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Microbiology > Bacterial Genetics > Flashcards

Bacterial Genetics Flashcards

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Biology 101 flashcards
1
Q

What are two ways that bacteria experience genetic change?

A
  1. Mutations

2. Horizontal Gene Transfer

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2
Q

What is horizontal gene transfer and what is one result from it

A
  • transferring mutated genes to other bacterial cells belonging to the same generation
  • reason for antibiotic resistance
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3
Q

T/F Bacteria are diploid cells

A

False, haploid, so they only have one copy of a gene, no backup.

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4
Q

What are the three mechanisms in which genes are naturally transferred in horizontal gene transfer

A
  1. Transformation
  2. Transduction
  3. Conjugation
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5
Q

What happens to a bacterial cell when it receives DNA from Horizontal gene transfer

A
  • DNA replicated only if replicon
  • Replicon has origin of replication
  • Has Plasmids, Chromosomes
  • DNA fragments added to chromosome via homologous recombination
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6
Q

In what situations will all of the daughter cells have a copy of the DNA fragment, in what situation will only one

A
  • If the DNA fragment is integrated into a bacterial chromosome
  • If there is no origin of replication, the DNA molecules will not be able to replicate
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7
Q

DNA-mediated transformation

A

Dead donor cell will release naked DNA uptake by bacteria, gets incorporated into the host chromosome by homologous recombination

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8
Q

Griffiths Experiment

A

-only encapsulated cells are pathogenic

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9
Q

S- strain in Griffiths Experiment

A

-Smooth strain because they have a capsule around them, can invade immune system and kill mouse

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10
Q

R-strain in Griffiths Experiment

A
  • Rough strain that has lost its capsule

- immune system will capture R strain and destroy it before it infects mouse

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11
Q

What happens with a heat killed S-strain

A

still has capsule but are not alive so there is no effect on the mouse

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12
Q

What happens when a heat-killed encapsulated cell (dead s-strain) and a living r-strain are injected in Griffiths Experiment

A

The Mouse dies because transformation has occurred because R-strain becomes S-strain and infects

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13
Q

What horizontal gene transfer does Griffiths Experiment represent

A

DNA-mediated Transformation

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14
Q

What is important for the recipient cell in transformation

A

It needs to be competent, which means that their cell wall and cell membrane has been altered to allow macromolecules to enter

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15
Q

Specificity of recipient cell in transformation

A
  • Most take up regardless of origin

- Some accept only from closely related bacteria (DNA sequence)

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16
Q

Nature of DNA being transferred in transformation

A

fragmented DNA (ss-DNA) floating around the cell, only a single strand is allowed to enter and the other strand gets degraded

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17
Q

How much DNA is transferred in transformation

A

about 20 genes

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18
Q

What is the effect on the donor and recipient cell in transformation

A

Yes sensitivity to DNase, destroys the DNA being transferred and prevents transformation

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19
Q

What are the two types of Transduction?

A

Generalized Transduction and Specialized Transduction

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20
Q

What are the donor cells in transduction

A

transfer of genes by bacteriophages

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21
Q

Generalized Transduction

A
  • any genes of donor cell

- any piece of donor DNA can be donated

22
Q

What kind of bacteriophage carries out generalizes transduction

A

A lytic bacteriophage

23
Q

Specialized transduction

A

specific genes, requires an infection caused by a temperate bacteriophage (needs to undergo lysogeny) specific preferences to the part of donor DNA that is being transferred

24
Q

How much DNA is being transferred in Transduction

A

Small fraction of the chromosome

25
Q

What are the 3 ways a transducing phage can be produced

A
  1. packaging error during phage assembly
  2. Degradation of host chromosome; fragments mistakenly packaged into phage heads
  3. These phages cannot direct phage replication cycle
26
Q

Steps in generalized transduction (5)

A
  1. bacteriophage attaches to a specific receptor on a host cell
  2. Phage DNA enters the cell, empty phage coat remains on the outside of bacterium
  3. enzymes encoded by the phage genome cut the bacterial DNA into small pieces
  4. Phage nucleic acid is replicated and coat proteins synthesized
  5. During construction of viral particles, bacterial DNA can mistakenly enter a protein coat, this creates a transducing particle that carries bacterial DNA instead of phage DNA
27
Q

What occurs with the new phage particles produced in generalized transduction? and what are they called

