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Chapter 7 Flashcards

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Biology 101 flashcards
1
Q

What are common allelic variations among bacteria?

A

Sensitivity to antibiotics

Differences in their nutrient requirements for growth

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2
Q

What is genetic transfer?

A

The physical transfer of genetic material from one bacterial cell to another.

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3
Q

Why is genetic transfer an advantage?

A

It enhances the genetic diversity of bacterial species.

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4
Q

What is an example of the advantage of genetic transfer?

A

A bacterial cell carrying a gene that provides antibiotic resistance may transfer this gene to another bacterial cel, allowing that bacterial cell to survive exposure.

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5
Q

What is the first mechanism for transfering genetic material?

A

Conjugation

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6
Q

What is conjugation?

A

A form of genetic transfer between bacteria that involves direct physical interaction between two bacterial cells. One bacterium acts as donor and transfers genetic material to a recipient cell.

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7
Q

What is a second mechanism of genetic transfer?

A

Transduction

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8
Q

What is transduction?

A

A form of genetic transfer between bacterial cells in which a bacteriophage transfers bacterial DNA from one bacterium to another

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9
Q

What is the third mechanism for genetic transfer?

A

Transformation

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10
Q

What is transformation?

A
  1. when a plasmid vector or segment of chromosomal DNA is introduced into a bacterial cell
  2. When a normal cell is converted into a malignant cell.
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11
Q

A form of genetic transfer that involves the uptake of a fragment of DNA from the environment is called

a. conjugation
b. transduction
c. transformation
d. all of the above.

A

c. transformation

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12
Q

Who first discovered bacteria’s transfer of genetic material? When?

A

Joshua Lederberg
Edward Tatum
1946

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13
Q

What is a minimal medium?

A

A type of growth medium for microorganisms that contains a mixture of reagents that are required for growth; nothing additional has been added.

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14
Q

What is a auxotroph?

A

A strain that cannot synthesize a particular nutriet and needs that nutrient supplemented in its growth medium or diet.

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15
Q

What is a prototroph?

A

A strain that does not need a particular nutrient supplemented in its growth medium or diet.

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16
Q

What did lederberg and Tatum study?

A

E. coli and putting bacteria in an environment which lacks the needed nutrients for half of the bacteria but, is perfect for another. They observed the transfer of genetic material.

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17
Q

Describe how gene transfer can explain the growth of colonies on the middle plate?

A

To grow, the colonies must have functional copies of all five genes. This could occur by the transfer of the met+ bio+ genes to the met- bio- thr+thi+ strain or the transfer of the thr+leu+ and thi+ genes to the met+bio+thr-leu- strains

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18
Q

In 1950, what did Bernard Davis do?

A

conducted an experiment showing that two strains of bacteria must make physical contact with each other to transfer genetic material.

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19
Q

How did Bernard David conduct his experiment?

A

Used a U-tube at the bottom is a filter with pores small enough to allow the passage of genetic material, but too small to allow bacteria cells to pass. One side was one bacterial strain with a combination of nutritional requirements, the other had a different strain requiring nutritional requirements. It showed no bacteria colonies grew on the plate, they needed direct contact to grow.

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20
Q

In Bernard Davis study, what was the purpose of using a U-Tube?

A

Because bacteria are too large to pass through the filter, the aparatus can determine if direct cell-to-cell contact is necessary for gene transfer to occur.

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21
Q

What is an F factor?

A

A fertility factor found in certain strains of bacteria in addition to their circular chromosome. Strains of bacteria that contain an F factor are designated F+; strains without F factor are F-

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22
Q

F factor carry what?

A

Several genes that are required for conjugation to occur.

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23
Q

Would a circular DNA molecule be found in an F+ or F- cell?

A

F+

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24
Q

What is sex pili?

A

A structure on the surface of bacterial cells that acts as an attachment site to promote the binding of bacteria to each other.

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25
Q

The gene encoding the pilin protein (traA) is located where?

A

On the F factor.

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26
Q

The pili act as what?

A

Attachment sites that promote the binding of bacteria to each other.

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27
Q

F+ strain makes physical contact with what strain?

A

F- strain

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28
Q

What is a conjugation bridge?

A

A connection between two bacterial cells that provides a passageway for DNA during conjugation.

