Bacterial Genetics Flashcards
T/F Bacteria are adaptable.
True
What does the bacterial genome consist of?
An organisms complete set of DNA:
- chromosome- essential and nonessential proteins
- plasmids
- bacteriophage- prophage
- IS elements, transposons, PAI’s (GEI’s)
- integrons
Bacterial chromosome? shape?
- one, circular, dsDNA (majority), some have more than one, some are linear
- no histones or introns
- encodes for essential and non essential genes, better fit to survive in environment
- not housed in a membrane bound nucleus, but nucleiod, a region of the cell where the chromosome resides
Are bacteria haploid or diploid?
haploid -one copy of each gene, mutations are expressed from mother to daughter
Bacterial gene expression? essential vs nonessential?
- genes required for basic survival are constitutively expressed (DNA, cell wall, RNA, translation)
- expression of non essential genes can be positively (inducers) and negatively (repressors) regulated, usually at the level of transcription, some genes are present on DNA as operons
- operons
- polycistronic mRNA
What are operons?
sequence of DNA that contains multiple genes to produce multiple proteins for a single purpose (not in eukaryotic cells), multiple genes coordinately expressed
-multiple genes with single promoter
Polycistronic mRNA?
mRNA that has information for more than one gene or protein product
-there are sites where ribosome can bind to get independent proteins
What do bacteria adapt to?
they quickly adapt to environmental changes for survival by modulating gene expression
- availability of sugars
- iron concentration
- presence of an antibiotic
what is an example of regulation for survival in bacteria?
the Lac operon
- when glucose is available the lac operon encodes genes that allows for metabolism of lactose
- using regulators and repressors, allosteric changes
- positive and negative regulation
- adapts to environmental changes to survive
What is gene regulation by quorum sensing? low vs high density
- organism can change its phenotype based on density of bacteria
- low density- signal molecules for harmless type
- high density- signals bind receptors that bind upstream of genes to make organism more pathogenic by making biofilm of special toxins
The expression of many virulence genes are under regulation at the level of ______.
transcription
What are the mechanisms of mutations in bacteria?
- base substitution or point mutation (transition or transversion), G->A, G->C
- deletion or addition of nucleotides
- insertional mutation- disruption of a gene by a transposon (jumping gene)- makes organism more pathogenic
- recombination
Results of mutations?
- missense mutation- changes in amino acids sequence of protein product
- frameshift mutation- shift in reading frame of gene
- inversion mutation- segment of DNA is removed and reinserted in reverse direction
- inactivation of gene
Clinical significance of mutations?
- changes in amino acids of bacterial structures can result in resistance to antibiotics
- non resistant bacteria multiply, some develop mutation, non resistant bacteria die from antibiotic, drug resistant mutations thrive
- base mutations, frameshift and gene arrangements can cause antigenic and phase variation of major surface components
- antigenic variation
- phase variation
antigenic variation?
- changes in composition or structure of a molecule
- pilli on organism is changed because amino acids look different, antibodies used need to be different
- population- shift back and forth
Bacteriophage? structure? genome?
viruses that infect bacteria:
-specific, used to subtype bacteria (phage typing)
structure:
- protein capsid that houses genome
- may have base and tail
- no membrane envelope
Genome:
- DNA or RNA
- single or double strand
- linear or circular
What is horizontal gene transfer?
- lateral gene transfer (LGT)
- tranformation
- conjugation
- transduction
Transformation?
donor -> cell lysis: release DNA fragments -> DNA enters recipient cell and integrates into DNA
- uptake of naked DNA by bacteria in state of competency
- under right conditions, the DNA can be incorporated into genome of recipient and result in change in phenotype
- naturally competent DNA have the ability to take up exogenous DNA across membrane without manipulation (strep, neisseria, gonorrhoeae)
Conjugation?
- intimate association with two individuals, cell contact
- male (F+) and female (F-) cells come together
- conjugative plasmid makes copy of itself and shares it with F-
- after reaction, there are two F+ cells
- conjugative transfer of plasmids with resistance genes is an important cause of spread of antibiotic resistance
- Gram - use pili and Gram + use other systems
- some transposons are conjugative
Transduction?
- transfer of genetic info from one bacteria to another by bacteriophage
- prophage- DNA incorporated into chromosome
- lysogenic conversion
- donor organism goes through lytic phase with temperate phage
- takes up DNA from donor and its own DNA to make progeny
- infects another organism, DNA from donor will recombine with genome of recipient
- transduction and conjugative play important role in antibiotic resistance
Vancomycin method of action? bacteria method of resistance to it?
MOA:
-interacts with D-alanine, D-alanine termini, prevents cross linkage of peptidoglycan layers
MOR:
- change of binding site to D-alanine, D-lac
- thickening of cell wall that traps vancomycin
