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Genetics > Prokaryotic Gene Structure 3 > Flashcards

Prokaryotic Gene Structure 3 Flashcards

horizontal gene transfer

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Biology 101 flashcards
1
Q

how do bacteria replicate?

A

through process of asexual reproduction process called binary fission

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2
Q

what is DNase I ? (2)

+ what it acts on

A
  • an endonuclease that nonspecifically cleaves DNA,
  • acts on single & double stranded DNA, chromatin & RNA:DNA hybrids
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3
Q

what are the 3 types of horizontal gene transfer (lateral gene transfer)?

A

1. conjugation
2. transduction
3. transformation

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4
Q

how does HGT occur?

A

through mobile genetic elements (MGEs) (plasmids, transposons, viruses) that enter bacterial cell

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5
Q

what makes up the total genome?

A

bacterial genome + MGEs

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6
Q

what is the supergenome?

A

total number of genes available to bacterial community (large number of cells) via MGEs within same environment

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7
Q

what is metagenome?

A

the collection of supergenomes within the wider environment

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8
Q

what is conjugation?

A

donor bacterial cells transfers plasmid DNA to a recipient bacterial cell only when both cells are in physical contact through a specialised pilus (sex pilus)

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9
Q

what is transformation?

A

recipient bacterial cell takes up cell-free/naked DNA from the environment

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10
Q

what is transduction?

A

transfer of DNA from donor bacterial cell to recipient that is mediated by a bacteriophage

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10
Q

what are de novo mutations? (3)

A
  • single nucleotide polymorphisms (SNPs)
  • insertions
  • deletions (indels result in frameshift)
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11
Q

how do plasmids vary in size?

A

< 2000 bp to > 100 000 bp

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12
Q

what are the 2 forms of plasmids?

A

circular dsDNA (common)
linear dsDNA (rare)

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13
Q

what are the 6 types of plasmids? (12)

A
  1. fertility (F) plasmids (direct conjugation)
  2. resistance (R) plasmids (resistance to antibacterial agents)
  3. col plasmids **(for colicins, bacteriocins in pneumococcal defense)
  4. metabolic (degradative) plasmids (for metabolism of unusual molecules)
  5. virulence plasmids (pathogenicity to host bacterium)
  6. cryptic (no obvious phenotype)
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14
Q

what was the conclusion of lederberg & tatum’s experiment?

A

auxotrophic bacteria can be converted to prototrophs through gene transfer & recombination

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15
Q

what was the conclusion of davis’ experiment?

A

physical contact between 2 bacterial cells is required for conjugation

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16
Q

what did william hayes discover about genetic transfer? (2)

A

was polar (occurred in one direction), thus not reciprocal (one is a definite donor and definite recipient)

17
Q

what is F+?

A

donors that donate fertility factor (F)

18
Q

what is F- ?

A

recipient cells of the fertility factor

19
Q

what is mating pair formation?

A

conjugation bridge/pore forms between F+ and F- cells, membranes fuse to allow DNA to pass through

20
Q

what are the steps of conjugation (F+ x F- mating) (4)

A
  1. F+ produces sex pilus to contact F- → contact made → pilus contracts to bring F- cell closer
  2. mating pair formation
  3. one DNA strand on F plasmid is nicked at oriT & separates → intact F plasmid replicated in F+ cell. 5’ end of nicked DNA passes into F- via pore. as ssDNA of F plasmid enters F- = replicated to become dsDNA producing F plasmid copy (F- becomes F+)
  4. F+ plasmids produce surface exclusion proteins (prevent host cells from conjugating w other F+ cells)
21
Q

what are the two surface exclusion proteins ?

and what do they do

A
  • TraT blocks mating pair formation
  • TraS blocks DNA transfer at pore

traS: Stops (after connection)
traT: Terminate (before connect)

22
Q

what are Hfr strains?

A

bacteria with integrated plasmid that can transfer their chromosome & transfers chromosomal genes with high efficiency

23
Q

what are the two methods through which plasmids can integrate into chromosomes?

A
  1. recombination between shared sequences on plasmid & chromosome
  2. recombination via insertion elements shared between chromosome & plasmid
24
Q

what are the 3 steps of episomal insertion?

A
  1. association of plasmid & bacterial insertion sequences
  2. integration of F plasmid in bacterial chromo
  3. F plasmid intact (with O origin of transfer sequence → directs transfer of genetic material between bacterial cells)

integration is reversible (F plasmid can be excised & exist independently again)

25
Q

what happens when Hfr cells mate with F+ cells?

A

Hfr cells revert to F+ cells if F plasmid is excised from chromosome

26
Q

how is it formed

what is the F’ plasmid

A

when the F episome excises itself from chromosome and an error occurs, where it picks up a portion of the chromosome, making it distinct from the F plasmid

27
Q

what is a potential result from the mating of F’ x F-?

A

can transfer bacterial genes acquired during excision, recipients becomes F’ and is a partial diploid (merozygote)

28
Q

explain the general concepts of transformation

A
  1. bacterial uptake mechanisms allow them to take up DNA
  2. DNA fragment in medium binds to cell-surface receptor
  3. extracellular endonuclease cuts dsDNA into smaller fragments
  4. one DNA strand degraded = remaining strand transported into cell
  5. single strand aligns itself with homologous region on bacterial chromosome (recombination)
29
Q

what was the conclusion of hershey & chase’s study

A

only DNA of virus needs to enter a bacterium to infect it

30
Q

what was the conclusion of avery, mcleod & mccarthy experiment

A

DNA carries info responsible for transformation

31
Q

what are the two types of transformation?

A

natural & artificial

32
Q

what are competent cells?

A

cells that can take up DNA

33
Q

how can bacteria be artificially induced tp become competent

A
  1. chemical treatment (Ca ions makes bacteria competent - increase permeability of membrane)
  2. electroporation (wash w cold, non ionic solution to prevent arcing = high potential diff is applied across washed bacterial cells mixed with naked DNA = strong electric field creates hydrophilic pores
34
Q

what was the conclusion of ledeberg & zinder’s experiment?

A

genetic exchange didn’t take place by conjugation (bacteriophage was agent of transfer)

35
Q

why can bacterial genes incorporate into a phage capsid

A

because of errors made during virus life cycle

36
Q

what are the 2 types of transduction?

A
  1. generalised transduction
  2. specialised transduction
37
Q

describe the steps of the bacteriophage lytic cycle (4)

A
  1. adsoprtion & penetration (phage attaches to specific receptor on cell & injects phage dsDNA)
  2. phage forces bacteria to make virus DNA & proteins
  3. daughter phages assembled (virus DNA is packaged into virus protein coat)
  4. mature viruses released by cell lysis
38
Q

what are virulent phages ?

A

phages that reproduce using a lytic cycle

39
Q

explain generalised transduction

A

1.phage DNA enters host, bacterial chromosome is degraded
2. packaging of viral chromosomes into capsid = some fragments of degraded bacterial DNA can be packaged → generalised transducing particle
3. bacterial DNA is injected by transducing particle into another bacterial cell (no initiation of lytic cycle because no phage DNA)
4. 3 possible outcomes for injected bacterial dsDNA

occurs during lytic cycle

40
Q

what are the 3 possible outcomes for injected bacterial dsDNA?

A
  • integration into host genome (stable)
  • non-integration but genes expressed (abortive transduction – bacterial cell is a partial diploid)
  • degradation of DNA
41
Q

explain specialised transduction (3)

A
  • carried out only by temperate phages that have established lysogeny
  • only specific portion of genome transferred
  • when prophage is incorrectly excised

Genetics (14 decks)

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