3-2: Prokaryotic Genetics Flashcards
How are genes named
First three letters describe function, fourth designated specific gene
Italicized, last letter capitalized
Example of gene name
btuC (Vitamin B12 Uptake, gene C)
How are proteins named
Same, but not italicized and first letter also capitalized (e.g. BtuC)
What is a mutation
Heritable change in the DNA sequence of a genome (substitution, insertions, deletions)
What is the wild-type strain
Strain isolated from nature or parent strain
What is the phenotype. Eg.
Observable characteristics of an organism
E.g. metabolic, virulence, morphology
What is a genomic locus
a specific position on a gene
How are mutations named
Add number to gene name
e.g. hisC1
How is a deletion mutation shown
Delta symbol
How are phenotypes named
Three letters with (+) or (-) symbol
His+ can make histidine
How do we isolate mutagens
Can induce mutations
Can isolate mutants by selection (parent does not grow)
Example of something you can select for to isolate mutant
Antibiotic resistance
How do you use indicator plates for screening
Phenotype linked to colony appearance (colour, fluorescence)
How do you use indicator plates for screening
Phenotype linked to colony appearance (colour, fluorescence)
What is a point mutation
Mutation to a single base pair within a protein-coding sequence
What are the three kinds of point mutations
Silent (different codon, same aa)
Missense (one aa to a different aa)
Nonsense (change in aa to stop codon; premature end to protein)
What is truncation
The premature end to a protein sequence due to a nonsense mutation
What is a deletion vs insertion mutation
Deletion: DNA lost
Insertion: DNA added
What can deletion or insertion mutations lead to
Frameshift mutation (shifts all downstream codons, scrambles sequence) = disruptive
What is a reversion
Mutant that acquires another mutation and reverts back to wild-type
What is a suppressor mutation
Mutation that compensates for the effects of a prior mutation
What is the natural mutation rate of prokaryotes
10^6 to 10^7 per 1000 base pairs per round of replication
What is horizontal gene transfer
Acquiring new genetic material (foreign DNA) from the environment
Three ways foreign DNA can enter prokaryotic cells
Transformation
Transduction
Conjugation
What can happen to the DNA once it is inside the cell (horizontal gene transfer)
Be degraded
Replicate as separate entity (phage)
Be integrated into chromosome (recombination, transposition)
What can happen to the DNA once it is inside the cell (horizontal gene transfer)
Be degraded
Replicate as separate entity (phage)
Be integrated into chromosome (recombination, transposition)
Physical exchange of DNA between genetic elements of the same cell
Genetic recombination
Important type of genetic recombination
Homologous recombination
What does homologous recombination do
DNA repair mechanism (double strand breaks), horizontal gene transfer, genome rearrangements (deletions, insertions)
What is the main protein in homologous recombination, what does it do
RecA, binds ssDNA, searches for homologous dsDNA, mediates strand invasion
What happens during homologous recombination
DNA strand from one source (chromosome) fused to DNA strand from another (foreign DNA)
What is a transposable element
Mobile genetic element, can be inserted into another DNA source
What enzyme is involved in transposition. What does it do
Transposase enzyme
Recognize inverted repeats, cleaves transposable element of DNA, cleaves another DNA and inserts transposable element into it
What are the two kinds of transposable elements
Conservative (cut and paste)
Replicative (copy and paste)
What are transposons used for in lab
Generate mutant strains
Process by which free DNA is incorporated into a recipient cell bringing about genetic change
Transformation
Where does the DNA for transformation come from
Lysed cells within their environment
How does DNA cross the cell membrane
Cell needs to actively take it up (regulated process)
What is it called when cells can take up free DNA
The cell is competent
How is DNA captured in competent cells
Pili captures it, retracts, one stand of DNA degraded and other passed through cm
What is a bacteriophage
Virus that infects bacteria
What is a viruses DNA packaged into
Virions
What are the two bacteriophage pathways
Lytic pathway: DNA replicated into new particles using host resources, lyse cell and release to infect new
Lysogenic pathway: viral DNA integrated into host DNA (prophage)
What is a temperate phage
One that can operate via lytic or lysogenic pathway
What is transduction
Virus transfers bacterial DNA from one cell to another
What are the two kinds of transduction
Generalized transduction: during lytic cycle, host cell DNA accidentally packaged into viral particle, injected into new cell
Specialized transduction: after prophage forms, its DNA is excised from genome but some neighboring host DNA is also packaged then injected into new cell
What is conjugation
Horizontal gene transfer requiring cell-cell contact
“mating”
What mediates conjugation
Conjugative plasmids
What is the F plasmid
Fertility plasmid
Strains with F plasmid = F+ = donor cell
What kinds of cells can mate
F+ (donor) and F- (recipient) only
What kind of pilus do F+ cells encode
Conjugative pilus
What does the conjugative pilus do
Attaches to other cell, brings them together, forms conjugative bridge
What secretion system is used in conjugation
Type four
Transfers F plasmid DNA from F+ cell to F- cell
What is an Hfr cell
Insertion sequence of F plasmid integrates into chromosome of recipient
Part of donors chromosomal DNA transferred
Donor DNA incorporated into recipient genome
Full F plasmid not transferred, recipient is still F-
What acquired genes will be maintained
Those that provide a selective advantage
What happens to most acquired DNA
Lost