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29
Q

What are the functions of relaxase, coupling factor, and the exporter?

A

Relaxase is part of the relaxsome, which is needed for the cutting of the F factor and its transfer to the recipient cell. The coupling factor guides the DNA strand to the exporter, which transports it to the recipient cell.

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30
Q

Genes within the F factor encode a protein complex called what in conjugation?

A

Relaxsome

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31
Q

What is a relaxosome?

A

A protein complex that recognizes the origin of transfer in F factors and other conjugative plasmids, cuts one DNA strand, and aids in the transfer of the T DNA.

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32
Q

The relaxosome first recognizes what in conjugation?

A

A DNA in the F factor known as the origin of transfer.

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33
Q

What is the origin of transfer?

A

The location on an F factor or within the chromosome of an Hfr strain that is the initiation site for the transfer of DNA from one bacterium to another during conjugation.

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34
Q

After the relaxosome recognizes a the origin of transfer in conjugation, what happens?

A

One DNA strand in the site is cut. The relaxosome also catalyzes the separation of the DNA strands, and only the cut DNA strand is transferred to the recipient cell.

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35
Q

What happens when the DNA strands separate in conjugation?

A

Most of the proteins within the relaxosome are released, but one protein, called relaxase, remains bound to the end of the cut DNA strand.

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36
Q

What is a nucleoprotein?

A

A complex of DNA or RNA and protein.

It is the complex between the single-stranded DNA and relaxase.

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37
Q

Why is it called nucleoprotein?

A

It contains both nucleic acid (DNA) and protein (relaxase)

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38
Q

What is the second phase of conjugation?

A

The export of the nucleoprotein complex from the donor cell to the recipient cell.

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39
Q

How does the export of the nucleoprotein complex from one cell to the other cell happen?

A

The DNA/relaxase complex is recognized by a coupling factor that promotes the entry of the nucleoprotein into the exporter.

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40
Q

What is the exporter?

A

A complex of proteins that spans both inner and outer membranes of the donor cell.
In bacteria, this complex is formed from 10-15 proteins encoded by genes within the F factor.

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41
Q

Once the DNA/relaxase complex is pumped out of the donor cell, what happens?

A

It travels through the conjugation bridge and then into the recipient cell.
The other strand of the F factor DNA remains in the donor cell, where DNA replication restores the F factor DNA to its original double-stranded condition.

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42
Q

After the recipient cell receives a single strand of the F factor DNA molecule in conjugation, what happens?

A

Relaxase catalyzes the joining of the ends of the linear DNA molecule to form a circular molecule. The single-stranded DNA is replicated in the recipient cell to become double-stranded.

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43
Q

What is the result of conjugation?

A

The recipient cell has aquired F factor and is converted to an F+ cell.

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44
Q

What is a plasmid?

A

A general name used to describe circular pieces of DNA that exist independently of the chromosomal DNA. Some plasmids are used as vectors in cloning experiments.
General name for F Factor.

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45
Q

What are episomes?

A

A segment of bacterial DNA that can exist as an F factor and also integrate into the chromosome.

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46
Q

A plasmid has its own what?

A

Origin of replication that allows it to be replicated independently of the bacterial chromosome.

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47
Q

What influences how many copies of the plasmid are found in a cell?

A

The DNA sequence of the origin of replication.

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48
Q

Why do bacteria have plasmids?

A

They are not usually necessary for bacterial survival, however, certain genes within a plasmid provide some type of growth advantage to the cell.

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49
Q

What is the first category of plasmids?

A

Fertility plasmids-F factors, allow bacteria to conjugate with each other.

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50
Q

What is the second category of plasmids?

A

Resistance plasmids-R factors: contain genes that confer resistancce against antibiotics and other types of toxins.

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51
Q

What is the Third category of plasmids?

A

Degradative plasmids: Carry genes that enable the bacterium to digest and utilize unusual substances.
Exampe: a degradative plasmid may carry genes that allow a bacterium to digest an organic solvent such as toluene

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52
Q

What is the fourth category of plasmids?

A

Col-plasmids: they contain genes that encode colicins, which are proteins that kill other bacteria.

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53
Q

What is the fifth category of plasmids?

