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Molecular biology of the gene > Horizontal gene transfer > Flashcards

Horizontal gene transfer Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

how does DNA transfer vertically in bacteria

A

it transfers from parent to progeny (offspring)

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2
Q

how does DNA transfer horizontally in bacteria

A

it transfers from one bacterium to another

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3
Q

what is transformation

A

the uptake of free floating DNA from the environment

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4
Q

what is transduction

A

DNA transfered via a bacteriophage

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5
Q

what is conjunction

A

DNA is transfer is plasmid mediated

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6
Q

what are the 3 possible fates of incoming DNA

A
  1. DNA may be degraded by restriction enzymes
  2. DNA will self replicate
    - only if it possesses its own origin of replication
  3. DNA may recombine with the host chromsome
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7
Q

what takes in the DNA after being released from the donor in transformation

A

DNA is released from a donor and taken in by a recipient known as a TRANSFORMANT

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8
Q

what is a recipient bacteria, prior to DNA uptake said to be

A

competence

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9
Q

what is natural competence

A

a natural state of bacteria in which they can take up DNA ~ 90 bacterial species identified

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10
Q

what is an artificially induced competence

A

chemical or electrical treatment to induce competence

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11
Q

what is the first stage of transformation

A

binding of dsDNA to the outer cell surface of the bacteria

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12
Q

what is the second stage of transformation

A

movement of the DNA across the membranes and cell wall

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13
Q

what is the third stage of transformation

A

degradation of one of the DNA strands

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14
Q

what is the fourth stage of transformation

A

translocation of the remaining ssDNA into the cytoplasm of the cell

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15
Q

what is the fifth stage of transformation

A

integration of the ssDNA into the recipient chromosome by homologous recombination

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16
Q

what are the genes involved in gram positive DNA uptake and competence called

A

com genes

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17
Q

which com genes are involved in the regulation of competence

A

comA and comK

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18
Q

which com genes are responsible for encoding structural proteins involved in DNA uptake

A

comE, comF and comG

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19
Q

is Bacillus subtilise gram positive or gram negative

A

gram positive

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20
Q

what does comEA do

A

comEA encodes the protein that directly binds dsDNA

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21
Q

what does the comG operon do n

A

the pore or channel proteins are encoded by the comG operon

22
Q

what does comF do

A

comF are the genes that translocated the DNA into the cell

23
Q

is Neisseria gonorrhoea gram positive or negative

A

gram negative

24
Q

what are the proteins involved with DNA uptake called of gram negative bacteria

A

they are named Pil

25
Q

what are are transformasomes

A

DNA uptake in H.influenzae is associated with the formation of numerous small membranous structures called transformasomes

26
Q

give an example of species specification

A

Neisseria spp. and haemophilus spp. only take up DNA from their own species

27
Q

what are the 3 responses/ adaptation mechanisms when cells are faced with a shortage of nutrients

A
  1. induction of flagellar synthesis
  2. induction of competence (transformation)
  3. sporulation (gram positives)
28
Q

describe induction of flagella synthesis

A

it is the least drastic response, permits cells to swim to new sources of nutrients

29
Q

describe induction of competence

A

more radical survival measures, cell exposes itself to a mutagenic process (HGT)

30
Q

describe sporulation

A

dormant state to survive adverse conditions

31
Q

name 3 evolutionary advantages of horizontal gene transfer

A

nutrition
repair
diversity generation

32
Q

how is nutrition an evolutionary advantage

A

uptake of exogenous DNA are C & N rich source
complete breakdown of DNA in the extracellular environment would make it available to other cells, makes sense to import first

33
Q

how is repair an evolutionary advantage

A

uptake of homologous DNA would allow repair of mutated sequences
could explain why some bacteria only uptake DNA from the same species
there is no evidence to support competence is induced by DNA damage

34
Q

how is diversity generation an evolutionary advantage

A

uptake and integration of ‘foreign’ DNA allows the assembly of new combinations of genes
increases diversity and speeds up evolution, especially, when the ‘foreign’ DNA is derived from different strains/ species/ genera

35
Q

how is horizontal gene transfer artificially induced

A

calcium ion induction
electroporation

36
Q

what does calcium ion induction enable

A

it enables uptake of ss and dsDNA (including plasmids)

37
Q

what is electroporation

A

bacteria are mixed with exogenous DNA and briefly exposed to a strong electric field
it opens cells cup and moves DNA into the cells
it can be used to transforms most bacteria

38
Q

what is transduction

A

DNA transferred via a bacteriophage

39
Q

what is a bacteriophages

A

viruses that infect bacteria

40
Q

describe the structure of phages

A

they have a capsid or icosahedral head and an elaborate tail structure

41
Q

what do bacteriophages inject bacterial cells with

A

bacteriophages inject their DNA into a bacterial cell

42
Q

are phages living organisms

A

phages are not living organisms

43
Q

describe a phage

A

they are nucleic acid (DNA/RNA) wrapped in a protein and/or membrane coat (protection)

44
Q

what happens in the lytic cycle

A

the virus introduces its genome into a host cell and initiates replication by hijacking the host’s cellular machinery to make new copies of the virus.

45
Q

what are the 5 stages of the lytic cycle

A
  1. a phage absorbs to an actively growing bacterial cell, by binding to specific cell surface receptors
  2. phage injects its entire DNA into the host cell and transcription of the viral genes commences
  3. the phage DNA begins to replicate and copies accumulate
  4. numerous phage particles are completed, and phage DNA is taken up by the heads
  5. the host cell lyses and newly made phages are released
46
Q

what is generalised transduction

A

any region of the bacterial DNA can be transferred from one bacterium to another via the bacteriophage

47
Q

what is specialised transduction

A

only certain genes, usually those close to the attachment site of a lysogenic phage can be transferred

48
Q

what makes a transfusing phage

A

the phage must not degrade the host DNA completely after injection, or no host DNA will be available to transfer

the packaging, or pac sites of the phage must not be so specific that such sequences will not occur in the host DNA

49
Q

describe P1 phage

A
  • good transducer of gram - bacteria
  • low pac site specificity
  • very broad host range for adsorption and transduction
50
Q

describe P22 phage

A
  • the salmonella enteric server Typhimurium phage
  • good transducer
  • low pac site specificity
  • some regions of salmonella DNA will be transduce at a higher frequency
51
Q

what are the 2 properities that distinguish specialised transduction from general transduction

A
  • only bacterial genes close to the attachment site of the prophase can be transduced
  • the specialised transfusing phage carries both bacterial and phage genes
52
Q

how do you distinguish a lysogenic phage

A

lysogenic phages are able to maintain a stable relationship with the host cell, in which they neither multiply nor are they lost from the cell

Molecular biology of the gene (1 decks)

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