Midterm #1 material Flashcards
What is an auxotroph
Unable to create all of its own nutrients from elemental substrates
What frequency does spontaneous mutants happen in?
10^-10 to 10^-9 for any phenotype
What makes mutants independent strains?
If one isolates a single mutant colony from each culture
What constitutes sibling mutant strains?
If one isolates more than one mutant colony from any single culture
What is selection?
Direct isolation
Why is selection beneficial?
You’re able to grow under restrictive conditions that select against the parental strain
In Screening, how do you transfer cells from mutant colonies?
Patching, replica plating to a variety of other media
What are the conditions for Screening?
Non-selective, permissive
What are the compounds required for biosynthesis that auxotrophic mutants cannot synthesize?
Amino acids, nucleotides, vitamins
What type of mutants are auxotrophs? What is the result of their characteristic?
- Biosynthetic/anabolic mutants
- Will fail to grow on minimal media regardless of carbon source
What are Catabolic mutants unable to do?
Break-down compounds supplied as a source of carbon/energy
What can you deduce from the appearance of auxotrophic phenotypes?
The mutagenesis was successful
How do you calculate transposition frequency?
Divide mutants/ml by recipients/ml
How do you increase mutation rate because the spontaneous mutation rate is too low?
Add mutagenic agent like chemical (EMS, NTG) or physical (UV)
How do you optimize probability of isolating desired mutants?
Following a chemical or physical mutagenesis procedure with an Enrichment step
What type of synthesis does penicillin-type antibiotics interfere with?
Peptidoglycan
What do Penicillin only kill?
Actively growing/dividing cells
What do Penicillin not kill?
Non-growing cells
What does Penicillin do to mutants under restrictive conditions?
Kill them
What do nutrients released from killed cells allow?
Mutants to grow under restrictive conditions and be killed by penicillin
Where can Penicillin enrichment only be done?
On liquid tubes not solid plates
What is Auxanography?
A way to identify nutrient requirement of auxotrophic
What is an auxotroph?
Strains that fail to grow because a nutrient they are unable to biosynthesize is missing from a medium
What are prototrophs?
Are able to biosynthesize all nutrients from C, N, P
What do mutations in any of the lac genes characteristically result in?
A lactose utilization phenotype
What is a mutation?
Change in the genetic code relative to the wild type or parental strain
What are examples of a mutation?
Base pair changes, insertions, deletions, rearrangements
What is a mutant?
An organism carrying a mutation(s)
What is Isogenic strains?
Has the same genetic background and
What are forward mutations?
Wild-type to mutant genotype
What are reversion mutations?
Mutant to wild-type genotype
What are Absolute Defective Mutations?
Same phenotype under all conditions and same phenotype in presence of other mutations
What are Conditional mutations?
Phenotype depends upon conditions or presence of other mutation
What are suppressor-sensitive mutations?
Mutations where the OG mutation puts a stop codon where a stop codon shouldn’t be
What are specific examples of nonsense mutations?
Amber (Am), Opal (Op), and Ochre (Oc)
What does Temperature Sensitive mean?
Mutant phenotype at restrictive temperature
What are frameshift mutations?
Insertion or deletion of a number of nucleotides that is not a multiple of 3 within the translated portion of gene
What are transitions?
Base change from a purine to another purine, or a pyrimidine to another pyrimidine
What is the make up of a purine?
A,G: Double ring
What is the make up of a pyrimidine?
T (U), C: single ring
What are transversions?
Base change from purine to pyrimidine
What is a silent mutations?
Mutated codon encodes the same amino acid as the wild-type codon
What are Neutral mutations?
Mutated codon encodes a different but functionally-similar amino acid
What is a missense mutation?
Mutated codon encodes a different amino acid
What is a nonsense mutation?
Mutated codon is a translational stop signal
How many start codons are there?
6
How many stop codons are there?
3
What are the examples of start codons?
AUG (methionine), GUG (Valine), UUG (Leucine)
What are the codons for the Ribosomal Binding site?
AGGA
What do wobble allows for?
tRNAs to insert an amino acid into a growing peptide chain
What is intragenic suppression?
Suppressor mutation occurring in the same gene as the first mutation
What is extragenic suppression?
Suppressor mutations within a different gene
