Bacterial Genetics Flashcards
plasmids
double-stranded, often circular DNA sequences that are capable of autonomously replicating in a host cell
*NOT part of the core chromosome
genomic thrift
majority of bacterial genome is coding for something (selects for rapid growth, ditching genes that slow them down/are not super important)
unique functions that a plasmid may provide a host bacteria
-antibiotic resistance
-toxin production
-novel biochemical functions or surface molecules
copy and paste (retro) transposons in bacteria
replicative
cut and paste transposons in bacteria
conservative (no additional copies)
operons
*bacterial genes organized in clusters of related genes
*genes in an operon turn on or off TOGETHER
*a single promoter regulates all of the genes in an operon
*allow efficient use of resources and genomic space (only express the genes when needed)
operon for vancomycin resistance
when vancomycin is sensed, the cell switches to making an alternative cross-linker to function in presence of antibiotic
*switches back to off when no vancomycin present
how do bacteria divide / replicate
binary fission
wild-type bacteria
description of a bacterium that is found MOST ABUNDANTLY in nature
mutant bacteria
bacterium that differs genetically from the wild-type; the mutant has a genotype different from the wild-type strain, which may or may not result in a readily observable trait
2 primary mechanisms for generating genetic diversity in bactera
- vertical transmission - spontaneous and random mutations and selection for bacteria with enhanced properties (slow)
- horizontal transmission - gene transfer from other microorganisms (rapid)
4 mechanisms of horizontal gene transfer
- transformation
- transduction
- conjugation
- transposition
horizontal gene transfer: transformation
*uptake by a bacteria of naked DNA
*find DNA in the environment and put it into its own chromosome
*can occur between unrelated bacteria and between domains
examples of transformation in real life
*strep. pneumoniae
*haemophilus influenza
*can acquire capsule protein (virulence factor)
horizontal gene transfer: transduction
*infection of non-lethal virus carrying bacterial genes
*acquisition of genes from a BACTERIOPHAGE (injection of DNA)
lytic phages
phages that cause KILLING of host bacterium
lysogenic phage
phage that can survive in the bacterium without killing; usually integrated into the bacterial chromosome
temperate phage
phage capable of undergoing BOTH lytic or lysogenic development
virulent phage
phage capable of undergoing ONLY lytic development
lysogen
bacterium harboring a lysogenic phage
examples of transduction
*many bacterial exotoxins coded for by phages
1. group A strep
2. clostridium Botulinum
3. vibrio Cholerae
4. Corynebacterium diphtheriae
5. Staph aureus
6. E. coli (shiga toxin)
ABCDs for 5 bacterial toxins that are encoded in a lysogenic phage
restriction systems that limit transduction
- methylating enzyme protects DNA
- endonuclease cuts unmethylated DNA
horizontal gene transfer: conjugation
*plasmid-mediated exchange of information between bacteria in contact
*can NOT go between gram + and gram -
*not all plasmids are conjugative
horizontal gene transfer: transposition
*exchange of genetic information via mobile genetic elements (transposons)
*can be cut and paste or copy and paste
*inverted repeats at either end of the transposons
mecA and MRSA
*mecA is carried on a mobile genomic element (transposon)
*encodes an ALTERED PENICILLIN BINDING PROTEIN
*causes resistance to beta-lactam antibiotics
drug-resistance of Neisseria gonnorhea
swaps out the pilin genes to hide from our immune system
