Lecture 2 Flashcards
How does a typical bacteriophage work?
Bacteriophages insert their chromosome into their host cells in order to use all of the tools the cell has to replicate in order to produce more phage proteins which join together to produce the bacteriophage.
What was the fluctuation test and its outcome?
The fluctuation test had two models, if the adaptive response was correct approximately the same number of resistant mutants in each culture, but if random mutation and selection is the cause there would be large variation in mutant numbers. The outcome was that some cultures had no resistance, some had a small number, and a few had very large numbers (jackpot cultures, as bacteria hit the jackpot). This supports random mutation with selection. If many samples were taken the number of resistant colonies was more common. Overall data fit more with the random mutation model.
What were some limitations of the fluctuation experiment?
Limitations of the fluctuation experiment were: bacteria are rapidly killed so no time to adapt, can take some time for resistance mutations to give rise to resistence phenotype, extensive evidence however supports the random mutation model.
Why Aren’t there naturally high numbers of resistant mutants?
Resistance has a cost, they are less able to take up particular nutrients meaning the resistant mutants are less strong unless the bacteriophage is present.
What is a mutagen
Mutagens are an agent which is capable of increasing the mutation rate, they are associated with hereditary diseases and with cancer.
What are two possibilities for mutagen testing?
testing for mutagens could be to use laboratory animals (good laboratory model for humans, but cost to screen a large number of animals in order to ensure something is completely safe, how would you detect the mutations? and ethical concerns).
Another possibility would be using microorganisms (genes in microorganisms work the same way as for us, so mutagens for us and them should be the same, lots of microorganisms can be screened at once. Sensitive screens are available for detecting mutation occurence and there are no ethical issues).
How does the Ames test work?
The Ames test works by using strains of Salmonella typhimurium that have a mutation in a gene required to synthesise histidine. These will only grow with histidine, we can place these on a gel without this in the presence of a mutagen and see if they revert to normal (these bacteria are known as revertants). If the test compound increases revertant likelihood it is a mutagen.
Why do some strains work for the Ames test easily while others don’t?
Different strains may need different mutations, making it harder to become a revertant type.
What are some ways we can make the default Ames test better?
many chemicals that are not mutagenic to bacteria but are in animals, this is because they are converted into an active form in mammals by enzymes in the liver. We can add the active form instead of the original compound. We could also mutate a gene to make bacteria more susceptible, defective DNA repair gene or plasmid that enhances some mutagens.
