Chapter 17 - Microbial Genetics

Question 1

Horizontal Gene Transfer

Answer 1

process in which bacteria use to acquire new genes

Question 2

Conjugation

Answer 2

process by which donor bacteria transfers copy o a plasmid to a recipient bacterium through a pilus.

Question 3

conjugative plasmid

Answer 3

Located on donor cell, an extrachromosomal piece of dsRNA that codes for proteins necessary to make a threadlike filament known as a pilus

Question 4

pilus

Answer 4

Threadlike filament used to bind the recipient cell to the donor cell and brings them in close proximity.

Question 5

after pilus attachment?

Answer 5

Believed that a channel is then opened, allowing for a ssDNA copy of the plasmid to enter the recipient cell. Both cells make the complementary copy to the ssDNA, resulting in two new cells capable of conjugation.

Question 6

Transformation

Answer 6

Allows bacterial cell to acquire new genes, but it does not require cell-to-cell contact. Process in which genes acquired directly from environment.

Question 7

What is required for transformation?

Answer 7

A donor cell: lysed and released DNA into environment.

A recipient cell: takes up the DNA and incorporates into its own genome.

Question 8

When does transformation usually occur?

Answer 8

at the end of exponential phase of growth or beginning of the stationary phase, in the presence of high cell density and limited nutrients.

Question 9

What proteins are manufactured for transformation

Answer 9

DNA binding protein (DNA translocase), endonucleases, transmembrane channel proteins

Question 10

What do Gram Negative cells make for transformation?

Answer 10

Autolysin, to transport DNA across the outer membrane

Question 11

Translocase

Answer 11

Pull DNA binded to receptors on the outside of the cell into the cell, through the transmembrane channel

Question 12

transmembrane channel

Answer 12

a large structure often involving numerous different proteins

Question 13

endonuclease

Answer 13

used to degrade one strand of dsDNA when ssDNA can only pass, or cleave DNA fragments into smaller sizes.

Question 14

RecA

Answer 14

incorporates DNA into the bacterial chromosome so the genes can be expressed

Question 15

Transduction

Answer 15

Involves virus, a bacteriophage, to act as a conduit for shuttling bacteria genes from one cell to another. Negates cell-to-cell contact. 2 types of transduction (Generalized and Specialized)

Question 16

Generalized Transduction

Answer 16

Bacterial host infected w/ virulent or temperate bacteriophage engaging in lytic cycle.

Question 17

Generalized Transduction steps

Answer 17

1. Absorption 2. penetration 3. synthesis. When virus enters assembly stage, random pieces of bacterial DnA are mistakenly packaged into the phage head - results in transducing particle.

Question 18

What is the importance of a transducing particle?

Answer 18

Though not capable of infecting a cell conventionally, they can bind to a new bacterial host and inject their DNA inside. If this DNA is incorporated into recipients DNA, then the genes can be expressed.

Question 19

Specialized Transduction

Answer 19

Can only occur with temperate bacteriophage, involved lysogenic cycle of replication.

Question 20

Specialized Transduction steps

Answer 20

1. Bacteriophage attaches and injects viral DNA inside
2. DNA then integrates into chromosome of host cell (forms prophage)
3. Induction occurs, where prophage is excised from bacterial chromosome. Excision is incorrectly performed and portion of bacterial genes immediately adjacent to viral genes are excised too.
4. This means that all copies contain both viral and bacterial DNA.
5. Cell lyses and releases virions. Virions then inject into other bacteria.

Question 21

What’s unique about specialized transduction?

Answer 21

Since it contains both DNA from the virus and the bacteria, the second bacteria host that receives DNA from the virion has the ability to receive its own DNA, DNA from previous bacterial host and the viral DNA.

Question 22

What is homologous recombination

Answer 22

involves RecA protein. DNA from 2 sources are paired, based on similar nucleotide sequence in one area.

Question 23

Homologous Recombination - Strand Invasion

Answer 23

endonuclease nicks one strand, allowing RecA to pair up bases from different stands.

Question 24

Homologous Recombination - resolvase

Answer 24

cuts and rejoins DNA into two separate dsDNA molecules

Question 25

Site-specific recombination

Answer 25

process used by viruses to insert genome into chromosome of their host.

Question 26

Transposable elements - “jumping genes”

Answer 26

Responsible for the activation or inactivation of genes w/in an organism. Simple in structure, designed to move from one location to another w/in DNA (transposition)

Question 27

transposition

Answer 27

moving from one location to another w/in a DNA molecule

Question 28

transposase

Answer 28

enzyme responsible for allowing transposition to occur - all transposable elements code for this - short inverted repeats (IR’s) at each end

Question 29

Inverted repeat

Answer 29

Located at the ends of transposase

Question 30

insertion sequence

Answer 30

simplest transposable element - contains transposase and IR’s of varying lengths.

Question 31

transposon

Answer 31

contains additional genes, with the exact type varying widely from transposon to transposon - can be removed from 1 location and relocated to another

Question 32

cut-and-paste model (conservative transposition)

Answer 32

moving a transposon from 1 location and moving it to another location

Question 33

replicative transposition

Answer 33

a copy of a transposon that is inserted at a second site