Lab 6: Effects of UVR on Yeast Cells

Question 1

primary effect of UVR

Answer 1

causes covalent linkages between thiamine bases in yeast dna, resulting in dimers that prevent the DNA from replicating. Yeast may also try and repair the DNA but, it is faulty, resulting in mutations and lethal effects

Question 2

What is the formula for percent survival?

Answer 2

% survival= [(average colony count on UVR)/average colony count on control] x 100

Question 3

What is the relationship between survival of yeast as done of UVR increases?

Answer 3

exponential relationship between cell death and increasing dose. The higher the intensity or the higher the dose, the more damage the yeast will sustain.

Question 4

what enzyme is used during photoreactivation? What does it do to the yeast cells?

Answer 4

photolyase enzyme. binds to dimers and splits the thiamine dimers when excited by white light.

Question 5

How is PR system effected by UVR dose?

Answer 5

the PR system is more effective when the dose of radiation is smaller.

Question 6

Why does PR not repair all the damage caused by UV radiation?

Answer 6

there are other forms of DNA damage such as dna-protein crosslinks, ring cleavage, etc.

there is a limited amount of photolyase enzyme, it cannot repair all the damage sustained by UVR

Question 7

What are the other forms of DNA repair other than PR?

Answer 7

1) nucleotide excision repair- cuts out DNA lesions a few base pairs long
2) base excision repair- cuts out mutated/wrongly paired DNA by cleaving its bond with the sugar base, creating a gap
3) base bypass- entire mutation damaged area is skipped over during replication