lecture 4 - genetics: microbes and humans

Question 1

genome

Answer 1

all genes in an organism

Question 2

chromosome

Answer 2

DNA molecule that contains genes

-plasmids also carry genes in bacteria

Question 3

gene

Answer 3

segment of DNA that codes for protein or RNA

Question 4

what are plasmids

Answer 4

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”

Question 5

sexual reproduction

Answer 5

• in sexual organisms like humans
• need 2 parents to have sex
• sex generates new combination of genes

Question 6

what are offspring of sexual reproduction?

Answer 6

subsets of parent genes (not “mix” because then all siblings would be the same)

Question 7

asexual reproduction

Answer 7

• Bacteria reproduce asexually
• One cell divides into two identical daughter cells
• Each daughter gets full copy of parent’s genes
• No gene mixing

Question 8

how do organisms evolve with asexual reproduction

Answer 8

• heritable variation in genes
  1. horizontal gene transfer
  2. random mutatons

Question 9

Horizontal Gene Transfer (HGT)

Answer 9

• 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

Question 10

how does HGT affect evolution?

Answer 10

• 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

Question 11

what are the three mechanisms of HGT

Answer 11

Conjugation
Transformation
Transduction

Question 12

explain conjugation of HGT

Answer 12

• *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

Question 13

how do plasmids and HGT contribute to antibiotic resistance?

Answer 13

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

Question 14

explain transformation of HGT

Answer 14

• 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

Question 15

explain Fred Grifts expieriemet involving HGT 1928

Answer 15

• 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)

Question 16

explain transduction HGT

Answer 16

• 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

Question 17

in terms of plasmids what does incompatibility mean?

Answer 17

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)

Question 18

plasmid copy number

Answer 18

number of copies in a cell

-can be from 1 to 1000s

Question 19

what are the three forms of plasmid mobility?

Answer 19

• 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

Question 20

what are the three ways that plasmids facilitate resistance?

Answer 20

*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

Question 21

what is a point mutation? what is the effect?

Answer 21

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

Question 22

how common are point mutations

Answer 22

• 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