Bacterial Genetics Flashcards
1
Q
bacterial genome
A
- no nucleus
- 4,000 genes
- haploid
- one chromosome
- extrachromosomal:circular plasmids/phages
2
Q
virulence factors
A
- enterotoxin (e coli, v cholerae)
- exfolioatin (s. aureus)
- erythrogenic toxin (S pyogenes)
- neurotoxin (C tetani)
3
Q
proportion of genome that encode protein/RNA
A
-humans have least, bacteria have the most, almost 80%
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
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
6
Q
regulation of gene expression
A
- nutritional status
- cell surface sensing
- quorum sensing
7
Q
operon
A
-cluster of genes whose expression is controlled by one promoter
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
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
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
11
Q
mutations in bacteria
A
- chemical modifying agents-base modifying, base analogs, intercalating
- physical agents-x rays, UV light
- also human carcinogens
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
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)
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
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
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
