Wright 12 - Mutagens and the Ames Test Flashcards
What type of mutagens are ionizing radiations (eg. cosmic or x-rays) and ultraviolet radiations examples of?
Physical mutagens
What type of mutagens are base analogs, base modifying agents and intercalating agents examples of?
Chemical Mutagens
What are cosmic rays composed of?
99% simple protons and 1% solitary electrons
Where do gamma rays come from?
Originate form radioactive decay, produced by sub-atomic particles, also arise in astrophysical processes.
What are x-rays emitted by?
Electrons outside the nucleus. Human source is form x-ray tubes.
What does ionizing radiation do?
Creates free radicals, which can alter the structure of bases and break phosphodiester bonds in the DNA
What has a higher ionizing energy? UV or ionizing radiation?
ionizing
What does UV radiation due to DNA?
Causes pyrimidine dimers to form, this is where two pyrimidines bind together. This creates a kink in the DNA. The most common pyrimidine dimer is a thymine dimer.
What are base analogs?
Chemicals that appear similar to the normal bases in DNA, but causes incorrect base-pairing and introduce point mutations during DNA replication.
What are base modifying agents?
Chemicals that modify groups on the normal bases in DNA that result in incorrect base pairing during DNA replication
What are intercalating agents?
Chemicals that distort the normal stacking of bases in DNA resulting in insertion or deletion of a single base-pair during DNA replication
What is 5-bromouracil?
A nucleotide analog that acts similar to the pyrimidines (specifically thymine and cytosine)
Normally base pairs with adenine, but when ionized it wil base pair with guanine.
When undegoing DNA replication, 5-bromouracil switches between rare and normal state, and therefore introduces incorrect base pairing and point mutation sequence.
What might base modifying agents do to a sequence with G-C in it?
Convert the G-C to A-T
How do intercalating agents distort normal stacking of bases and cause insertion or deletions of single base pairs during DNA replication?
They are planar molecules that inser themselves between adjacent bases in DNA. Examples are proflavin and acridine orange.
These distort distances between adjacent bases by .68 nm, the size of a base.
During DNA replication the polymerase randomly selects any nucleoside triphosphate opposite the intercalating agent. Then in a second round of DNA replication there is normal base pairing, the result is a frameshift owing to insertion of one base pair.
What are the steps of the Ames test?
- A plate of -His growth medium is inoculated with Salmonella that require histidine.
- Place test substance in a well (the substance will diffuse out and create a concentration gradient)
- Incubate
- Mutagenic substance causes some organisms to mutate and grow on medium
A plate with no growth has a nonmutagenic substance
