chapter 6 part 2

Question 1

when does transformation occur

Answer 1

when a recipient cell takes up a fragment of donor DNA from the surrounding growth medium

Question 2

what is transformation used for?

Answer 2

the introduce DNA in the lab to microbial cells, plant cells, & animal cells
-it is naturally occuring mechanism than can be used to produce accurate maps of bacterial genes

mapping genes that are closely linked

Question 3

how long is transforming DNA typically?

Answer 3

usually shorter than 100 kb

Question 4

cotransformation

Answer 4

simultaneous transformation of two or more genes

Question 5

what is transformation preceded by in natural transformation?

Answer 5

lysis (the breakage of a donor cell)

Question 6

what is the passage of DNA into a recipient accompanied by in natural transformation?

Answer 6

degradation of one of the strands & the remaining strand aligns with complementary regions of the recipient chromosomes

Question 7

what does the alignment of donor & recipient DNA trigger in transformation?

Answer 7

excision of one strand of recipient DNA & replacement with donor DNA, forming a heteroduplex

Question 8

what is the daughter cell that is transformed called & what does the other daughter cell do?

Answer 8

transformant
the other daughter cell retains the recipient chromosome original DNA strand & so is unchanged

Question 9

how many steps is the lytic cycle?

Answer 9

6

Question 10

describe the lytic cycle

Answer 10

1. attachment of the phage to the host cell
2. injection of the phage chromosome into the host followed by circularization of the phage chromosome
3. replication of phage DNA using host proteins & enzymes
4. transcription & translation of phage genes
5. packaging of phage chromosomes into phage heads
6. lysis of the host cell, & release of progeny phage particles

Question 11

temperate phages

Answer 11

they have an alternate, temporary life cycle involving integration of the phage chromosome into the bacterial chromosome (lysogeny /l ytic cycle)

Question 12

lysogenic cycle

Answer 12

1. attachment & injection are the same as the lytic cycle
2. integration of the phage chromosome into the host chromosome via recombination at a specific DNA sequence found in both chromosomes
3. excision of the prophage in response to an environmental signal, through a reversal of the site-specific recombination leading to integration
4. resumption of the lytic cycle, beginning with the phage-chromosome replication

Question 13

when is the phage chromosome called the prophage?

Answer 13

once the phage is integrated into the host chromosome

Question 14

transduction

Answer 14

the transfer of genetic material from a donor to a recipient cell by way of a bacteriophage

Question 15

what are bacteriophage consisted of?

Answer 15

composed of an icosahedral head, hollow protein sheath, & sometimes a set of tail fibers

Question 16

what is bacterial transduction mediated by?

Answer 16

bacteriophages
the bacteriophage injects a donor cell & some progeny phages accidentally incorporate a fragment of donor DNA rather than a copy of the phage chromosome
-these progeny phages then infect a recipient cell & inject the donor DNA (phage doesnt enter the cell)

Question 17

what are the two types of transduction?

Answer 17

generalized transduction
specialized transduction

Question 18

the conditions leading to transduction are due to …..

Answer 18

rare errors in packaging of phage DNA during the lytic cycle

Question 19

what leads to production of a transductant bacterial strain?

Answer 19

the transfer of genetic material from a donor bacterium to a recipient via a phage

Question 20

generalized transduction

Answer 20

the transfer of RANDOM bacterial genes, is carried out by bacteriophages that cannot distinguish between phage & bacterial DNA during packing of DNA into new phage particles

Question 21

specialized transduction

Answer 21

carried out only by temperate phages & the only genes transferred are those close to the integration site

Question 22

generalized transduction steps

Answer 22

1. A normal P1 phage attaches to a donor bacterium and injects its DNA.
2. The phage’s DNA is copied, and proteins are made.
3. New phages are put together, but some (called generalized transducing phages) end up with a piece of the host’s DNA instead of their own DNA. This happens randomly based on size.
   4.The host cell bursts, releasing all the new phages.
4. The generalized transducing phages attach to new recipient cells and inject their DNA.
5. Inside the recipient, the donor DNA can combine with the recipient’s chromosome. (homologous recombination)
6. This process creates a stable transductant strain.

Question 23

in specialized transduction, what integrates into host chromosomes at specific sites?

Answer 23

temperate phages, such as lambda phage

Question 24

att site

Answer 24

the integration site in the bacterial host chromosome
-the same 15 bp sequence

Question 25

attp

Answer 25

integration site in lambda phage

Question 26

attB

Answer 26

integration site in the e. coli host

Question 27

why is the excision of the prophase usually the exact reversal of the integration?

Answer 27

because the attB & attP sites are identical

Question 28

lateral gene transfer

Answer 28

the transfer of genetic material between individual bacteria or archaea & other organisms

Question 29

what percent of genes in a genome are the result of LGT?

Answer 29

12%

Question 30

what does LGT stand for

Answer 30

lateral gene transfer

Question 31

what are the common characteristics of LGT genomic islands

Answer 31

-the group of genes in the island are like genes of distantly related species -island region has a ratio of A-T/G-C different than the rest of the genome

Question 32

genomic islands

Answer 32

area of LGT that is uniquely different than the rest of the genome

Question 33

how big are genomic islands?

Answer 33

large (10-200kb)

Question 34

how many genes do genomic islands contain?

Answer 34

multiple genes

Question 35

what can LGT in bacteria lead to?

Answer 35

acquired pathogenicity islands -promote host invasion & genes that produce toxic compounds

Question 36

ex of pathogenicity islands

Answer 36

strains of e.coli have acquired pathogenicity islands that can cause diarrhea & meningitis

Question 37

what does the aberrant excision produce in specialized transduction

Answer 37

specialized transducing phage

Question 38

what includes the galK gene

Answer 38

lambdadgal+ specialized transducing phage -can infect host but lacks genes needed to complete either lysis or lysogeny

Question 39

what includes the bioA gene?

Answer 39

lambdadbio+ specialized transducing phage -can induce lysis but lacks the genes needed for lysogeny

Question 40

merozygote

Answer 40

a state when a partially diploid bacterial cell is produced

Question 41

what can partial diploids be used for?

Answer 41

used to examine the mode of action of bacterial genes, & their regulation

Question 42

what is called a partial diploid?

Answer 42

exconjugants that contain a complete F' factor -since they contain two copies of the bacterial chromosome genes found on the F' factor

Question 43

F' cells

Answer 43

F' factor containing all its own DNA plus a segment of the bacterial chromosome which comes from aberrant excision of the F factor from an Hfr chromosome

Question 44

is complete transfer of bacterial chromosome accomplished in Hfr gene transfer?

Answer 44

no, it is too long

Question 45

can linear DNA in the recipient cell re-circularize

Answer 45

no

Question 46

what does Hfr stand for

Answer 46

high frequency recombination