Chapter 7: Genetic Transfer and Mapping in Bacteria and Bacteriophages

Question 1

minimal medium

Answer 1

a growth medium that contains the essential nutrients for a wild-type (nonmutant) bacterial species to grow. Researchers often study bacterial strains that harbor mutations and cannot grow on minimal media. A strain that cannot synthesize a particular nutrient and needs that nutrient to be supplemented in its growth medium is called an auxotroph. A prototroph does not need this nutrient in its growth medium.

Question 2

auxotroph

Answer 2

A strain that cannot synthesize a particular nutrient and needs that nutrient to be supplemented in its growth medium is called an auxotroph.

Question 3

prototroph

Answer 3

A strain that can synthesize a particular nutrient and does not need that nutrient to be supplemented in its growth medium is called an prototroph.

Question 4

transduction

Answer 4

occurs when a virus infects a bacterium and then transfers bacterial genetic material from that bacterium to another

Question 5

transformation

Answer 5

genetic material is released into the environment when a bacterial cell dies, then binds to a living bacterial cell, which can incorporate it

Question 6

F factor

Answer 6

fertility factor, a type of plasmid which allows for conjugation

strains of E. coli that contain an F factor are designated F+, while strains without F factors are termed F–

Question 7

conjugation bridge

Answer 7

pili project from F+ cells and attempt to make contact with nearby F– cells. Once contact is made, the sex pili shorten and thereby draw the donor and recipient cells closer together, and the cells form a conjugation bridge between them providing a passageway for DNA transfer

Question 8

relaxosome

Answer 8

a protein complex encoded by the F factor which first recognizes a DNA sequence in the F factor known as the origin of transfer, and cuts the DNA there. The relaxosome also catalyzes the separation of the DNA strands, and only the cut DNA strand is transferred to the recipient cell. As the DNA strands separate, most of the proteins within the relaxosome are released, but one protein, called relaxase, remains bound to the end of the cut DNA strand forming a nucleoprotein.

Question 9

nucleoprotein

Answer 9

The complex between the single-stranded DNA and relaxase is called a nucleoprotein because it contains both nucleic acid (DNA) and protein (relaxase)

Question 10

what occurs after creation of the nucleoprotein complex in conjugation?

Answer 10

DNA/relaxase complex is recognized by a coupling factor that promotes the entry of the nucleoprotein into the exporter, a complex of proteins that spans both inner and outer membranes of the donor cell (In bacterial species, this complex is formed from 10 to 15 different proteins that are encoded by genes within the F factor), travelling through the conjugation bridge and into the recipient cell

Question 11

Hfr stand for what?

Answer 11

high frequency recombination

Question 12

How are Her strains formed?

Answer 12

an F factor may align with a similar region found in the bacterial chromosome and integrate into the bacterial chromosome through recombination. Several different sites on the E. coli chromosome allow for this type of integration.

Question 13

F’ factor

Answer 13

a recombined F factor which was imprecisely excised from the host (Hfr) bacteria, and now carries a portion of the bacterial chromosome

Question 14

Elie Wollman and François Jacob’s 1950s experiment which involved interrupted mating was involved what type of gene transfer?

Answer 14

conjugation

Question 15

transmission of a F or F’ factor to a new bacterium involves what type of gene transfer?

Answer 15

conjugation

Question 16

what types of cell result from conjugation between an F- cell and a Hfr cell?

Answer 16

a F- cell and an Hfr cell

Because the recipient (F-) receives only a portion of the F plasmid, it remains an F- cell; however, it also acquires some chromosomal genes from the donor (Hfr). Recombination can integrate the donor DNA into the recipient’s chromosome . The recipient is now a recombinant F- cell that contains its own genes as well as some donor genes.

Question 17

List and describe the natural vector(s) of horizontal gene transfer in bacteria

Answer 17

Transformation: Free DNA in the environment and a competent recipient
Transduction: Bacteriophage
Conjugation: Cell-to-cell contact and F plasmid, which is either in cytosol (F+) or incorporated into chromosome of donor (Hfr) cell

Question 18

genetic maps made through conjugation experiments are measured in what units?

Answer 18

minutes, a typical E. coli cell takes about 100 minutes to be fully transferred through conjugation

Question 19

episomes

Answer 19

proposed by François Jacob and Élie Wollman in 1958 to describe extra-chromosomal genetic material that may replicate autonomously or become integrated into the chromosome

Question 20

how many bp/genes on a plasmid?

Answer 20

varies, from a few thousand base pairs and a one or two genes to 100,000-500,000 bp with dozens to hundreds of genes

Question 21

lytic cycle

Answer 21

the bacteriophage directs the synthesis of many copies of the phage genetic material and coat proteins. These components then assemble to make new phages. When synthesis and assembly are completed, the bacterial host cell is lysed (broken apart), releasing the newly made phages into the environment.

Question 22

which phage life cycle is followed by a virulent phage?

Answer 22

virulent phages follow only a lytic cycle, and thus infection results in the death of the host cell

Question 23

lysogenic cycle

Answer 23

During the lysogenic cycle, most types of phages integrate their genetic mate- rial into the chromosome of the bacterium. This integrated phage DNA is known as a prophage. A prophage can exist in a dormant state for a long time during which no new bacteriophages are made. When a bacterium containing a lysogenic prophage divides to produce two daughter cells, the prophage’s genetic material is copied along with the bacterial chromosome. Therefore, both daughter cells inherit the prophage. At some later time, a prophage may become activated to excise itself from the bacterial chromosome and enter the lytic cycle. When this happens, it promotes the syn- thesis of new phages and eventually lyses the host cell. A bacteriophage that usually exists in the lysogenic cycle is called a temperate phage. Under most conditions, temperate phages do not produce new phages and do not kill the host bacterial cell.

Question 24

temperate phage

Answer 24

A bacteriophage that usually exists in the lysogenic cycle is called a temperate phage. Under most conditions, temperate phages do not produce new phages and do not kill the host bacterial cell.

Question 25

prophage

Answer 25

During the lysogenic cycle, most types of phages integrate their genetic material into the chromosome of the bacterium. This integrated phage DNA is known as a prophage. A prophage can exist in a dormant state for a long time during which no new bacteriophages are made. When a bacterium containing a lysogenic prophage divides to produce two daughter cells, the prophage’s genetic material is copied along with the bacterial chromosome. Therefore, both daughter cells inherit the prophage.