A
  • called generalized transducing particles
  • can’t direct phage replication
  • bind to new host and can inject DNA which may integrate via homologous recombination
  • resulting in any gene from donor cell to be transferred
28
Q

How many phages are typically packaged with bacterial DNA in generalized transduction

A

only about one or two out of 200

29
Q

T/F there is a preference for particular DNA pieces in general transduction

A

False, it will happen randomly and there is no preference

30
Q

Which is the only process that is affected by DNase

A

transformation

31
Q

What are the three mechanisms that will cause specialized transduction

A
  1. Excision mistake during transition from lysogenic to lytic cycle of temperate phage
  2. Short piece of flanking DNA removed along with phage DNA
  3. Excised DNA incorporated into phage heads; defective particles released
32
Q

What are the major differences between generalized and specialized transduction

A

The phage used, type of DNA being transferred and also how many phage particles are able to participate

33
Q

describe details of the specialized transduction error in excision process

A
  • When the prophage is excised from a bacterial chromosome, a mistake is made and some bacterial DNA flanking the phage
  • DNA is taken and a piece of the phage DNA is left behind
34
Q

Why is the phage considered defective after specialized transduction

A

because it doesn’t carry the entire phage genome anymore

35
Q

How many of the bacteriophages contain the bacterial DNA after specialized transduction?

A

All of them, because the replication and assembly produces defective phage particles that carry certain bacterial DNA in place of some phage DNA

36
Q

Can DNA of a defective phage cause an infection once injected into a new host after specialized transduction

A

NO, since it does not carry the entire phage genome

37
Q

What happens to the recipient cell when a bacteriophage binds after specialized transduction

A
  • the DNA will be injected and the bacterial genes may integrate via homologous recombination
  • only bacterial genes adjacent to integrated phage DNA are transferred
  • phage DNA particles will be fragmented and not incorporated in the new host DNA
38
Q

Conjugation

A

Requires plasmid and direct transfer of DNA between donor and recipient

39
Q

Are all plasmids transferred in conjugation?

A

No only conjugative plasmids, which direct their own transfer

40
Q

What examples of plasmids are transferred with conjugation

A

F plasmids
R-plasmid= “resistant plasmids”
Ti: Tumor inducing plasmids

41
Q

What are the two types of conjugation

A

Plasmid transfer conjugation and plasmid + chromosomal conjugation

42
Q

What type of DNA is transferred in plasma transfer conjugation

A

an entire single strand of plasmid DNA

43
Q

What is the difference between F+ cells and F- cells in conjugation

A

F+ cells contain an F-plasmid (donor cell), F- do not (recipient cell)

44
Q

What is the use of the F pilus in conjugation

A

a hollow structure through which the plasmids can be transferred, which is why it is not susceptible to DNase

45
Q

Describe the process of plasmid transfer

A
  1. Pili bring cells into contact
  2. Enzyme cuts plasmid at the origin of transfer
  3. Pilus retracts and pulls the donor and recipient cells together
  4. Single strand transferred (now donor and recipient each have a single strand)
  5. Complementary strands are synthesized, now are dsDNA
  6. Both cells become F+
46
Q

Which is more common, plasmid only conjugation or plasmid + chromosome transfer conjugation

A

plasmid transfer conjugation

47
Q

In plasmid + chromosome transfer conjugation, what are Hfr cells

A
  • cells where the plasmid is incorporated in with the host chromosome
  • cells that have high frequency of recombination
48
Q

How is a F+ cell different from an Hfr cell

A

the F+ cell has its own chromosome and plasmid exists as extra chromosomal DNA

49
Q

T/F the process of switching between a F+ and Hfr cell is reversible

A

True

50
Q

What is the mechanism behind chromosomal DNA transfer in conjugation

A
  1. Hfr cell produces F pilus
  2. Transfer begins with genes on one side of the origin of transfer or plasmid
  3. Part of chromosome is transferred to recipient cell when the donor is Hfr
  4. Chromosome usually breaks before complete transfer
  5. Recipient cell remains F- since incomplete F plasmid transferred
51
Q

explain the mechanism behind why the recipient cell remains F- in plasmid and chromosome transfer

A

The DNA will get cut in the center of plasmid DNA region in order to get transferred and will be followed by the chromosomal DNA, only a part of a plasmid and part of a chromosome will get transferred. Does not include an entire plasmid, which is why it stays in the F- state. Does not become Hfr because it does not have the entire plasmid incorporated into the DNA, called a F-recombinant cell

Microbiology (7 decks)

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