viruses and bacteria genetics Flashcards

1
Q

what makes bacteria valuable research objects

A
  • small size
  • rapids reproduction
  • selective media that can easily identify the presence of an active allele
  • simple physiology (monoploid)
  • genetic variability
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2
Q

bacteriophages

A
  • bacterial viruses
    -reproduce by infecting bacterial cells
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3
Q

colony

A

population that derives from a single bacterium, all have the same genotype

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4
Q

dilution series

A

help pick out a single colony, easier to do when they are more spread out
- will isolate same species of bacteria that has genetic variation

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5
Q

plaques

A

bacteriophages produce clearances on plates with dense bacterial cultures within hours of infection

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6
Q

Bacteriophage T4

A

docs to surface of bacteria and injects its genetic material into the bacterium
- virus itself does not enter the cell
- protein coat (especially in virus head) envelopes genetic material
- goes through a lytic phase - lyses the cell to infect other cells

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7
Q

Bacteriophage lambda

A
  • may be lytic or lysogenic
  • genome contains 48,502 base pairs and about 50 genes
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8
Q

retrovirus

A
  • has RNA genome
  • less stable than DNA and more prone to degradation since it is single-stranded
  • more adaptable because higher rate of mutations
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9
Q

retrovirus cycle

A
  • virus attaches to host cell at receptors in the membrane and viral core enters host cell
  • RNA degrades and reverse transcriptase synthesizes second DNA strand
  • viral DNA enters the nucleus and is integrated in host cell chromosome forming a provirus
  • proviral DNA is transcribed to viral RNA which is exported to cytoplasm where it is translated and new material is assembled
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10
Q

lytic cycle

A
  • phage binds to the bacterium and its DNA enters host cell
  • host DNA is digested
  • phage DNA replicates
  • host cell transcribes and translates phage DNA into proteins
  • assembly of new phages is complete and are released to start the cycle again
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11
Q

sensor proteins

A

stimulus that tells prophage from the lysogenic cycle to enter the lytic cycle
- can detect if bacteria is healthy and wants to infect them

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12
Q

lysogenic cycle

A
  • phage binds to the bacterium and its DNA enters the host cell
  • phage DNA integrates into the bacterial chromosome (through crossing over) and becomes a prophage
  • prophage is replicated as part of the bacterial chromosome
  • the prophage may separate from the chromosome and the cell will enter the lytic cycle
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13
Q

prophage

A

inactive phage that is dormant in the host genome

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14
Q

Genomes of bacteria

A
  • genomes are circular, called bacterial chromosomes
  • additional genetic material resides in plasmids and can replicate independently
  • episomes are large circular DNA that can integrate into the bacterial chromosome for replication or stay separate
  • bacteria do not have meiosis, therefore no chiasmata or homologous pairs
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15
Q

Gene transfer in bacteria

A

unidirectional - from donor cell to recipient
- never an exchange

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16
Q

how can gene mutations be observed in bacteria

A
  • colony colour and morphology
  • nutritional mutants (cannot metabolize certain sugars)
  • prototrophs (can make AAs needed) and auxotrophs (can’t make AAs needed)
  • antibiotic resistance
17
Q

how can you isolate a bacterial strain that cannot synthesize leucine

A
  • plate bacteria on a medium containing leucine, both leu+ and leu- grow
  • replica plate the colonies by pressing a velvet surface to the plate, cells adhere to velvet
  • Press onto new petri plates,
  • leu- are recovered from colony
18
Q

what does a missing colony state

A

a colony that grows only on the supplemented medium has a mutation in a gene that encodes the synthesis of an essential nutrient

19
Q

how do bacteria exchange genetic material

A

through parasexual processes
- conjugation
- transformation
- transduction

20
Q

transformation

A

transfer of a free (out of the cell) piece of DNA from one bacterium into another
- sensitive to DNase
- does not require cell contact

21
Q

conjugation

A

direct transfer of DNA from one cell to another via the establishment of a cytoplasmic bridge
- not sensitive to DNase (since DNA never touches outside environment)
- requires cell contact

22
Q

transduction

A

transfer of genes from one cell to another via bacteriophage
- not sensitive to DNase (since virus head is protecting DNA)
- does not require cell contact

23
Q

U-tube experiment

A
  • asks how did the genetic exchange of leucine take place
  • 2 different strains of bacteria separated by a barrier that allowed mixing of medium but not bacteria
  • since no prototrophic bacteria were produced we conclude genetic exchange requires direct contact between bacteria cells
24
Q

plasmid

A

an extra-chromosomal circular piece of DNA that can replicate independently of the chromosome
- not required for the survival of host cell and serve as auxiliary genetic elements

25
Q

R plsdmid

A

resistant plasmids

26
Q

F factor

A

fertility factor - an episome

27
Q

epsiome

A

a genetic element that is not essential to the most and that can either replicate autonomously or be integrated into the bacterial chromosome