Chemical Mutagens Flashcards
Which base does 5-bromouracil substitute?
Thymine
Which tautomeric forms can 5-bromouracil exist in?
Both keto and enol.
HNO2 deaminates adenine to form which base, and which base does this new base pair with?
A -> hypoxanthine, which pairs to C.
HNO2 deaminates cytosine to form which base, and which base does this new base pair with?
C -> U, which pairs to A.
In terms of mutagenesis, what is the problem with deaminating C -> U?
Uracil is detected by repair systems are removed.
What base does NH2OH modify, and what is this modified base called?
C -> N 4-hydroxycytosine
What base does N 4-hydroxycytosine behave like?
Thymine
NTG, EES, and EMS are examples of what agents?
Alkylating Agents
What are the effects of alkylation on bases?
Changes in H-bonding patterns, mispairing, depurination.
What effect do intercalating agents have on DNA?
They insert between DNA base adjacently.
What effect on a reading frame does intercalation have?
Frameshift mutation (+1, sometimes +2)
What causes the frameshift mutation?
DNA excision.
What effect does UV light have on DNA?
It causes thymine dimer formation.
What wavelength is the UV light?
260nm
What is photoreactivation?
A visible light induced system that cleaves thymine dimers.
What is Dark Repair?
A thymine dimer excision system.
What are the Dark Repair gene products?
Uvr A,B,C
Why is Dark Repair non error-prone?
The thymine-dimer is excised, and the strand is reformed from the template strand.
When is SOS Repair activated? (In relation to thymine dimer repair)
When Dark Repair leaves residual DNA lesions.
RecA catalyses the clevage of what protein?
LexA
In the context of SOS repair, what is the function of LexA?
It represses SOS Repair.
recA is switched on by the SOS Repair system. What mechanism does this activate?
A positive feedback mechanism - the clevage of LexA.
What is the sfi gene?
Cell division inhibitor.
What are the umuC,D genes?
Inducible error-prone repair genes.
