Wright Lecture 12: Mutagens and the Ames Test

Question 1

Mutagents

Answer 1

Agents that cause mutation

Question 2

Physical mutagens

Answer 2

Ionized radiation

Ultraviolet radiation

Question 3

Ionized radiation

Answer 3

Cosmic rays, X-rays, gamma rays
Creates free radicals: charges stable molecules, which can alter the structure of bases and break phosphodiester bonds in DNA

Question 4

Cosmic rays

Answer 4

From sun and other stars and unknown events in the universe
Subatomic particles
99% simple proteins (H and He nucleus)
1% solitary electrons

Question 5

Gamma rays

Answer 5

From radioactive decay
Produced by subatomic particles
Also arise in astrophysical processes

Question 6

X-rays

Answer 6

Emitted by electrons outside the atomic nucleus

Ie. X-ray tubes

Question 7

Free radicals

Answer 7

Reactive ions

Can alter the structure of bases and break phosphodiester bonds in DNA

Question 8

Ultraviolet radiation

Answer 8

From sunlight
Electromagnetic radiation of lower energy than ionizing radiation
Most common source is sun and other starts in intergalactic space
Can be generated by various types of lamps (mercury vapour lamps)
Causes pyrimidine dimers: covalent bonds
Sterilization of seminar floor hood by UV radiation

Question 9

Mercury vapour lamps

Answer 9

Make UV light

Question 10

Pyrimidine dimers

Answer 10

Covalent bonds between pyrimidine which causes kink in DNA

Question 11

Chemical mutagens

Answer 11

1. Base analogs
2. Base modifying agents
3. Intercalating agents

Question 12

Base analogs

Answer 12

Chemicals that appear similar to normal bases in DAN but causes incorrect base-pairing and introduce point mutations during DNA replication

Question 13

5-bromouracil

Answer 13

Nucleotide analog
Base looks similar to both thymine and cytosine
Normally base paris with adenine
When ionized, will base pair with guanine
Can cause transition mutations when it shifts to rare state during replication

Question 14

Base modifying agents

Answer 14

Chemicals that modify groups on the normal bases in DNA that result in incorrect base-pairing during DNA replication

Question 15

EMS

Answer 15

Alkylation of guanine to ethylguanine

GC to TA

Question 16

Nitrous Acid

Answer 16

Deamination of cytosine to uracil

CG to TA

Question 17

Hydroxylamine

Answer 17

Hydroxylation of cytosine to hydroxylaminocytosine

CG to TA

Question 18

Intercalating agents

Answer 18

Chemicals that distort the normal stacking of bases in DNA resulting in insertion or deletion of a single base-pair during DNA replication
Planar molecules that insert between adjacent bases in DNA: distort them by 0.68nm, the size of the base
First round of DNA replication, DNA polymerase randomly selects any nucleoside triphosphate opposite the intercalating agent
Causes frameshift mutation

Question 19

DNA repair enzymes

Answer 19

Correct damaged DNA

Question 20

Xeroderma pigmentosum

Answer 20

Autosomal recessive genetic disorder of DNA repair in which the ability to repair damage caused by UV light is deficient

Question 21

Ames test

Answer 21

Assay for chemical mutagenicity

Measuring reversion of His- Salmonella bacteria strain

Question 22

Measuring reversion of His- Salmonella bacteria strain

Answer 22

1. Inoculate plate of growth medium lacking histidine inoculated with salmonella that require histidine
2. Place test substance in well: diffuses outward, creating concentration gradient
3. Colonies of mutated Salmonella can grow on medium without histidine: mutagenic substance causes some organisms to mutate and grow on medium, nonmutagenic substance does not cause organisms to mutate, they do not grow on medium

Question 23

Inclusion of rat liver enzymes in Ames test

Answer 23

Rat liver enzymes mimic the chemical modification of potential mutagens in human body