Mutagens

Question 1

Name two forms of mutations.

Answer 1

Spontaneous and induced

Question 2

What causes induced mutations?

Answer 2

Mutagens.

Question 3

Mention three common types of mutagens.

Answer 3

• physical
• chemical
• induced

Question 4

List chemical mutagens.

Answer 4

• deaminating agents
• alkylating agents
• base analogues
• bulky addition products
• intercalating agents

Question 5

What do deaminating agents cause?

Answer 5

The removal of amino groups from nitrogenous based.

Question 6

Give an example of the work of a deaminating agent.

Answer 6

Removing the Amino group from cytosine leaving it as uracil.

Question 7

State a change in base pairing this may cause starting from CG.

Answer 7

CG-UA-AT

Question 8

What is the name of the substance that delaminates cytosine to form uracil?

Answer 8

Nitrous acid

Question 9

State what alkylating agents do.

Answer 9

These mutagens add alkyl groups to nitrogenous bases.

Question 10

Give examples of alkyl groups.

Answer 10

CH3, CH2CH3

Question 11

What may the addition of alkyl groups lead to?

Answer 11

Deletion of such bases, especially the purines adenine and guanine.
Or mispairing of bases.

Question 12

Name a disease deaminating agents age linked to.

Answer 12

Gastric cancer

Question 13

Give examples of alkylating agents.

Answer 13

Dimethylsulphate
Diethylsulphate
Ethylmethane sulphate

Question 14

Give on illustration of an alkylation taking place.

Answer 14

Ethyl methane sulphate generates ethylation at the O-4 position of thymine. The modified thymine will mispair with guanine leading to TA-GC transition.

Question 15

Name some conditions alkylating agents are linked to.

Answer 15

Bladder, bronchial and blood cancer.

Question 16

What are base analogues?

Answer 16

Mutagens that look like normal bases thus confusing the DNA replication system.

Question 17

Give 2 examples of base analogues. And state what they are analogues of.

Answer 17

5- bromouracil an analogue of thymine

2-amino purine an analogue of adenine

Question 18

Give an example of the effect of a base analogue.

Answer 18

5-bromouracil, an analogue of thymine, will pair with guanine. When affected DNA replicates, it produces the change TA-5bromouracil/guanine-GC

Question 19

What are bulky addition products??

Answer 19

Large molecules able to covalently bond to purines leading to deletion of such purines from the affected DNA.

Question 20

Name one bulk addition mutagen and where it is found.

Answer 20

Aflatoxin B1 a carcinogen found in seed crops such as groundnuts and maize.

Question 21

Name what the previous bulk addition mutagen is linked to. (2)

Answer 21

Liver cancer

Hepatitis B

Question 22

The attachment of a bulky addition product, such as Aflatoxin B1 will disturb things in what way.

Answer 22

Deletion of affected purine, in this case guanine leaving an apurinic site.

Question 23

What is an apurinic site?

Answer 23

Location in DNA that is neither a purine or pyrimidine. Caused spontaneously or due to damage.

Question 24

What does the repair system usually do and what change does it lead to.

Answer 24

Repair system usually inserts guanine in site of deletion.

Leads to change CG-C*-CA-TA

Question 25

What’s an intercalating agent?

Answer 25

Molecules that have three rings which mimic base pairs.

Question 26

How will intercalating agents affect DNA?

Answer 26

Insert themselves between base pairs in the affected DNA double helix, causing frame shift mutations.

Question 27

Give three examples of intercalating agents.

Answer 27

- proflavin (antiseptic antibacterial and urinary) - acridine orange (dye used in lab detection of mycobacterium) - ethidium bromide (fluorescent dye)

Question 28

Mention the two most important physical mutagens.

Answer 28

- UV radiations | - ionization radiations

Question 29

What do UV radiations do??

Answer 29

Generates the pyrimidine (thymine) dimers which cause cancer e.g melanoma and keratosis.

Question 30

List three examples of ionization radiations.

Answer 30

- X rays - Gamma rays - neutrons - alpha rays

Question 31

What do ionization radiations lead to? What do they cause

Answer 31

Generation of free radicals which cause breaks in DNA

Question 32

What’s the ultimate result of ionization radiations?

Answer 32

Results in deletions and other types of mutations in affected DNA

Question 33

Liste three examples of biological mutagens.

Answer 33

Viruses Transposable elements Some bacteria

Question 34

Explain how mutagenic viruses work.

Answer 34

When a viral infection is acquired, the virus attatches to a cell and transfers genetic material into the cell thus altering the original gene causing mutation.

Question 35

Give one example of a DNA viral mutagen and an RNA virus. | What disease can they cause?

Answer 35

DNA-hepatitis B RNA-hepatitis C Liver cancer

Question 36

Give three more examples of mutagenic viruses.

Answer 36

- human herpes virus - SV40 - human papilloma virus

Question 37

Transposable elements also cause mutations. Explain how they disturb functions.

Answer 37

Segment of DNA able to move from one position to another in the same chromosome or from one chromosome to another. When inserted into a new position on chromosomal DNA it disrupts function of genes.

Question 38

What does mutagenic bacteria do?

Answer 38

Causes inflammation during which oxidative species are produced. Causes DNA damage by reducing efficiency of DNA repair systems thereby increasing mutations.

Question 39

Give one example of mutagenic bacteria.

Answer 39

Helicobacter pylori