Module 6 Flashcards
what are mutations and mutants?
Describe isolation of mutants (screening vs selection)
Compare spontaneous vs induced mutations
Spont.
-Occur without external intervention
-Most result from occasional erros by DNA polymerase during replication
Induced:
-caused environmentally or deliberately
-can result from exposure to natural radiation or chemical that chemically modify DNA
What are point mutations and frameshift mutations?
-change only one base pair
-Occurs via single base-pair substitution
-Phenotypic change depends on exact location
What are reversions and suppressors?
What is the ames test and its outcome?
The Ames test is a biological assay used to assess the mutagenic potential of chemical compounds.
How the Ames Test Works:
-Bacteria Strains: The test typically uses mutant strains of Salmonella typhimurium that cannot synthesize histidine (his⁻ mutants). Some versions also use Escherichia coli.
-Chemical Exposure: The bacteria are exposed to the test chemical, with and without metabolic activation (by adding liver enzymes from rats to simulate mammalian metabolism).
-Growth on Histidine-Free Medium: The bacteria are then placed on a medium that lacks histidine.
-Mutation Observation: If the chemical induces mutations, some bacteria may regain the ability to synthesize histidine (his⁺ revertants) and form visible colonies.
-Comparison with Control: The number of colonies in treated samples is compared to control plates to determine if the chemical significantly increases mutation rates.
Outcome of the Ames Test:
-Positive Result: A significantly higher number of colonies indicate that the test substance is a mutagen, meaning it causes genetic mutations.
-Negative Result: If no significant increase in colonies is observed, the substance is not mutagenic under the test conditions.
Dose-Response Relationship: A higher concentration of a mutagenic substance often leads to more mutations, strengthening the result.
What is chemical mutagenesis
Mutations can be corrected -DNA repair
1. Proofreading by DNA polymerase
2. Mismatch repair -errors introduced during replication are corrected
3. repair of thymidine dimers by
a) nucleotide excision repair (DNA Pol I and DNA ligase)
b) photoreactivation
What is physical mutagenesis
Mutations can be corrected -DNA repair
1. Proofreading by DNA polymerase
2. Mismatch repair -errors introduced during replication are corrected
3. repair of thymidine dimers by
a) nucleotide excision repair (DNA Pol I and DNA ligase)
b) photoreactivation
Describe microbial evolution in gene families
How does gene duplication and deletion drive microbial evolution?
Describe evolutionary selection and fitness
Explain genetic drift
What is gain of function?
Describe horizontal gene transfer
Homologous recombination:
-process that results in genetic exchange between homoloug DNA from two sources
Gene conversion: (homologous recombination results in replacement of recipient copy with donor copy). If no fitness benefit, deleted over time; if a fitness benefit, will persist
-Effective means for acquiring/evolving new functions/traits
Explain transformation
Explain conjugation
Conjugating (mating): horizontal gene transfer that requires cell-to-cell contact
-Plasma encoded
-Occurs between closely related or distantly related cells
-Donor cell contains conjugative plasmid
-Recipient cell does not contain plasmid
-Other genetic elements (e.g., other plasmids or host chromosomes) may be mobilized (transferred during conjugation)
What is transduction?
In transduction, DNA from the chromosome of one cell is transferred to another cell via a replicating virus (bacteriophage or phage)
Describe generalized transduction
Definition: Involves the random transfer of any part of the bacterial genome.
Mechanism:
A lytic bacteriophage infects a bacterial cell.
The phage replicates inside the bacterium and accidentally incorporates fragments of bacterial DNA into the new phage particles instead of viral DNA.
When these phages infect a new bacterial cell, they inject the bacterial DNA they are carrying.
This DNA may integrate into the recipient’s genome via homologous recombination, leading to genetic changes. It is otherwise lost
Describe specialized transduction
What are phyla and the 4 major categories
-Major lineages of bacteria
-80+ phyla can be distinguished based on 16S ribosomal RNA
-Proteobacteria
-Actinobacteria
-Firmicutes
-Bacteriodetes
How can you classify bacteria
Describe proteobacteria
What are alphaproteobacteria
Describe Rickettsiales
Alphaproteobacteria