A

Virulence plasmids: carry genes that turn a bacterium into a pathogenic strain.

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54
Q 
A bacterial cell with an F factor conjugates with an F- cell. Following conjugation, the two cells would be
a. F+
b. F-
C. one F+ and one F-
d. none of the above.
A

a. F+

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55
Q

Which of the following is a type of plasmid?

a. F factor (fertility factor)
b. R factor (resistance plasmids)
c. Virulence plasmids
d. all of the above.

A

d. all of the above.

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56
Q

Who discovered Hfr strain?

A

Luca Cavalli-Sforza

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57
Q

What is an Hfr strain?

A

A bacterial strain in which an F factor has become integrated into the bacterial chromosome. During conjugation, an Hfr strain can transfer segments of the bacterial chromosome.

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58
Q

Why is it called Hfr?

A

High frequency of recombination

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59
Q

How is an Hfr strain formed?

A

An F factor may align with a similar region found in the bacterial chromosome. Due to recombination, the F factor may integrate into the bacterial chromosome.

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60
Q

F Factros can integrate where?

A

In several different sites that are scattered around the E coli chromosome.

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61
Q

How is an F’ factor different from an F factor?

A

F’ factor carries a portion of the bacterial chromosome, whereas an F factor does not.

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62
Q

How is an Hfr strain excised from the bacterial chromosome?

A

The F factor DNA is looped out from the chromosome, which is followed by recombination that releases the F factor from the chromosome.
It is imprecise.

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63
Q

What is an F’ Factor?

A

an F factor that also carries genes derived from the bacterial chromosome.

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64
Q

What determines the starting point and direction of the transfer process of Hfr cell to an F- cell?

A

The origin of transfer within an integrated F factor.

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65
Q

What happens when one of the DNA strands is cut in Hfr cell transfer to F- cell.

A

The cut site is the starting point at which the Hfr chromosome enter the F- recipient cell.
From this starting point, one strand of DNA from the Hfr chromosome begins to enter the F- cell in a linear manner.
The transfer process occurs in conjugation with chromosomal replication, so the Hfr cell retains its original chromosomal composition.

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66
Q

How long is the entire Hfr chromosome transffer?

A

1.5 to 2 hours.

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67
Q

Why is only a portion of the Hfr chromosome transmitted to the F- cell?

A

Because most conjugations do not last 1.5 to 2 hours

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68
Q

Once the chromosomal material from the Hfr cell is inside the F- cell, what happens?

A

The material can swap or recombine, with the homologous region of the recipient cell’s chromosome.

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69
Q

How does the recombination affect the recipient cell?

A

It may provide the recipient cell with a new combination of alleles.

70
Q

What is an important feature of Hfr conjugation?

A

The bacterial chromosome is transferred linearly to the recipient strain. So, some genes will be transferred first and other later.

71
Q

In any particular Hfr strain, the origin of transfer has a specific orientation that promotes what?

A

Either a counterclockwise or clockwise transfer of genes.

72
Q

Who carried out the genetic mapping experiments in bacteria and when?

A

Elie Wollman
Francois Jacob
1950

73
Q

What did Wollman and Jacob’s experiment consist of?

A

Bacteriophages can be sheared from the surface of E coli cells if they are spun in a blender.
This shortens the time of conjugation, so they are able to determine the order of the genes in the chromosomes.

74
Q

What is interrupted mating?

A

A method used in conjugation experiments in which the length of time that the bacteria spend conjugating is stopped by a blender treatment or other type of harsh agitation.

75
Q

Researchers scale genetic maps from bacterial conjugation studies in units of what?

A

Minutes which refers to the relative time it takes for genes to first enter an F- recipient strain during a conjugation experiment.

76
Q

How is the distance between two genes determined for bacterial genetic maps?

A

By comparing their times of entry during a conjugation experiement.

77
Q

With regard to conjugation, a key difference between F+ and Hfr cells is that an Hfr cell

a. is unable to conjugate
b. transfers a plasmid to the recipient cell.
c. transfers a portion of the bacterial chromosome to the recipient cell.
d. becomes an F- cell after conjugation.

A

c. transfers a portion of the bacterial chromosome to the recipient cell.

