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genetics > chapter 6 part 2 > Flashcards

chapter 6 part 2 Flashcards

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Biology 101 flashcards
1
Q

transformation

A

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

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2
Q

is transformation naturally occurring or induced in a laboratory

A

both

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3
Q

how is transformation used in the laboratory

A

to introduce DNA into microbial cells, plant cells, and animal cells

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4
Q

length of transforming DNA

A

usually shorter than 100 kb
- in E. coli can contain up to 50 genes, representing at most only 1-2% of total genome of recipient

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5
Q

what is transformation useful for

A

mapping genes that are closely linked

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6
Q

cotransformation

A

simultaneous transformation of two or more genes

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7
Q

what precedes natural transformation

A

lysis

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8
Q

lysis

A

breakage of a donor cell and fragmentation of the DNA of the donor

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9
Q

how many steps in transformation

A

4

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10
Q

steps in natural transformation

A
  • lysis
  • passage of DNA into a recipient accompanied by degradation of one of the strands
  • remaining strand aligns with complementary regions of the recipient chromosome
  • alignment of donor/recipient DNA triggers excision of one strand of recipient DNA and replacement with donor DNA
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11
Q

heteroduplex

A

when alignment of donor/recipient DNA triggers excision of one strand of recipient DNA and replacement with donor DNA

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12
Q

products of transformation

A
  • one daughter cell is transformed cell (transformant)
  • other daughter cell retains the recipient chromosome original DNA strand (unchanged)
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13
Q

transformant

A

transformed cell

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14
Q

steps of lytic cycle

A
  1. attachment of phage to 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 and enzymes
  4. transcription/translation of phage genes, production of phage components
  5. packaging of phage chromosomes into phage heads
  6. lysis of host cell, release of progeny phage particles
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15
Q

temperate phages

A

have alternate, temporary life cycle involving integration of the page chromosome into the bacterial chromosome

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16
Q

does the lysogenic or lytic cycle use temperate phages

A

lysogenic

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17
Q

lysogenic cycle steps

A
  1. attachment/injection same as lytic
  2. integration of phage chromosome into host chromosome via recombination at specific DNA sequence found in both chromosomes
  3. excision of prophage in response to an environmental signal, through reversal of site-specific recombination leading to integration
  4. resumption of lytic cycle, beginning with phage-chromosome replication
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18
Q

bacterial transduction mediated by bacteriophages

A

transfer of genetic material from donor to recipient by way of a bacteriophage
- phage accidentally incorporates a fragment of donor DNA rather than copy of phage chromosome

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19
Q

how small are bacteriophage particles

A

less than 1% the size of the bacteria they attack

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20
Q

composition of bacteriophage

A
  • icosahedral head
  • hollow protein sheath
  • set of tail fibers
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21
Q

what does the head of a bacteriophage contain

A

single chromosome from 5,000 to 100,000 base pairs

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22
Q

what does replication and gene expression of bacteriophages require

A

enzymes and factors of the host cell

23
Q

what does the transfer of genetic material from a donor bacterium to a recipient via a phage lead to the production of

A

transductant bacterial strain

24
Q

2 types of transduction

A
  1. generalized transduction
  2. specialized transduction
25
Q

generalized transduction

A

transfer of random bacterial genes, carried out by bacteriophages that can’t distinguish between phage and bacterial DNA during packing of DNA into new phage particles

26
Q

specialized transduction

A

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

27
Q

generalized transduction steps

A
  1. normal P1attaches to donor bacterium and injects DNA into the cell
  2. replication of phage chromosome followed by transcription/translation to produce phage proteins
  3. some phages receive host DNA fragment instead of phage DNA
  4. host cell lysis releases all the progeny phages
  5. generalized transducing phages attach to new recipient cells and inject DNA
  6. homologous recombination may occur between donor fragment/recipient chromosome
  7. stable transductant strain results
28
Q

generalized transacting phage

A

phages that receive host DNAA fragment instead of phage DNA
- (random selection of DNA fragments based upon size alone)

29
Q

ex. of temperate phage

A

lambda phage

30
Q

where do lambda phages integrate into host chromosomes

A

at specific sites

31
Q

integration site in bacterial host chromosome

A

att site
- same 15-bp sequence

32
Q

integration site in lambda phage

A

attP

33
Q

integration site in E. coli host

A

attB

34
Q

how similar are the attB and attP sites

A

identical

35
Q

because attB/attP are identical, excision of prophage is usually…

A

exact reversal of the integration

36
Q

possible error in excision of specialized transduction

A

only part of prophage is removed, and along with it, some of nearby bacterial DNA

37
Q

what does aberrant excision produce

A

specialized transducing phage

38
Q

what genes are found on either side of attB site in E. coli

A

galK and bioA

39
Q

(lambda)dgal+ specialized transducing phage

A

includes galK gene
- can infect host cells but lacks genes needed to complete either lysis or lysogeny

40
Q

(lambda)dbio+ specialized transducing phage

A

includes bioA gene
- can induce lysis but lacks genes needed for lysogeny

41
Q

lateral gene transfer

A

transfer of genetic material between ind. bacteria or archaea and other organisms

42
Q

studies suggest that more than ____% of genes in a genome are the result of LGT

A

12

43
Q

what kind of genes are more likely to undergo LGT

A

genes encoding for cell surface proteins, DNA-binding proteins, and proteins related to pathogenicity

44
Q

where does LGT occur

A

among bacteria and between bacteria and eukaryotes

45
Q

evolutionary example of LGT

A

endosymbiosis that led to mitochondria and chloroplasts in eukaryotes

46
Q

another ex. of LGT

A

LGT of 10,000-30,000 base pairs from bacterium Agrobacterium tumefaciens to plants

47
Q

how is LGT identified

A

presence of DNA-sequence features in regions of a genome that are uniquely different from the rest of the genome

48
Q

genomic islands

A

regions of genome that are uniquely dif from rest of genome

49
Q

are genomic islands usually large or small

A

large (10-200 kb)
- often include multiple genes

50
Q

2 common characteristics of genomic islands

A
  1. group of genes much more like genes of distantly related species than closely related species
  2. ratio of G-C and A-T substantially different than rest of genome
51
Q

LGT medical importance

A
  • allowed for rapid organism adaptation to changing environmental conditions by acquiring antibiotic resistance
  • can lead to acquired pathogenicity islands
52
Q

pathogenicity islands

A

contain genes for proteins that promote host invasion and genes that produce toxic compounds

53
Q

ex. of pathogenicity islands in certain strains of E. coli

A

can cause diarrhea and meningitis

genetics (47 decks)

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