Condition Mutations Flashcards
What are non-conditional mutations?
Display mutant phenotype under all conditions, regardless of environment or temperature or medium
What is a null mutation?
Complete knockout
What is a leaky phenotype?
Partial mutant phenotype
What are conditional mutations?
Only displays the mutant phenotype under certain environmental conditions
What are permissive conditions?
Conditions that allow the mutants to survive and grow and behave like WT cells
What are restrictive conditons?
Conditions that show the mutant phenotype
Why are conditional mutations important for studying genetics in bacteria and phages?
Only way to study essential genes, since its the only way to study a lethal mutation
What are 3 commonly used conditional mutations?
Auxotrophs
Temperature sensitive
Suppressor sensitive
What is an auxotroph?
The mutant lacks the ability to synthesize a compound required for growth
What are permissive conditions for an auxotroph?
Rich medium or supplemented minimal medium with the thing the cell can’t make
What are restrictive conditions for an auxotroph?
Minimal media
What happens at different temperatures for a non-lethal temp sensitive mutant?
Shows a different phenotype like a colour change at high temps vs at low temps, but the cell/virus doesn’t die
What are the permissive conditions for a non-lethal temp sensitive mutant?
Low temps
What are the restrictive conditions for a non-lethal temp sensitive mutant?
High temps
What is a conditional lethal temp sensitive mutant?
Contains a temp sensitive mutation in an essential gene. Cells die in restrictive conditions
What are the permissive conditions for a conditional lethal temp sensitive mutant?
Low temps
What are the restrictive conditions for a conditional lethal temp sensitive mutant?
High temps - they die
Why is the higher temp the restrictive condition for a temp sensitive mutant?
These mutations cause the protein to be destabilized at higher temps
How would you look for temp sensitive mutations in a particular pathway?
- Mutagenize the cells
- Plate under permissive conditions so all cells, mutant and WT survive
- Replica plate onto restrictive conditions
- Compare the plates and look for something that looks different or doesn’t grow in the restrictive conditions
How does the FluMist vaccine work?
The virus is live, but has a temp sensitive mutation that stops it from replicating at high temps. Your nose is a low enough temperature that the virus can replicate enough to stimulate an immune response, but if it gets in your lungs it becomes inactive so you can’t get sick. Because the virus is live and not injected it can get into other people’s noses and they create antibodies against it too
What are suppressor sensitive mutations?
Informational suppressor mutation
What are the permissive conditions for suppressor sensitive mutations?
A strain of bacteria carrying the suppressor. The WT phenotype shows
What are the restrictive conditions for suppressor sensitive mutations?
A WT strain of bacteria with no suppressor. The mutant phenotype will show
What are nonsense suppressors?
Original mutation is a nonsense mutation, and the suppressor is in the anticodon of the tRNA that causes the stop codon to be misread as an AA
Do nonsense suppressors tend to put the right AA in place of the nonsense mutation?
Not usually
What is the problem with nonsense suppressors?
Causes a bunch of other stop codons to be misread, which causes stop codons where the protein is actually supposed to stop to be missed, and a bunch of proteins end up longer than normal
Do nonsense suppressor strains grow very well?
No, they grow slowly even on rich media because a bunch of proteins are being slightly messed up
Does a single nonsense suppressor work for all nonsense mutations?
No, depends on which stop codon it is. A suppressor will only fix one stop codon
What are the names for the 3 stop codons?
Amber, ochre, opal
