Genetics of Bacteria mutagenic treatment question

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Discussion Overview

The discussion revolves around the effectiveness of various mutagenic treatments in creating mutations in non-replicating bacterial cells. Participants explore the mechanisms of different mutagens and their implications for mutagenesis experiments.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Exploratory

Main Points Raised

  • One participant suggests that all listed treatments primarily cause mismatches, questioning their effectiveness in non-replicating cells.
  • Another participant emphasizes the need to consider how mutagenesis experiments are conducted, noting that mutations are typically detected after cells are allowed to grow post-treatment.
  • It is mentioned that most treatments will damage bacterial DNA regardless of whether the cells are dividing, except for one treatment that does not cause changes in non-replicating cells.
  • Discussion includes the role of DNA polymerases in bypassing damage caused by UV exposure, indicating that some treatments may still lead to mutations during replication.
  • Some participants express uncertainty about the simplicity of the problem, with one suggesting that oxidation may not occur in non-growing cells.
  • A later reply prompts participants to consider the chemical alterations caused by each mutagen to purified DNA, shifting focus from cellular context to chemical interactions.

Areas of Agreement / Disagreement

Participants do not reach a consensus on which mutagenic treatment is least effective in non-replicating cells, with multiple competing views and uncertainties remaining throughout the discussion.

Contextual Notes

Participants highlight the complexity of mutagenesis and the need to consider experimental conditions, such as the state of cell growth and the mechanisms of DNA damage and repair.

outxbreak
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Q: Which of the following mutagenic treatments would be least effective in creating a mutation in non-replicating cells? Explain your choice.
a. Treatment with a deaminating agent like nitrous acid
b. Treatment with an alkylating agent like MMS
c. Treatment by exposure to UV
d. Exposure to excess superoxide radicals
e. Treatment with a base analog like 2-aminopurine





I said:
a. Treatment with a deaminating agent like nitrous acid
Deamination causes base pair changes so mutants arise after replication

b. Treatment with an alkylating agent like MMS
Alkylating bases mispair.. problem for replicating cells

c. Treatment by exposure to UV

d. UV causes pyrimidine dimmers. DNA pol cannot replicate through a dimer so lethal to cells if not repaired

e. Exposure to excess superoxide radicals
8-oxoG mispairs with adenine

f. Treatment with a base analog like 2-aminopurine
potent mutagen that causes G:T and T:G misicorporations, i.e., it is also a transition mutagen.


So the problem is that all of them really just cause mismatches.. which means none would be effective for non-replicating cells? What am I missing? :/
 
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outxbreak said:
Q: Which of the following mutagenic treatments would be least effective in creating a mutation in non-replicating cells? Explain your choice.
a. Treatment with a deaminating agent like nitrous acid
b. Treatment with an alkylating agent like MMS
c. Treatment by exposure to UV
d. Exposure to excess superoxide radicals
e. Treatment with a base analog like 2-aminopurine


I said:
a. Treatment with a deaminating agent like nitrous acid
Deamination causes base pair changes so mutants arise after replication

b. Treatment with an alkylating agent like MMS
Alkylating bases mispair.. problem for replicating cells

c. Treatment by exposure to UV

d. UV causes pyrimidine dimmers. DNA pol cannot replicate through a dimer so lethal to cells if not repaired

e. Exposure to excess superoxide radicals
8-oxoG mispairs with adenine

f. Treatment with a base analog like 2-aminopurine
potent mutagen that causes G:T and T:G misicorporations, i.e., it is also a transition mutagen.So the problem is that all of them really just cause mismatches.. which means none would be effective for non-replicating cells? What am I missing? :/

I think you are missing thinking about how a mutagenesis experiment would normally be done.

At the moment the experiment is done the cells, in this case we are told, are not growing. But afterwards the mutants are not detected by looking at each cell, one by one, and if so how would the mutation be detected? We have to assume that after the treatment the mutagenic agent is removed and then the cells are grown without and probably plated out on a selective medium (or just plated out immediately after the mutagenic treatment and then they grow from single cells to visible colonies) to detect the mutants.

You probably have an account of such experiments in your textbook.

I think you should look again at each case with that in mind.
 
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All but one of those treatments will damage the DNA of the bacteria whether the cell is dividing or not. Only one of those will not cause changes to the DNA when the cells are not replicating, but will cause copying errors during DNA replication.
 
I'm guessing that is the UV damage? Thanks!
 
Although DNA polymerase III (the polymerase responsible for most DNA replication in bacteria) cannot synthesize past the pyrimidine dimers, bacteria contain other DNA polymerases (e.g. DNA pol IV and DNA pol V) that can perform translesion synthesis and bypass thymine dimers.
 
outxbreak said:
I'm guessing that is the UV damage? Thanks!

Think again - the answer is more simple and self-evident and no need to guess, at least if you know what these various agents do.
 
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We seem to have lost the OP. This is a very simple question. There are thes various and complicated mechanisms to avoid or make good the damage, but in one of the cases there wouldn't be any damage in non-growing cells.
 
I don't really know the answer. It makes since that UV could be repaired by other enzymes.. sorry I don't see how it's so "simple".
 
outxbreak said:
I don't really know the answer. It makes since that UV could be repaired by other enzymes.. sorry I don't see how it's so "simple".

Forget about repair. Repair does not come into this. How does the DNA get damaged in the first place? Go through each case. How does growth, replication, come into it?
 
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  • #10
I read my book again and the only thing I can imagine is that oxidation does not happen to the non-growing cells.. :/
 
  • #11
Imagine you have purified DNA in a test tube. Expose that DNA to each of the five mutagens from the question. Which of these mutagens will chemically alter the DNA in the test tube (here it's useful to think of the chemistry of how each mutagen alters the DNA), and which ones will not?
 
  • #12
I have given up on this problem!

Thanks anyways
 
  • #13
The ethos of this site is we do not do the homework for the students. Problems may involve a series of stages and our help often consists in splitting the problem up into stages, which I and Ygggdrasil have tried to do, and then asking back about the first step, etc.. Then without seeing an attempt by you to e.g. answer Ygggdrasil's last question we also must abandon it.
 
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  • #14
Yeah I would have deleted this board but Idk how.
 

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