Test 3-3

Question 1

episome

Answer 1

when a plasmid integrates itslef into the bacterial chromosome

Question 2

temperate phage

Answer 2

bacteriophage that stabily integrate their DNA into host cell DNA

Question 3

lytic phage

Answer 3

bacteriophage that replicates inside and lyses the bacterium

-immediately goes into viral mode

Question 4

three forms of DNA transfer in bacteria

Answer 4

tnsformation - direct uptake of DNA material from environment
conjugation - sex pili
transduction - with viruses

Question 5

Homologous recombination (HR) definition

Answer 5

An exchange of genes between different pieces of DNA.
-need to stabilize linear pieces of DNA that the bacteria wants to take up and use
-must be some similarity between the genes (like similar alleles)
-

Question 6

Homologous recombination (HR) purpose

Answer 6

Stabilizes genes from DNA the bacterium has acquired by transformation, conjugation or transduction.

Question 7

Homologous recombination (HR) process

Answer 7

1) Short, linear pieces of DNA exchange genes with a homologous region of genes (i.e. alleles) on the bacterial chromosome.
2) A recombination protein is required for HR to occur. The most common is recombination protein A, or recA (SWAPS THE GENES)
3) Linear DNA (the OLD genes that the bacteria used to have) is broken down by cellular exonucleases, therefore it is not stable in the bacterium.
4) Genes that are incorporated into the bacterial chromosome become a permanent part of the cell’s genome.

Question 8

transformation definition

Answer 8

Uptake of free DNA from the environment.

Question 9

transformation purpose

Answer 9

Acquire new traits by utilizing the DNA from a dead bacterium.

Question 10

transformation process

Answer 10

1) A dead bacterium releases its DNA into the environment.
2) Segments of the free DNA are taken up by a viable bacterium.
3) If the DNA segments share homology with the bacterial chromosome, some genes can be stabilized by HR.

Question 11

conjugation definition

Answer 11

Genes are transferred from one bacterial cell to another through cell-to-cell contact.

Question 12

conjugation purpose

Answer 12

Acquire new DNA from another viable bacterium.

Question 13

conjugation process

Answer 13

1) “Fertility factors” supply all needed components, e.g. the sex pili which establishes a bridge between two bacterium.
2) Single-stranded DNA is transferred from a “donor” cell (which has the fertility factor) to a “recipient” cell.
3) Chromosomal DNA transfer: Genes have to be stabilized by HR, since the linear DNA would be degraded.
4) Plasmid DNA transfer: DNA circularizes and becomes stable without HR.

Question 14

fertility factor

Answer 14

1) tra operon = encodes sex pili and other proteins needed for conjugation
2) oriT = a.k.a. “origin of transfer”; a single-strand break occurs here to initiate the transfer of DNA to another bacterium

Question 15

F neg cells

Answer 15

Recipient cells only - cannot initiate conjugation bc no F-factor

Question 16

in every cross there must be one ____ cell

Answer 16

F neg

Question 17

F+ cells

Answer 17

have fertility factor as a plasmid

Question 18

Hfr cells

Answer 18

have fertility factor integrated into bacterial chromosome – episome (high frequency)

Question 19

F+ X F- conjugal cross

Answer 19

1) sex pilus first formed - bridge forms
2) (unwinding at oriT) oriT transfered (as single strand) first following the rest of the plasmid
3) last gene transfered is the tra operon
4) F-cell becomes F+ cells (sex change)

Question 20

Hfr X F- conjugal cross

Answer 20

1) sex pilus fromed and bridge formed
2) (unwinding at oriT) oriT transfered (as single strand) first following the rest of the Hfr DNA
3) Hfr bridge is usually broken off before complete transfer is done so most likely only a partial transfer
4) F- cells needs to do HR to stabilize single strand now - F-factor does NOT COMPLETELY TRANSFER –> new DNA is incorporated
5) F- cell DOES NOT go through sex change

Question 21

transduction definition

Answer 21

Transfer of bacterial DNA to another bacterium using a phage vector

Question 22

phage types

Answer 22

1) Virulent phage – Undergoes lytic replication
2) Temperate phage – Can undergo lytic replication or lysogeny (integration of phage DNA into a specific site on the bacterial chromosome)

Question 23

transduction process

Answer 23

1) A lytic phage mistakenly incorporates bacterial chromosomal DNA into its phage head.
2) When that phage infects another bacterium, that bacterial DNA can be utilized by the other bacterium if it is stabilized by HR.

