Question

Question 23 and 24) To control a microbial population on the surface of your sample, you exposed it to UV light. 23) UV light damages the microbial DNA by forming_. A) highly reactive radicals B) double strand breaks C) acetylation D) purine dimers E) thymine dimers 24) This damage (the answer for question 23) kills bacterial cells by A) inhibiting translation by ribosomes B) inhibiting DNA replication and transcription C) inhibiting peptidoglycan synthesis D) blocking glycolysis E) preventing the use of oxygen as the final electron acceptor

Answer 1

23 E

24 B

Direct DNA damage can occur when DNA directly absorbs a UVB photon, or for numerous other reasons. UVB light causes thymine base pairs next to each other in genetic sequences to bond together into pyrimidine dimers, a disruption in the strand, which reproductive enzymes cannot copy.

Other names for the "direct DNA damage" are :

Thymine dimers

Pyrimidine dimers

Cyclobutane Pyrimidine dimers

UV-endonuclease-sensitive-sites (ESS)

Ultraviolet (UV) light kills cells by damaging their DNA. The light initiates a reaction between two molecules of thymine, one of the bases that make up DNA. The resulting thymine dimer is very stable.

The longer the exposure to UV light, the more thymine dimers are formed in the DNA and the greater the risk of an incorrect repair or a "missed" dimer. If cellular processes are disrupted because of an incorrect repair or remaining damage, the cell cannot carry out its normal functions.

The pyrimidine dimers cause a kink in the DNA backbone, halting transcription and protein synthesis.