78
Q

In mapping experiments, ______________ strains are conjugated to F- strains. The distance between two genes is determined by comparing their _________ during a conjugation experiment.

a. F+, times of entry
b. Hfr, times of entry
c. F+, expression levels.
d. Hfr, expression leveles.

A

b. Hfr, times of entry

79
Q

What is lysis?

A

Following infection of the cell, new viral particles are made, which are then released from the cell.

80
Q

Bacteriophages are composed of what?

A

genetic material that is surrounded by a protein coat.

81
Q

Some bacteriophages do what?

A

Bind to the surface of a bacterium and inject their genetic material into the bacterial cytoplasm.

82
Q

What determines whether a phage follows a lytic cycle or a lysogenic cycle?

A

The specific type of virus and its growth conditions.

83
Q

What is a lytic cycle?

A

A type of growth cycle for a phage in which the phage 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 is completed, the bacterial host cell is lysed, and the newly made phages are released into the environment.

84
Q

What are examples of phages that can transfer bacterial chromosomal DNA from one bacterium to another?

A

P22 and P1 phages, which infect the bacterial species

Salmonella typhimurium and E coli

85
Q

How does a bacteriophage transfer bacterial chromosomal genes from one cell to another?

A

When a phage infects a bacterial cell and follows the lytic cycle, the bacterial chromosome is digested into fragments of DNA. The phage DNA directs the synthesis of more phage DNA and proteins, which then assemble to make new phages. Occasionally a mistake happsns where a fragment of Bacterial DNA assembles with the phage proteins. When lysed this bacterial DNA on the phage can bind to another bacterium and recombine the DNA.

86
Q

Transduction is sometimes described as a mistake in the bacteriophage reproductive cycle. Explain.

A

The normal process is for bacteriophage DNA to be incorporated into a phage coat. In transduction, a segment of bacterial chromosomal DNA is incorporated into a phage coat

87
Q

Can transduction be used to map the distance between bacterial genes?

A

Yes, but only if the genes are relatively close together.

88
Q

P1 phages cannot package gene pieces that are greater than what percent of the entire E. coli chromosome?

A

2 to 2.5%

89
Q

P22 phages cannot package gene pieces that are greather than what percent of the entire S. typhimurium chromosome.

A

1%

90
Q

What is cotransduction?

A

The phenomenon in which a bacteriophage transfers a piece of DNA carrying two closely linked genes.

91
Q

The likelihood that two genes will be cotransduced depends on what?

A

How close together they lie.

92
Q

In genetic mapping, what is used to determine the order and distance between genes that lie fairly close together in bacteria?

A

Cotransduction

93
Q

If the genes were very far apart on the bacterial chromosome, how would the cotransduction results be different?

A

The genes would never be cotransduced

94
Q

What is the equation that relates cotransduction frequency with map distance obtained from conjugation?

A

Cotranduction frequency= (1-d/L)^3

95
Q

What do the letters represent in the cotransduction frequency equation?

A

Cotranduction frequency= (1-d/L)^3
d: distance between two genes in minutes
L= size of the chromosomal pieces (in minutes) that the phage carries during transduction (for p1 transduction, the size is approximately 2% which equals 2 minutes.)

96
Q

What does the cotransduction frequency equation assume?

A

That the bacteriophage randomly packages pieces of the bacterial chromosome that are similar in size.

97
Q

Is the assumption for using the cotransduction frequency equation always valid?

A

No, it depends on the type of phage.

98
Q

During transduction via P1,

a. any small fragment of the bacterial chromosome may be transferred to another bacterium by a bacteriophage.
b. only a specific fragment of DNA may be transferred to another bacterium by a bacteriophage.
c. any small fragment of DNA may be transferred during conjugation
d. only a specific fragment of DNA may be transferred during conjugation.

A

a. any small fragment of the bacterial chromosome may be transferred to another bacterium by a bacteriophage.

99
Q

Cotransduction may be used to map bacterial genes that are

a. far apart
b. close together on the bacterial chromosome
c. both a and b
d. neither a or b

A

b. close together on the bacterial chromosome

100
Q

Who discovered transformation? When?

A

Frederick Griffith

1928

101
Q

What happens during transformation?

