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Microbiology/Immunology > Bacterial Genetics > Flashcards

Bacterial Genetics Flashcards

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Biology 101 flashcards
1
Q

bacterial genome

A
  • no nucleus
  • 4,000 genes
  • haploid
  • one chromosome
  • extrachromosomal:circular plasmids/phages
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2
Q

virulence factors

A
  • enterotoxin (e coli, v cholerae)
  • exfolioatin (s. aureus)
  • erythrogenic toxin (S pyogenes)
  • neurotoxin (C tetani)
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3
Q

proportion of genome that encode protein/RNA

A

-humans have least, bacteria have the most, almost 80%

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4
Q

expression of bacterial genes

A
  • promoter, RNA pol, reading frame, initiation, termination, makes mRNA
  • genes with related functions all share same regulatory elements and are an operon (eukaryotic each gene has it’s own)
  • regulated by metabolic processes or deficiencies rather than proteins interacting with the promoter
  • no enhancers, splicing, or post translational control
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5
Q

bacterial genotypes

A
  • minus sign means they cannot synthesize, digest, or resist things
  • no sign means it can
  • amp means the bacteria is ampicillan resistant
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6
Q

regulation of gene expression

A
  • nutritional status
  • cell surface sensing
  • quorum sensing
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7
Q

operon

A

-cluster of genes whose expression is controlled by one promoter

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8
Q

operator

A
  • promotor is separated from genes by operator (promoter-operator-lac genes that make operon)
  • regulates expression of operon
  • ex- Lac operon has an operator that a repressor fits into normally-if there is lactose around it binds to repressor and removes is from operator, turning the operon on
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9
Q

inducible expression

A
  • lac operon
  • has repressor in operator normally
  • lactose binds to repressor and removes it from operator
  • operon is on
  • whole thing induced by the lactose
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10
Q

repression

A
  • some genes are continually expressed because nothing is bound to operator
  • bacteria synthesize Trp using trp operon
  • if Trp is present, it binds to a trp repressor which binds to the operator and turns operon off
  • Trp represses the genes that would make more
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11
Q

mutations in bacteria

A
  • chemical modifying agents-base modifying, base analogs, intercalating
  • physical agents-x rays, UV light
  • also human carcinogens
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12
Q

Ames test

A
  • test used to determine if agent might be a carcinogen using bacteria-because they cause mutations in DNA
  • bacteria constructed to be his-
  • mutation will be reversed by mutagen to his+
  • put mutated bacteria on plate with disc containing chemical
  • if it is a mutagenic agent, the bacteria will revert (mutate) and make histidine again- positive result
  • if not mutagenic, bacteria will remain his-

-cigarette smoke, aflatoxin, charred hamburger, 2-aminofluorene

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13
Q

gene exchange in bacterial experiment

A
  • one bacteria without capsule and after prolonged cultivation in vitro is harmless (live)
  • other bacteria with capsule is lethal unless killed
  • combined live harmless and dead lethal (now harmless) and the combination is lethal
  • the virulence factors from the dead genome jumped into live virus and made it lethal (transformation)
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14
Q

transformation

A
  • DNA released from dead bacteria may be taken up non-specifically by live bacteria
  • if it is not digested by restriction enzymes, it may be incorporated into the recipient genome by homologous recombination
  • allowed s pneumonii to be transferred
  • DNA might be chromosomal or plasmid
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15
Q

gene exchange in bacteria

A
  • transformation
  • transduction
  • conjugation
  • relatively rare due to restriction enzyme activity
  • bacteria recognize self by methylation patterns
  • usually prevents recombination
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16
Q

conjugation

A
  • F plasmid- large F=fertility
  • F is male, F- is female
  • plasmid integrates into bacterial chromosome
  • can separate from chromosome with incorporated host genes
  • F plasmid encodes ability to transfer itself to a bacterium that lacks it
  • F bacterium forms a sex pilus and transfers the DNA from the integration site and the plasmid to the new bacterium
17
Q

types of bacteria (F)

A
  • F- female
  • F+ male without integration
  • Hfr- male with integrated plasmid
18
Q

generalized transduction

A

-bacteriophage (lytic phage) can infect bacteria and cause lysis- releases DNA that can be taken up by the phage and carried into another bacterium

19
Q

specialized transduction

A
  • lysogenic phage can insert itself into the bacterial chromosome (lysogeny, producing a prophage in the chromosome) and later excise themselves with some adjacent bacterial DNA which can be carried to another bacterium
  • transfer of toxins of diptheria, botulism, cholera, scarlet fever
20
Q

R factors

A

-segments of non-chromosomal DNA that carry genes for antibiotic resistance

21
Q

transposons

A
  • some genes that can move around the genome
  • encode transposase enzyme gene, a repressor that stops the expression of the transposase, and typically a drug resistance gene
  • relocation of the transposon might bring it into a site where the F plasmid or where the bacteriophage might integrate, thus allowing the transposon to be moved into another bacterium
  • can contain several virulence genes:pathogenicity island
22
Q

pathogenicity islands

A
  • several adjacent genes that contribute to pathogenesis of a disease
  • gram neg rods
  • some e coli are toxic and some are not
  • transferred by other means-dont have an intrinsic relocation mechanism
  • superantigens
  • toxin delivery systems
  • different than bacteriophage and plasmid that usually encode only one gene
23
Q

S. aureus virulence

A
  • gained penicillin, aminoglycosides, trimethoprim from F plasmid
  • gained vancomycin A and B from F plasmid from E. fecalis
  • mutation lost methicillin receptor- made it resistant
24
Q

summary

A
  • gene expression depends on operon, operators, repressors
  • exchange DNA by transformation, transduction, conjugation
  • exchange of DNA changes bacterial virulence and resistance to antibiotics

Microbiology/Immunology (18 decks)

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