Question 24

Specialized transduction:

Answer 24

• NEEDS Temperate phages, i.e. phages that incorporate their DNA into their bacterial host DNA (a.k.a. “lysogeny”), can remove bacterial genes when the phage excises its DNA to undergo viral replication.
• Excised bacterial DNA can be transferred to a new bacterial host.
• Only bacteria genes that are close to the phage insertion site can be excised.
• Transferred bacterial genes must be stabilized by HR.
• limited to genes near the incorporated phage DNA

Question 25

3 types of antibiotic resistance

Answer 25

intrinsic
chromosome mediated
plasmid mediated

Question 26

intrinsic resistance

Answer 26

• This form of drug resistance can’t be transferred between bacteria, therefore intrinsic resistance is not increasing among bacterial populations.
• Lacking a target molecule for a specific drug or having structural or physiological barriers renders the bacteria intrinsically resistant to a drug.

Question 27

chromosome mediated resistance

Answer 27

• Bacterial chromosomal genes encode this form of resistance.
• Generally, the gene products modify the antibiotic binding targets so that drug binding cannot occur.

Question 28

plasmid mediated resistance

Answer 28

• Resistance genes are located on plasmids.
• Commonly, plasmids encode proteins that degrade (e.g. β-lactamase) or modify (e.g. acetyltransferase) a drug or act as an efflux pump to remove the drug from the cell.
• Transfer of plasmids between bacteria species is responsible for the rise of multiple drug resistant bacteria.

Question 29

resistance factor (R-factor) components

Answer 29

• plasmid that has antibiotic resistance has this factor
• Resistance transfer factor – equivalent to an F-factor because it encodes all of the constituents needed for conjugation.
• Resistance determinant (a.k.a. R-determinant)- the gene(s) for drug resistance. This part of the plasmid has “hot spots” (insertional sequences) for transposons to help create multi-drug resistance plasmids.

Question 30

How are multiple drug resistance plasmids assembled?

Answer 30

• –>Resistance gene cassettes - Bacterial DNA typically carrying a single gene that encodes antibiotic resistance, but without a promoter.
• –>Integrons - Genetic elements in bacteria which express and is capable of acquiring and exchanging ‘resistance gene cassettes’.
• -An integron is a three component gene capture and dissemination system which is found in plasmids, chromosomes and transposons.
• A gene encoding a site-specific recombinase (“integrase”) along with a specific site for recombination
• Segments of DNA called gene cassettes
• A promoter to drive gene expression
• –>Transposons – a.k.a. transposable elements or “jumping genes” that may contain an integron containing one or more drug resistance genes.

Question 31

transposons

Answer 31

• Mobile DNA elements that can transfer themselves (or a copy) from one molecule of DNA to another
• Present in both eukaryotic and bacterial cells, as well as viruses
• Transposons can jump between two chromosomes, two plasmids or between one of each=As a result, multi-drug resistance plasmids can be constructed and passed between bacterial species.

Question 32

simplest transposon contains

Answer 32

• Indirect repeat sequences on each end, which are opposite strands of double stranded DNA read identically from opposite ends. Needed for recognition by the transposase.
• A single gene for transposase, an enzyme required for transposon movement (“jumping”)

Question 33

indirect repeats are (transposons)

Answer 33

the sequence of DNA that tells the transposase where to chop out DNA to jump it