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PRIS > Bacterial Genetics > Flashcards

Bacterial Genetics Flashcards

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1
Q

Bacterial genetics are increasingly being used in veterinary - what are these uses?

A
  • Detection e.g., PCR
  • identification e.g., whole genome sequencing
  • epidemiology e.g., identify variants of concern, disease transmission pathways
  • determining antibiotic resistance and presence of virulence factors
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2
Q

What is the nucleoid?

A
  • a bacterial chromosome which is one large circular molecule (haploid)
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3
Q

How much longer is a nucleoid compared to a bacterial cell and what is its structure?

A
  • 1000 times longer than a bacterial cell and extensively folded to form a dense body that cam be visualised by electron microscopy
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4
Q

How many base pairs does a nucleoid have?

A
  • 0.8 - 0.4 x 10’6
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5
Q

One copy of what is given to the daughter cell?

A
  • nucleoid
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6
Q

What is a plasmid?

A
  • A plasmid is a large circular molecule of double-stranded DNA that replicate autonomously from the chromosome
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7
Q

What does a plasmid encode for?

A
  • Encodes genes for self-transmissibility
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8
Q

What do virulence factors help bacteria to do?

A
  • help bacteria to infect humans, animals and plants by a variety of mechanisms
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9
Q

What are way virulence factors can help bacteria?

A
  • some are toxins that damage or kill animal cells
  • others help bacteria attach to and invade animal cells
  • others protect bacteria against retaliation by the immune system
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10
Q

What are two examples of virulence plasmids?

A
  • Anthrax - bacillus anthracis contains pXO1 plasmid which encodes the bacterial toxin components and pXO2 plasmid which encodes the capsule which enables the bacteria to evade the immune system
  • E.coli O157:H7 - possesses the plasmid pO157 that encodes a periplasmic catalase that provides additional oxidative protection against the host defence mechanism . the shigella-like toxin is encoded by a prophage
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11
Q

What is a mutation?

A
  • an alteration of the nucleotide sequence from the wild-type
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12
Q

What is a phenotypic adaptation?

A
  • metabolic adjustment in the whole population to environmental conditions
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13
Q

What is genetic variation?

A
  • is the presence of differences in sequences of genes between individual organisms of a species
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14
Q

What does genetic variation enable?

A
  • enables natural selection, one of the primary forces driving the evolution of life
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15
Q

What does genetic variation within a group enable?

A
  • enables some organisms to survive better than others in the environment in which they live
  • organism of even a small population can differ in terms of how well suited they are from life in a certain environment
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16
Q

Genetic variation within a species can result from a few different sources - what are these?

A
  • mutations, the changes in the sequences of the genes un DNA
  • Gene transfer
  • the movement of genes between different groups of organisms
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17
Q

What is mycobacterium bovis and where does it reside?

A
  • the causative organism of bovine tuberculosis
  • resides within granulomas of the lung and draining lymph nodes with very little access to other organisms
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18
Q

Mycobacterium bovis has little to no opportunity for gene transfer so how is genetic variation generated?

A
  • generated by point mutation, gene duplication and indels (insertion or deletion of bases in the genome)
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19
Q

Where do E.coil and Salmonella reside?

A
  • reside in the intestine which are rich in bacteria (up to 5 x10’10 per gram)
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20
Q

How do E.coli and salmonella approach genetic variation?

A
  • in this environment gene transfer mechanisms are commonly used to generate genetic variation and to rapidly disseminate advantageous genetic info between organisms
21
Q

What is transduction?

A
  • injection of DNA into a bacterium by a phage
22
Q

What is conjugation?

A
  • plasmid in a donor bacterium is transferred though a pilus into a recipient bacterium
  • plasmid may integrate into the chromosome or remain in the cytoplasm
  • plasmid may be transferred between cytoplasmic and chromosomal locations
  • plasmid may exchange insertion sequences or transposons with other plasmids or the chromosome
23
Q

What is transformation?

A
  • uptake of naked DNA from the environment
24
Q

Gene transfer in bacteria can be what?

A
  • conjugated (plasmid-mediated)
  • transduction (phage mediated)
  • transformation (uptake of naked DNA)
25
Q

What is the Fertility factor (F factor)?

A
  • is a conjugative plasmid transferred from cell to cell by conjugation
  • is an episome = genetic element that can inset into chromosome or replicate as circular plasmid
26
Q

What is the F plasmid?

A
  • is a low-copy-number plasmid
    -100kb in length
  • present in 1-2 copies per cell
27
Q

How does the F plasmid replicate?

A
  • replicates once per cell cycle and segregate to both daughter cells in cell division
28
Q

In bacterial mating, conjugation and DNA transferer what is the direction?

A
  • unidirectional
29
Q

What is bacterial transformation?

A
  • the process of genetic alteration by pure DNA
30
Q

During bacterial transformation how do recipient cells acquire genes?

A
  • from DNA outside the cell
31
Q

How is DNA acquired in bacterial transformation?

A
  • may be natural
  • chemically
  • electrically induced
32
Q

In transformation what happens after DNA is taken up by the cell?

A
  • often recombines with genes in bacterial chromosome
33
Q

What can transformation alter?

A
  • may alter phenotype of recipient cells
34
Q

How are genes located close together transferred?

A
  • are often transferred as a unit to recipient cell = co transformation
35
Q

How are genes that are far apart transferred?

A
  • less likely to be transferred together
36
Q

What are transposable elements

A
  • DNA sequences that cannot self-replicate but can jump from one position to another or form one DNA molecule to another
37
Q

Bacteria contain a wide variety of what?

A
  • transposable elements
38
Q

The smallest and simplest insertion sequences or IS elements, which are 1-3kb in length contain what?

A
  • contain inverted repeat sequences of DNA and encode the transposase protein required from transposition and one or more additional proteins that regulate the rate of transposition
39
Q

How do transposable elements enhance genetic diversity and evolution?

A
  • by causing deletions and genetic rearrangement within replicons
40
Q

What is a transposon?

A
  • is where other transposable elements in bacteria contain one or more genes unrelated to transposition that can be mobilised along with transposable elements
41
Q

What can transposons do?

A
  • insert into plasmids which can be transferred to recipient cells by conjugation
42
Q

How are transposable elements flanked?

A
  • inverted repeats
  • often contain multiple antibiotic resistance genes
43
Q

Restriction and modification systems can be used as what?

A
  • defence mechanisms that bacteria use to prevent infection by foreign DNA (such as viruses)
44
Q

What two enzymes do modification and restriction systems consist of?

A
  • restriction endonuclease
  • methylase (or methyltransferase)
45
Q

What is restriction?

A

= cutting (site-specific endonuclease activity)
- is a means by which bacteria evade viruses or other incoming DNA

46
Q

What is modification?

A

= protection (site-specific endonuclease activity)
- modification is the protection of the organisms own DNA

47
Q

What does restriction endonucleases recognise?

A
  • specific sequences on the incoming DNA and cut them
48
Q

Methylases methylate has the same sequence in the bacterial genome to do what?

A
  • to prevent self-destruction (cutting) of its own DNA
49
Q

Adenosine or cytosine methylation are mediated by what?

A
  • restriction modification systems of many bacteria

PRIS (16 decks)

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