Microbio Wk 7

What is a genotype?

genetic makeup of an organism

What is a phenotype?

characteristics that are expressed - manifestation of genetype

What are genomes?

total genetic information in the cell

What is a core genome?

pools of genes shared by all members of a bacterial species

What is an accessory genome?

pools of genes present in some but not all genomes within the same bacterial species

What are pangenomes?

global genome repertoire of a bacterial species (core genome + accessory genome)

What are metagenomes?

global gene repertoire of a mixed microbial population

What is the bacterial chromosomal structure?

generally have one circular chromosome, although very rarely a species might have two or three

What is chromosomal replication?

-DNA needs to be unwound for replication (DNA gyrase: target for antibiotics) -leading strand and a lagging strand -complementary bases -semiconserved replication -replication begins at a specific site (origin of replication)

What is bidirectional replication?

-DNA is synthesised in both directions creating a replication bubble between both replication forks -replication terminates when the replication forks meet

What is involved in plasmid replication?

-replication -multimer resolution -partition -post segregational killing

What is replication in plasmid replication?

plasmids must replicate to ensure sufficient copies exist in each daughter cell

What is multimer resolution in plasmid replication?

after replication plasmids must separate

What is partition in plasmid replication?

low copy number plasmids need to physically redistribution to both daughter cells

What is post segregational killing?

plasmid free daughter cells lose viability

What are genome dynamics?

bacterial genomes are dynamic and changes to the content or organisation occurs over time

What are genetic mutations?

-results in a change to the composition of the DNA and can arise in one of two ways: induced, spontaneous

What is induced (genetic mutations)?

-exposure to environmental mutagen (e.g. UV radiations) -deliberate

What is spontaneous (genetic mutation)?

-without external intervention -errors in DNA replication

What are types of mutations?

-point mutations -reversion -frameshift mutation

What is point mutations?

-substitutions that only change one base pair -missense -nonsense -silent -genetic codon tables have redundancy

What is reversion?

point mutation that is restored to the original sequence

What is frameshift mutation?

change the reading frame

How does bacteria repair DNA?

-if DNA damage is repaired before a cell divides, then no mutation has occurred (heritage) -DNA damage induces the SOS repair system -some repair is error free; other types leave mutations that are less damaging than the original change

What is frequency of mutation?

mutation rate = probability that a gene will mutate when the cell divides

What does the mutation rate depend on?

the frequency of mutation and efficiency of DNA repair

What do mutagens do?

increase the rate of spontaneous mutation

What is homologous recombination?

-exchange of DNA between two molecules -crossing over -DNA repair or horizontal gene transfer

What is vertical gene transfer?

-through bacterial division from original cell to daughter cells -DNA/chromosome replication

What is horizontal gene transfer?

transfer of genes from one bacteria to another of the same generation

What is transformation horizontal gene transfer?

-'naked' DNA is transferred to recipient cell -discovered in 1928 in strep. pneumoniae -requires recA for recombination -recipient cell needs to be competent (which means it must be in a physiological state to take up the DNA) -recombinant cell

What is transduction horizontal gene transfer?

-DNA is transferred from the donor to the recipient cell via a bacteriophage generalised or specialised -transductant

What is Conjugation (horizontal gene transfer)?

mediated by a special type of plasmid and requires cell-cell contact via the sex pilus -donor cell must contain the plasmid and the recipient cell does not -F factors = fertility factor plasmid

What are plasmids in mobile genetic elements?

-extrachromosomal DNA -most do not contain essential genes instead carry virulence and antimicrobial resistance genes or genes for specialised metabolism -plasmids are usually smaller and can be circular or linear

What are different types of mobile genetic elements?

-pathogenicity islands -transposons -integrons -bacteriophage

What are pathogenicity islands (mobile genetic elements)?

regions of bacterial chromosome acquired through horizontal gene transfer

What are transposons (mobile genetic elements)?

pieces of DNA that change location in the genome

What are integrons (mobile genetic elements)?

gene cassettes that carry virulence or antimicrobial resistance genes

What are bacteriophage (mobile genetic elements)?

carry virulence genes