A

A living bacterial cell takes up DNA that was released from a dead bacterium. This DNA may then recombine into the living bacterium’s chromosome, producing a bacterium with genetic material that it has received from the dead bacterium.

102
Q

What is natural transformation?

A

A natural process of transformation that occurs in certain strains of bacteria.

103
Q

What are competent cells?

A

Cells that can be transformed by extracellular DNA

104
Q

What is competence factors?

A

Proteins that are needed for bacterial cells to become naturally transformed by extracellular DNA.

105
Q

The competence factors facilitate what?

A

The binding of the DNA fragments to the cell surface, the uptake of DNA into the cytoplasm, and its subsequent incorporation into the bacterial chromosome.

106
Q

What can affect whether a bacterium is competent to take up genetic material from its environment?

A

Temperature
Ionic conditions
Nutrient availability

107
Q

What is the first step of transformation?

A

First, a large fragment of genetic material binds to the surface of the cell.
Competent cells express DNA receptors that promote the binding.
The large piece of chromosomal DNA is cut to smaller fragments by an extracellular bacterial enzyme known as endonuclease.
The DNA fragments are double-stranded during this stage.

108
Q

What’s the second step of transformation?

A

The DNA fragment begins its entry into the bacterial cytoplasm. For this to occur, the double-stranded DNA interacts with proteins in the bacterial membrane. One of the DNA strands is degraded, and the other strand enters the bacterial cytoplasm via an uptake system which is similar to conjugation, but involves the DNA uptake rather than export.

109
Q

To be stably inherited, what must happen to the DNA strand in Transformation?

A

It must be incorporated into the bacterial chromosome.

110
Q

What is homologous recombination?

A

The exchange of DNA segments between homologous chromosomes.

111
Q

What must happens for homologous recombination to occur?

A

The single-stranded DNA aligns itself with the homologous location on the bacterial chromosome.

112
Q

What is a heteroduplex?

A

A double-stranded region of DNA that contains one or more base mismatches.

113
Q

Are heteroduplexes permanent in transformation?

A

no

114
Q

Why are heteroduplexes not permanent in transformation?

A

DNA repair enzymes in the recipient cell recognize it and repair it.

115
Q

What is nonhomologous recombination?

A

The exchange of DNA between nonhomologous segments of chromosomes or plasmids.

116
Q

What’s another name for nonhomologous recombination?

A

illegitimate recombination

117
Q

What is cotransformation?

A

The phenomenon in which bacterial transformation transfers a piece of DNA carrying two closely linked genes.

118
Q

When is cotransformation frequency high and low?

A

It’s high when genes are close togehter

Low when they are far apart.

119
Q

Transformation is also a common lab method to do what?

A

Get plasmid DNA into cells.

120
Q

What is artificial Transformation?

A

Transformation of bacteria that occurs via experimental treatments.

121
Q

What is one way to cause artificial transformation?

A

Treat the cells with calcium chloride, which is followed by a brief period of high temperature. These conditions make the cells permeable to small DNA molecules.

122
Q

What is another method for artificial transformation?

A

Electroporation,

Makes cells permeable to DNA by using an externally applied electric field.

123
Q

What is the competence-stimulating peptide (CSP)

A

a peptide secreted by certain species of bacteria that allows them to become competent for transformation.

124
Q

Why are S. pneuomoniae cells more likely to take up DNA from nearby S. pneumoniae cells that have died and released their DNA into the environment?

A

Because competence requires a high external concentration of CSP.

125
Q

Other bacterial species promote the uptake of DNA among members of their own species via what?

A

DNA uptake signal sequence.

126
Q

What is DNA uptake signal sequences?

A

DNA sequences found in certain speices of bacteria that are needed for a DNA fragment to be taken up during transformation.

127
Q

From the following list, what is the correct order for the steps of transfromation?

  1. recombination with the bacterial chromosome.
  2. Binding of a larage DNA fragment to the surface of a bacterial cell.
  3. cutting a large DNA fragment into smaller pieces.
  4. uptake of DNA into the cytoplasm
  5. degradation of one of the DNA strands.
    a. 1, 2, 3, 4, 5,
    b. 2, 3, 5, 4, 1
    c. 2, 3, 4, 5, 1
    d. 2, 5, 4, 3, 1
A

b. 2, 3, 5, 4, 1

128
Q

Some bacterial species preferentially take up DNA fragments from members of their own speices. This can occur via

a. competence-stimulating peptide (CSP)
b. DNA uptake signal sequences
c. both a and b
d. none of the above.

