It pairs with G instead of A.

Question 8

What are mutagens?

Answer 8

Chemical or environmental agents (radiation/ UV light) that cause changes in DNA molecules.

Question 9

What is the effect of deaminating agents on adenine?

Answer 9

Deamination of adenine gives hypoxanthine, which pairs with C not T.

Question 10

What does deamination of cytosine produce?

Answer 10

Uracil, which pairs with A not G.

Question 11

What are alkylating agents?

Answer 11

Agents that add alkyl groups to nucleotides.

Question 12

Name an example of an alkylating agent.

Answer 12

Ethylmethane sulphonate (EMS).

Causes transition mutation

Question 13

What type of mutation do intercalating agents cause?

Answer 13

Insertion mutations.

Question 14

What is an example of an intercalating agent?

Answer 14

Ethidium bromide.

Question 15

What type of DNA damage is caused by ultraviolet radiation?

Answer 15

Causes bases to interact with themselves

Base dimerization- bases connect to each other

Photoproducts.

Question 16

What is an AP site?

Answer 16

Apurinic, apyrimidinic site resulting from the detachment of bases.

Question 17

How often does depurination or depyrimidination occur?

Answer 17

About 1000 times a day.

Question 18

True or False: Thymine can be deaminated.

Answer 18

False.

Question 19

Fill in the blank: Deamination of guanine gives _______.

Answer 19

xanthine.

This blocks DNA replication as it can’t base pair with anything

Question 20

What effect does heat have on DNA?

Answer 20

Causes detachment of bases, leading to an AP site.

Question 21

What is the primary importance of DNA repair?

Answer 21

Preserving the composition and coding potential of the genome

Question 22

What is direct repair in the context of DNA mutations?

Answer 22

An enzyme corrects a nucleotide alteration caused by a mutagen

Question 23

Which enzyme in E. coli can remove alkyl groups from nucleotides?

Answer 23

ADA enzyme

Removes alkyl groups attached to position 4 of T and position 6 of G

Question 24

What is the function of the MGMT enzyme in humans?

Answer 24

Removes alkyl groups from position 6 of G

Question 25

What type of DNA damage can be repaired by DNA photolyase in E. coli?

Answer 25

Base dimers formed by UV radiation

Question 26

What is the nucleotide excision repair system?

Answer 26

Damaged nucleotide is removed and the gap is filled by DNA synthesis

Question 27

What are the two types of excision repair?

Answer 27

* Base excision repair- a single altered base is removed * Nucleotide excision repair- a longer piece of DNA containing the altered bases is removed

Question 28

How does base excision repair happen in E. coli?

Answer 28

Begins with removal of the damaged base by a DNA glycosylase enzyme Heat gives rise to an AP site AP site is then filled

Question 29

What does AP stand for in the context of DNA damage?

Answer 29

Apurinic, apyrimidinic site

Question 30

What enzyme carries out nucleotide excision repair in E. coli?

Answer 30

UvrABC endonuclease The region containing the damaged nucleotide is excised and resynthesised

Question 31

What distinguishes the parent strand from the daughter strand during mismatch repair in E. coli?

Answer 31

The parent strand is methylated

Question 32

Which enzymes recognize mismatches in E. coli?

Answer 32

* MutH * MutS The mismatch is excised and the DNA is resynthesised

Question 33

How does mismatch repair in humans differ from that in E. coli?

Answer 33

Humans do not involve methylation and use MutS-like proteins for mismatch recognition

Question 34

What is the role of telomeres in nonhomologous end joining?

Answer 34

Mark the natural ends of chromosomes

Question 35

What happens during nonhomologous end joining in humans?

Answer 35

DNA ligase joins the two ends together

Question 36

What are the 2 ways in which mutagens can cause mutations?

Answer 36

1. Base analogs = mutagenic chemicals that look like bases and are incorporated into the DNA 2. Direct structural change = DNA is physically changed by environmental factor

Question 37

What are deaminating agents?

Answer 37

Remove the NH2 group Change the structures of some nucleotides

Question 38

What are intercalating agents?

Answer 38

Inserted between base pairs

Question 39

What is mismatch repair?

Answer 39

Corrects errors in DNA replication Parent strand contains correct nucleotide Daughter strand contains the mismatch