Chapter 6/10

Question 1

Lateral Gene Transfer

Answer 1

the transfer of genetic material from one organism to another that is not one of its offspring

• horizontal gene transfer= from one organism to another of different type
• vertical gene transfer=parent to child organism

Question 2

Genetic Recombination

Answer 2

the physical exchange of DNA between genetic elements, from donor strand to host genome

Question 3

3 kinds of Lateral Gene Transfer

Answer 3

1. Transformation
2. Transduction
3. Conjugation

Question 4

Transformation

Answer 4

uptake of name DNA
-Discovered by Fredrick Griffith in the late 1920s working with Streptococcus pneumoniae, setting the stage for the discovery of DNA

Question 5

Fredrick Griffith’s Experiment

Answer 5

• Concluded something was being exchanged from heat killed bacteria to live bacteria
• View slides on rough/smooth strain bacterial experiment*

Question 6

Competent Cells

Answer 6

• cells capable of taking up DNA and being transformed
• In naturally transformable bacteria, it is highly regulated
• in other strains, specific procedures are necessary to make cells competent
• Electricity can be used to force cells to take up DNA (electroportation)

Question 7

Factors promoting Transformation

Answer 7

1. Uptake mechanisms and rate
2. quantity and environmental DNA
3. Longevity of environmental DNA
4. usefulness and incomparability of DNA
5. Various inhibitors (vesicle packaging, digestion, free floating)
   * all these factors affect how often it occurs

Question 8

Transduction

Answer 8

• Gene transfer by viruses
• Bacteriophages= viruses that infect bacteria
• viruses very good at transfer DNA from one organism to another, but can mess up and cause horizontal gene transfer; 2 ways

Question 9

Generalized transduction

Answer 9

ANYWHERE
DNA from any portion of host genome packaged inside virus
-defective virus particle incorporates fragment of cell’s chromosome randomly
-no longer carrying viral DNA, just transferring part of host genome
-low efficiency: random when it occurs and what part of the DNA is included in the virus

Question 10

Specialized transduction

Answer 10

DNA from a specific region integrated directly into virus genome
ONLY WHERE VIRUS IS
-DNA of temperate virus excises incorrectly and either takes too much host DNA or not enough host DNA
~OCCURS MORE OFTEN
-efficiency high

Question 11

Conjugation

Answer 11

*“bacterial sex”
-mechanism of genetic transfer that involves cell-to-cell contact
~Plasmid-encoded mechanism
~Donor cell: contains conjugative plasmid
~Recipient cell: does NOT contain plasmid

Question 12

F (fertility) plasmid

Answer 12

• Needed in conjugation
• Circular DNA molecule, ~100kbp that contains genes that regulate DNA replication
• Contains severe transposable elements that allow plasmid to integrate into host chromosome
• Contain tra genes that encode transfer functions
• after conjugation, both cells contain plasmid and are F+ cells

Question 13

Sex pilus

Answer 13

• Essential for conjugation
• only produced by donor cell and used to draw adjacent cells in for mating
• have to have F+ and F- cells for conjugation to occur (can’t have two F+ mating)

Question 14

Rolling circle replication

Answer 14

DNA synthesis in necessary for DNA transfer by conjugation

-also used by some viruses

Question 15

Hfr cell

Answer 15

plasmid is separate from chromosome

• cells possessing integrated F plasmid
• high rates of recombiination

Question 16

episome

Answer 16

when F plasmid is part of host chromosome

Question 17

Presence of F plasmid

Answer 17

results in:

1. ability to synthesize F pills
2. Mobilization of DNA for transfer
3. Alteration of surface receptors so cell can no longer act as recipient

Question 18

Insertion sequences

Answer 18

mobile elements present in both the F plasmid and E. coli chromosome facilitating homologous recombination

• plasmid is now part of chromosome, transferring chromosomal genes with plasmid
• when chromosome transferred it is transferred from the middle and in order to transfer entire conjugated plasmid it has to go through the entire chromosome: often times this doesn’t happen fully

Question 19

Hfr cells: multiple insertion sequences

Answer 19

allowing it to be incorporated into the host genome in multiple places

Question 20

genetic mapping

Answer 20

genetic crosses with Hfr strains can be used to map order of genes on chromosome
-roughly takes 100 minutes to conjugate entire E. coli genome

Question 21

Identification of recombinant strains

Answer 21

requires conditions in which recombinants can grow but parents can not

• plate on 2 different media:
  1. minimal with streptomycin and glucose; selects for markers Thr+, Leu+, does not select for Lac
  2. minimal with streptomycin, lactose, threonine, leucine; selects for marker Lac+, does not select for Thr or Leu

Question 22

F’ Plasmid

Answer 22

previously integrated F plasmids that have excised and captured some chromosomal genes

Question 23

Merodiploid/ Partial diploid

Answer 23

bacterial stain that carries two copies of any particular chromosomal segment

Question 24

Complementation

Answer 24

process by which a functional copy of a gene compensates for a defective copy
-have one functional gene on two different locations

Question 25

Complementation Tests

Answer 25

determines if 2 mutations in same or different genes -necessary when different mutations in same pathway yield the same phenotype -different genes: trans configuration ~can be effective pathway (+) -same gene: cis configuration ~defective and left with defective pathway (-)

Question 26

What would be the mechanism that would most likely be the cause of a LGT event between a Bacteria and an Archaea?

Answer 26

Transformation: can take in any type of DNA * one exception: the pathway used a little different, the more similar your genes are the more likely you are to have recombination event * Most likely way of lateral gene transfer

Question 27

Gene Transfer: Archaea

Answer 27

- contain single circular chromosome - need to be grown in extreme conditions - most antibiotics do not affect them - examples of transformation, transduction, and conjugation exist, transduction works especially well with halophiles