A

c. both a and b

129
Q

What is horizontal gene transfer?

A

The transfer of genes from one individual to another individual that is not its offspring.

130
Q

What are examples of horizontal gene transfer?

A

Conjugation
Transformation
Transduction

131
Q

Why is horizontal gene transfer important?

A

Its medical relevance and antibiotic resistance

132
Q

What is acquired antibiotic resistance?

A

The acquisition of antibiotic resistance because a bacterium has taken up a gene or plasmid from another bacterial strain.

133
Q

Which of the following is an example of horizontal gene transfer?

a. the transfer of a gene from one strain of E. coli to a different strain via conjugation
b. The transfer of a gene from one strain of E. coli to a different strain via transduction.
c. the transfer of an antibiotic resistance gene from E. coli to salmonella typhimurium via transformation
d. all of the above.

A

d. all of the above.

134
Q

Do scienties consider viruses to be living entities? Why?

A

No, because they rely on a host cell for their existence and proliferation.

135
Q

Can viruses have traits?

A

Yes, because they have unique biological structures and functions.

136
Q

What is T4?

A

A bacteriophage virus that infects E coli.

137
Q

How many different proteins bind together to form a tail fiber in T4?

A

five

138
Q

Where is the genetic material located that determine the structure of the bacteriophage?

A

Inside the virus itself.

139
Q

As bacteriophages progress through the lytic cycle, what do they produce?

A

New phages which are released when the bacterial cell lyses

140
Q

What is a plaque?

A

A clear zone within a bacterial lawn on a petri plate. It is due to repeated cycles of viral infection and bacterial lysis.

141
Q

Over time, the plaques become larger in diameter. Explain why?

A

As more viruses are made, they are released from host cells and eventually cause neighboring cells to lyse. This makes the plaque grow larger.

142
Q

What can be considered a trait of the bacteriophage?

A

The morphology of plaques

143
Q

Why is the morphology of plaques a trait?

A

Because some mutations in the bacteriophage’s genetic material alter the ability of the phage to form plaques

144
Q

What was Seymour Benzer’s experiment?

A

He tested the mutations of genes by study plaques in different strains of E. Coli.

145
Q

If you want to see if the mutation are in the same genes, what test can be performed?

A

Complementation test.

146
Q

What is complementation?

A

A phenomenon in which the presence of two different mutant alleles in the same organism produces a wild-type phenotype. It usually happens because the two mutations are in different genes, so the organism carries one copy of each mutant allele and one copy of each wild-type allele.

147
Q

With regard to the locations of mutations, explain the difference between noncomplementation and complementation?

A

Noncomplementation indicates that two mutations are in different genes, whereas complementation indicates that the two mutations are in the same genes.

148
Q

What is noncomplementation?

A

The phenomenon in which two mutant alleles in the same organism do no produce a wild-type phenotype.

149
Q

What is cistron?

A

The smallest genetic unit that produces a positive results in a complementation experiment. A cistron is equivalent to a gene.

150
Q

A bacterial plaque is

a. a clear region in a bacterial lawn where the bacteria have been lysed.
b. a bacterial cell that has a phage attached to its surface.
c. a dense region of bacterial growth
d. none of the above.

A

a. a clear region in a bacterial lawn where the bacteria have been lysed.

151
Q

When two different alleles that affect the same trait exhibit complementation, an interpretation is that

a. the alleles occur in the same genes
b. the alleles occur in two different genes.
c. both alleles are dominant
d. one allele is dominant and the other is recessive.

A

b. the alleles occur in two different genes.

152
Q

What is intragenic mapping?

A

Mapping which seeks to establish distances between two or more mutations within the same genes.

153
Q

What is intergenic mapping?

A

The determination of the distances between two different genes.

154
Q

Benzer’s results showed what?

A

Rather than being an indivisible particle, a gene must be composed of a large structure that can be subdivided during intragenic crossing over.

155
Q

Can two noncomplementing strains of viruses produce an occasional plaque?

