Bacterial Genetics (8) Lecture

Question 1

Transformation

Answer 1

transforming a recipient cell into something else

two strains that can’t grow, put them together and if they transform maybe they will be able to grow

Question 2

Recombinants

Answer 2

result of transformation, have properties of original strains

Question 3

Griffiths Experiments

Answer 3

one strain killed mouse and the other did not
the lethal strain when heated did not kill mouse

dead lethal strain + non lethal strain = dead mouse

why? something was transforming and it was DNA

Question 4

Horizontal Gene Transfer

Answer 4

transfer of traits between cells

Question 5

What are the types of horizontal gene transfer?

Answer 5

1. Transduction (through phage)
2. Transformation (naked DNA)
3. Conjugation (fertility/mating of two cells)

Question 6

What must happen to the DNA once inside the cell?

Answer 6

the foreign DNA must integrate in to the hosts genome or be able to replicate independently which would mean it would have to be a replicon (has a origin of replication)

Question 7

What is the most common way of integration?

Answer 7

homologous recombination

gene on one strand has mutation and is switched out with non mutant gene - then the non mutant floats around and is degraded eventually

Question 8

What is the most common way for antibiotic resistance to happen?

Answer 8

horizontal gene transfer (transduction/transformation/ especially CONJUGATION)

Question 9

DNA mediated Transformation

Answer 9

uptake of naked DNA (takes up linear free floating DNA and incorporates into host chromosome)

Question 10

Competence

Answer 10

induction of gene to code products that lets bacterium take up DNA from outside and integrate it into the chromosome or “ability to take up DNA”

Question 11

Are all species competent

Answer 11

no, only certain species are naturally competent

Question 12

What is the result of DNA mediated Transformation?

Answer 12

replication will generate one wild type and then one recombinant

Question 13

DNase

Answer 13

enzyme that degrades DNA (so it would degrade naked DNA but not be able to get through cytoplasm)

Question 14

Which process of Horizontal Gene Transfer is sensitive to DNase?

Answer 14

Transformation - b/c takes up naked DNA

Question 15

Transduction

Answer 15

DNA is transferred via bacteriophage
- generally this is an error in phage replication cycle

two types: generalized and specialized

Question 16

generalized vs. specialized transduction

Answer 16

lytic or temperate phage = generalized (will produce transduction particles possibly aka phages that messed up and took host chromosome before being released)
temperate phages only = specialized (incorrect inexcision) - meaning that part of the phage DNA and part of the host DNA packaged making a defective phage

Question 17

Transducting particles

Answer 17

when original chromosomal DNA from the host is accidentally packaged into a phage making it a defective phage

• you could add a transducting particle to new cell to get a new trait

Question 18

Defective phage

Answer 18

lacks full phage chromosome can go into new cell and transduce new cell

Question 19

Conjugation

Answer 19

mating / probably responsible for most antibiotic resistance
requires cell to cell contact
involves a CONJUGATIVE PLASMID
- The F plasmid (fertility plasmid) serves as a model
- plasmid in-codes machinery for its own transfer
- F+ is the donor
- F- is the recipient
- F is the plasmid

Question 20

What are the two types of donors (in conjugation) we learned

Answer 20

F+ (transfers plasmid)

Hfr (transfers chromosomal DNA)

Question 21

What does F+ use to attach to F- ?

Answer 21

pilus

Question 22

What does F+ added to F- make?

Answer 22

two F+ cells

add one F+ to a bunch of F- and eventually all of them will be F+

both have copy of donor plasmid

Question 23

R-plasmids

Answer 23

resistance plasmids
encode resistance to antibodies/antibiotics
they are also conjugation
the plasmid has the origin of replication and the origin of transfer

Question 24

What is the significance of Hfr strains?

Answer 24

Hfr = high frequency recombination
used to map gene order for circular chromsomes
you can time the amount of conjugation then see what genes made it over in that time in order to map

Question 25

How is the Hfr strain formed?

Answer 25

F plasmid occasionally integrates into the chromosome creating one large chromosome then the F plasmid still preforms conjugation with the recipient but now drags some of the donors chromosome attached to the F plasmid over
cells inevitably separate before entire chromosome its transferred - you could separate them by shaking a tube