Bacterial Genetics Flashcards
define mutant
offspring of a normal member of a species
distinct from wild type
define mutation
any heritable change in DNA sequence
define allele
different forms of same gene
define isogenic strains
two lineages of same bacteria that have a single change
define selection
growth condition that allows for growth of only a specific kind of mutant
what are spontaneous base pair mutations
occuring by insertion of incorrect base during replication
what are induced base pair mutations
addition of external factors (mutagens) that alter chemical bonds in DNA and need repair
If the code is CCC (encodes proline) and it gets translated as CCA, CCG, or CCU (also encodes proline) - what type of mutation is this?
silent or synonymous mutations
change still results in same AA
If the code is CCC (encodes proline) and it gets translated to CGC (arginine) or GCC (alanine) - what type of mutation is this?
Missense or nonsynonymous mutation
If the code is CCC (encodes proline) and it gets translated to something with the loss of function - what type of mutation is this?
null mutation
In prokaryotes what two steps in DNA synthesis occur simultaneously?
transcription and translation
does a nonsynonymous mutation always lead to a change in phenotype?
no
Is a mutation always beneficial to the bacterium?
no
How is transcription terminated in bacteria?
factor dependent Rho
Rho binds rut sites not covered by ribosomes and progresses up mRNA until it hits RNA polymerase and dislodges it
what are nonsense mutation?
mutations that change from coding an AA to coding for a stop codon
what is a frameshift mutation?
base deletions or additions that alter reading frame of mRNA
changes function of protein
define vertical gene transfer
DNA replication provides daughter cell with copy of parental cell DNA
define horizontal gene transfer
evolutionary process that distributes genes between divergent prokaryotic lineages
How does DNA move between different bacterial species?
horizontal gene transfer
what is transformation in HGT?
uptake of naked DNA from environment and stable incorporation into the genome
what is transduction in HGT?
transfer of DNA by a virus or viral vector
what is transposition in HGT?
transposon genes are transferred from one organism to another through copying and insertion process
what is conjugation or mating in HGT?
transfer of genetic material between bacteria to direct cell to cell contact between two cells
what are bacterial species that are known for natural transformation/natural competence?
Streptococcus penumoniae
Neisseria gonorrhoeae
Haemophilus influenzae
what does it mean for a bacteria to be naturally competent?
can take up DNA from environment
How was natural competence discovered?
Griffith’s experiment
How does gram negative and gram positive preform transformation (HGT)?
translocation of ssDNA molecule into cell
How is competence regulated?
Quorum sensing - high bacterial species population > build up of CSP (competence stimulating peptide) > induction of competence
What is quorum sensing?
bacterial communication
relays number of cells in an environment based on a secreted protein or product
what is fratricide?
killing of neighboring non-competent cells as source of DNA
what is a bacterial species that is very good at transformation/competence?
Streptococcus
what is specialized transduction?
phage transfers small amount of bacterial DNA adjacent to phage DNA in chromosome
what is generalized transduction?
transducing phage - mutation leads to misreading at pac sites, carries bacterial DNA
what are the two types of transduction?
specialized and generalized
what is a bacteriophage?
bacterial virus
used in transduction
what is lytic grow?
phage replicates > lots of phages > lysis cell > virus in environment
what is lysogenic growth?
phage silently inserts into bacterial chromosome > no cell lysis
what is prophage or lysogen?
lytic genes repressed, viral DNA remains silent in host
what is conjugative transposons?
mechanisms of transposition
transposon excises from chromosome and circularizes then transfers (conjugation) to recipient and integrates into recipient DNA
what is conjugation?
transfer of DNA from donor to recipient cell
what is a F plasmid?
self-transmissible plasmid
has tra genes - encodes transfer apparatus
what are the two main functions of tra genes?
Dtr - DNA transfer and conjugal replication
Mpf - mating pair formation
what are the steps of conjugation?
- mating pair is established
- single strand of DNA is transfered
- DNA replication occurs in both donor and recipient cell
what are mobilizable plasmids?
dont encode own Tra apparatus
need Tra from self-transmissible plasmid or helper plasmid
what a hfr strain?
E. coli carrying F plasmid on chromosome
high frequency recombination
What does the mixing of Hfr and F- allow for?
conjugation
you can test for movement of genes with _____
selectable marker
The longer it takes for a gene to be transferred the __________ the road is is located in the chromosome
further down
What was the original map of E coli based on? Why?
based on minutes because of bacterial interrupted mating
what are pathogenicity islands?
Horizontally acquired sections of bacterial chromosome that encode genes primarily associated with virulence
How can you tell DNA is horizontally acquired?
look at close relatives
GC content
repeat sequences flanking genes
Salmonella pathogenicity islands
