lecture 4 - genetics: microbes and humans Flashcards
genome
all genes in an organism
chromosome
DNA molecule that contains genes
-plasmids also carry genes in bacteria
gene
segment of DNA that codes for protein or RNA
what are plasmids
loops of DNA separate from the host chromosome
- prokaryotes like bacteria.
- either in DNA or RNA form never both
- -replicate using host machines
- non-essential but carry genes that act as “cheat codes for survival”
sexual reproduction
- in sexual organisms like humans
- need 2 parents to have sex
- sex generates new combination of genes
what are offspring of sexual reproduction?
subsets of parent genes (not “mix” because then all siblings would be the same)
asexual reproduction
- Bacteria reproduce asexually
- One cell divides into two identical daughter cells
- Each daughter gets full copy of parent’s genes
- No gene mixing
how do organisms evolve with asexual reproduction
- heritable variation in genes
1. horizontal gene transfer
2. random mutatons
Horizontal Gene Transfer (HGT)
- A few genes are transferred from donor cell to recipient cell
- new cells can be passed to daughter cells
- -not sex
- between chromosomes is rare
- by plasmids is more often
how does HGT affect evolution?
- acquisition of beneficial genes
- potential to invade new niche and speciate
-ex) e.coli requires genes for attachment (genes to make pili) .now e.coli has ability to stick to urethra and cause UTI
Ex) changes in metabolism - e.coli can eat lactose where salmonella can not (ecoli survive in infant gi track
what are the three mechanisms of HGT
Conjugation
Transformation
Transduction
explain conjugation of HGT
- *what a plasmid does; active.
- plasmid wants to replicate therefore makes bacteria host give another copy to another host – like a genetic infection in bacteria
- pillis bridge forms between donor and recipient cells
- F factor (plasmid) is copied from donor into recipient cell
how do plasmids and HGT contribute to antibiotic resistance?
Plasmids can carry antibiotic resistance genes, especially in clinical setting
- Antibiotic resistance ensures that the plasmid is essential to the cell, so is maintained
- plasmid genes can move between species - can spread a. resistance to different pathogens
explain transformation of HGT
- free donor DNA fragment is transferred into live recipient cell
1. natural - bacteria eat DNA (binds and is ingested into cell to be degraded) sometimes acquires portions of these genes.
-if eat antibiotic resistant gene they can acquire this
explain Fred Grifts expieriemet involving HGT 1928
- has staphococcus pneumoniae (pathogen) deadly to mouse
- produces capsule that forms slimy environment
b) single mutation to delete capsule and then get “rough cells” become non-pathogenic - number c he gave mouse heat killed capsuled form to mouse and mouse good
d) Game mouse dead capsid and live Rough cells mouse dies - dna passed from dead cells to live cells and was able to infect host (kill mouse)
explain transduction HGT
- passive process mediated by virus (phage) infecting bacteria
- accidental
- virus infects bacteria cell and replicates its DNA accidentally packaging some bacterial DNA as well- gives that dana to other bacteria when transmission occurs
in terms of plasmids what does incompatibility mean?
you can have all kinds of different plasmids in a cell but not two of the same because they need to use the same copy machines at the same time (competition)
plasmid copy number
number of copies in a cell
-can be from 1 to 1000s
what are the three forms of plasmid mobility?
- how they enter and exit cells (if they aren’t beneficial cell usually drops them through cell division - only ones that don’t have resources to replicate (low copy number))
- Conjugative: Contain all genes to facilitate their own transfer to other cells
- Mobilizable: Contain some transfer genes, and cannot be transferred in the absence of a conjugative plasmid
- piggy back with another C.P.
-Non-mobile: only replicate through vertical gene transfer
(cant move from cell to cell with
what are the three ways that plasmids facilitate resistance?
*carry genes that encode for …..
1. Efflux pump (allows cell to take antibiotics, but this will pump everything out and thus kill a cell)
2, Antibiotic degrading enzyme
3. Antibiotic altering enzyme
what is a point mutation? what is the effect?
change in one base pair of a genome.
-changes what amino acid or protein that genome codes for
“single nucleotide polymorphism (SNP)”
-most are harmless
-example:
Wild-type: healthy gene for hemoglobin (CTT codon for dana)
-mutation of one base codon from T to A
-rather than coding for healthy hemoglobin, now you have sickle cell hemoglobin
-usually not advantageous unless in malaria stricken environment
how common are point mutations
- 1 SNP every 300 base pair (bp) human (3000000000 bp)
- For every 10000000 possible snp
- Parent offspring 50 more snp that parent didn’t have
- How evolution occurs
