Chapter 8

Question 1

Advantages of using bacteria and viruses for genetic studies

Answer 1

1. reproduction is rapid
2. many progeny are produced
3. the haploid genome allows all mutations to be expressed directly
4. asexual reproduction simplifies the isolation of genetically pure strains
5. growth in the laboratory is easy and requires little space
6. genomes are small
7. techniques are available for isolating and manipulating the genes
8. they have medical importance
9. they can be genetically engineered to produce substances of commercial value

Question 2

What bacteria is known as the workhorse

Answer 2

• Escherichia coli

Question 3

Prototroph

Answer 3

• wild type bacteria that can synthesize all compounded needed for growth from simple ingredients

Question 4

Auxotroph

Answer 4

• mutant strain that lacks one or more enzymes required for metabolizing nutrients
• will grow on supplemented media

Question 5

Plasmids are ______ DNAs

Answer 5

• extrachromosomal

- replicates independently of chromosome

Question 6

________ found that genetic exchange requires direct contact between bacterial cells by mixing two auxotrophic strains and observing that the bacteria could not pass through a filter

Answer 6

• Lederberg and Tatum

Question 7

How did the genetic exchange in Lederberg and Tatums experiment take place?

Answer 7

• the filter did not allow bacteria to pass through
• this drew them to their conclusion that genetic exchange requires direct contact between bacterial cells
• generalized transduction experiment

Question 8

Conjugation

Answer 8

• can transfer F factor
• direct transfer of DNA from one bacterium to another (donor and recipient only)
• one strand on DNA on F factor is nicked, replication occurs replacing the nicked strand

Question 9

Hfr cells (high frequency) role in conjugation

Answer 9

• F is integrated into the bacterial chromosome
• Hfr cells behave like F+ forming pili and conjugating with F-
• because F factor is in the chromosome some of chromosome is pulled into the recipient cell (F factor plus some bacterial genes results)
• remains F- bc does not get whole F factor
• amount depends on length of time of conjugation

Question 10

F+ cells vs F- cells

Answer 10

• F+ cells are donor bacterium

- F- cells are recipient bacterium

Question 11

F’ cells

Answer 11

• cells with F plasmid that contain some bacterial genes

- acts as a donor

Question 12

Merozygote

Answer 12

• bacteria that is now partially diploid

- the F factor is excised from Hfr- and some genomic genes on the episome

Question 13

Results of conjugation between cells with different F factors

Answer 13

1. F+ x F- = two F+ cells
2. Hfr x F- = one Hfr cell and one F- (no change)
3. F’ x F- = two F’ cells

Question 14

_______ found that gene mapping was interrupted by conjugation

Answer 14

• Francois Jacob and Elie Wollman

Question 15

Gene transfer differs in bacteria than eukaryotes because

Answer 15

1. DNA exchange and reproduction are NOT coupled in bacteria

2. Cell remains haploid

Question 16

Transformation

Answer 16

• DNA take up the medium

Question 17

Transduction

Answer 17

• Bacterial viruses (Phages) carry DNA from one bacterium to another

Question 18

Steps in gene transfer of bacterium and ways to map

Answer 18

1. Interrupted Conjugation
2. Transformation
3. Transduction

Question 19

What is used to map in gene transfer?

Answer 19

• the transfer times indicate the order and relative distances between genes and can be used to construct a map

Question 20

How do the different Hfr strains affect the F factor in mapping?

Answer 20

• different Hfr strains have the F factor integrated at different sites and in different orientations

Question 21

Bacterial transformation

Answer 21

• DNA is external and then taken into the cell
• the DNA is taken up from surrounding and incorporated into the genome
• can occur naturally, DNA from dead cells in the environment

Question 22

Competent cells

Answer 22

• cells that can take up DNA

Question 23

What is a major key to modern molecular biology?

Answer 23

• introduction of artificial plasmids

Question 24

Gene mapping using transformation

Answer 24

• rate of cotransformation is inversely proportional to distances between genes
  aka the faster the further apart

Question 25

Virsuses

Answer 25

• all organisms are infected by them
• nucleic acid coated in proteins
• linear or circular genomes

Question 26

Bacteriophages (phage)

Answer 26

• have two alternative life cycles

Question 27

Virulent Phage

Answer 27

• reproduce only through lytic cycle

Question 28

Temperate Phage

Answer 28

• use either lytic cycle or lysogenic cycle

Question 29

Transducing Phage

Answer 29

1. requires that the phage degrade bacteria chromosome
2. packaging DNA into phage can not be specific for phage DNA
3. recombination must occur within recipient chromosome

Question 30

Mapping genes using generalized transduction

Answer 30

• rate of cotransduction is inversely proportional to distances between genes

Question 31

Lytic Cycle

Answer 31

• Lysis the cell to spread its viral DNA

Question 32

Lysogenic Cycle

Answer 32

• Becomes a part of the plasmid for a cell and duplicates with the newly introduced virus

Question 33

Plaque

Answer 33

• Where a colony used to be but was killed off by a virus (clear areas)

Question 34

_________ studied phage recombination using the T2 bacteriophage

Answer 34

• Alfred Hershey and Raquel Rotman

Question 35

Alfred Hershey and Raquel Rotman conlcusions

Answer 35

• one strain could infect type B E.coli but not type B/2 (h+)
• also produced abnormal plaques (r-)
• allowed for the genotypes to be calculated

Question 36

Mixed infection experiment

Answer 36

• Allowed both viruses to infect a cell then observed the results