A

at a very low rate

156
Q

How can noncomplementing strains of viruses produce an occasional plaque?

A

If intragenic recombination has taken place.

157
Q

How does intragenic recombination occur?

A

A crossover may occur in the very short region between each mutation. The crossover produces a double-mutant gene A and a wild-type gene A. Thus plaque can form.

158
Q

What is the general strategy for intragenic mapping?

A

Two different noncomplementing phage mutants are mixed together in equal numbers then coinfected into E. coli.
When two different mutants coinfect the same cell, intragenic recombination can occcur producing wild type phages and mutant phages.
Following coinfection and lysis of E coli, a new population of phages is isolated, which is expected to contain predominantly nonrecombinant phages.

159
Q

How can the frequency of recombinant phages be determined?

A

By comparing the number of wild-type phages, produced by intragenic recombination, and the total number of phages.

160
Q

What equation can be used to determine the frequency of recombinants when dealing with intragenic recombination?

A

Frequency of recombinants= 2[ Wild-type plaques obtained in E. coli]/ Total number of plaques obtained in E. coli.

161
Q

The goal of intragenic mapping is to determine the

a. order and distance between different genes.
b. order and distance between mutations in a single gene.
c. locations of genes within a viral genome.
d. insertion site of a viral genome into the host cell’s chromosome.

A

b. order and distance between mutations in a single gene.

162
Q

Conjugation is somtimes called “bacterial mating.” is it a form of sexual reproduction?

A

No, but it is similar to sexual reproduction in the sense that the genetic material from two cells are somewhat mixed. In conjugation, there is not the mixing of two genomes, one from each gamete. Instead, genetic material from one cell is transferred to another. This transfer can alter the combination of genetic traits in the recipient cell.

163
Q

What is the difference between an F+ and an Hfr strain? Which type of strain do you expect to transfer many bacterial genes to recipient cells?

A

An F+ strain contains a separate, circular piece of DNA that has its own origin of transfer. An Hfr strain has its origin of transfer integrated into the bacterial chromosome. An F+ strain can transfer only the DNA contained on the F factor. If given enough time, an Hfr strain can actually transfer the entire bacterial chromosome to the recipient cell.

164
Q

What is the role of sex pili during conjugation?

A

They promote the binding of donor and recipient cells.

165
Q

What is cotransduction? What determines the liklihood that two genes will be cotransduced?

A

It is the transduction of two or more genes. The distance between the genes determines the frequency of cotransduction. When two genes are close together, the cotransduction frequency is high compared to if they are far apart.

166
Q

Host DNA is hydrolyzed into small pieces, which are occasionally assmebled with phage proteins, creating a phage with bacterial chromosomal DNA. If the breakage of the chromosomal DNA is not random, how might nonrandom breakage affect cotransduction frequency?

A

If a site that frequently incurred a breakpoint was between two genes, the cotransduction frequency of these tow genes would be much less, because the site where the breakage occurred would separate the two genes from each other.

167
Q

Which bacterial genetic transfer process does not require recombination with the bacterial chromosome?

A

The transfer of conjugative plasmids such as F factor DNA.

168
Q

Intragenic mapping is sometimes called interallelic mapping. Explain why the two terms mean the same thing.

A

Allele is an alternative form of a gene. Therefore, mutations in the same gene among different phages are alleles of each other; mutations may be at different positions within the same gene. When we map the distance between mutation in the same gene, we are mapping the distance between the mutations that create different alleles of the same gene. An intragenic map describes the locations of mutations within the same gene.

169
Q

What is an interrupted mating experiment? What type of experimental information can be obtained from this type of study? Why is it necessary to interrupt mating?

A

It’s a procedure in which two bacterial strains are allowed to mate, and then the mating is interrupted at various time points. The interruption occurs by agitation of the solution in which the bacteria are found. This type of study is used to map the locations of genes. It is necessary to interrupt mating so that you can vary the time and obtain information about the order of transfer;; which gene transferred first, second…

170
Q

In an experiment involving P1 transduction, the cotranduction frequency was .53. How far apart are the two genes?

A

Cotransduction frequency= (1- d/L)^3
.53= (1 - d/2 minutes)^3
d= 0.38 minutes

Genetics (11 decks)

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