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Bacteriology > Lecture 4/5 - Microbial Genetics > Flashcards

Lecture 4/5 - Microbial Genetics Flashcards

1
Q

What is an immunogen?

A

Any antigen that can elicit an immune response

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2
Q

What is an epitope?

A

Part of the antigen that binds to the antigen receptors

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3
Q

Where do mutation occur in surface Ag’s of a pathogen?

A

Within the nucleic acids – DNA/RNA

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4
Q

What is the results of the a mutation within the surface antigens of a pathogen?

A

Change in the structural proteins
– or –
Enzymes responsible for it’s assembly

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5
Q

What is the direct impact of genetic mutations in a pathogen?

A

Host immune response

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6
Q

Where is the H antigen found?

A

Flagella

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7
Q

Where is the O antigen found?

A

LPS

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8
Q

What are three methods to which antigenic mutations occur?

A

Drift + Shift + Switching

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9
Q

What are the two subtypes of antigenic switching?

A

Phase variation
– and –
Gene conversion

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10
Q

What can undergo antigenic shift?

A

Bacteria + Viruses

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11
Q

What can undergo antigenic shift?

A

Viruses

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12
Q

What can undergo antigenic switching?

A

Bacteria + Protozoa + Fungi

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13
Q

What is the process of antigenic drift?

A

Overtime population accumulates point mutations.

Leads to proteins products being altered causing distinct new strains of the bacteria

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14
Q

Where does antigenic drift tend to occur on a flu virus?

A

H antigen

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15
Q

What are the two components of the flu virus envelope spikes?

A

Hemaglutttinin
– and –
Neuraminidase

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16
Q

What is hemagluttinin?

A

Glycoprotein spike which attaches to the host receptors

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17
Q

What is neuraminidase?

A

Enzyme on the glycoprotein spike that releases from virus from the host cell

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18
Q

What is the structure of the flu viruses genome?

A

8 segments of ssRNA

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19
Q

What is the example of antigenic shift seen in the flu virus, that is given in lecture?

A

Two different strains (ie. human + birds), populate the same cell and undergo reassortment. this creates a whole new subtype of flu virus.

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20
Q

What is so dangerous about antigenic shift in the flu virus?

A

Can easily cause a pandemic because no species has been exposed to it. therefore no one has built immunity, leading to quicker spread of the virus.

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21
Q

Which genomic mutation is responsible for why we need yearly flu vaccines?

A

Antigenic drift

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22
Q

What genomic mutation is responsible for why there are flu pandemics in the world?

A

Antigenic shift

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23
Q

What are two important things that a successful pathogen must do?

A

Multiply in host
– and –
Evade the immune system

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24
Q

What is the mechanism of phase variation, a type of antigenic switching?

A

The gene is always apart of the cell genes but not always apart of the phenotype, but it is turned on and off depending on the current environment

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25
Q

What does phase variation lead to?

A

Phenotypic variation and therefore surface antigen variation. Go from having no flagella to having one

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26
Q

How is phase variation regulated?

A

Inversion of DNA sequence via recombinase

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27
Q

What are the two important components of a bacterial gene?

A

Promoter + Coding sequence

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28
Q

What is another name for gene conversion, a method of antigenic switching?

A

Gene shuffling

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29
Q

What is the mechanism of gene conversion?

A

Recombination within a specific group of genes. The phenotype is always there but the bacteria can switch through types, like changing a shirt. Biological function remains the same

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30
Q

What pathogen causes relapsing fever?

A

Borrelia recurrenntis

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31
Q

Why does relapsing fever occur?

A

Gene conversion; switches through serotypes causing the immune system to stop being able to recognize it.

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32
Q

What is responsible for malaria?

A

Plasmodium falciparum

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33
Q

What method is used by malaria to evade the immune system?

A

Variable surface glycoproteins aka VSG; does this by avoiding splenic destruction by attaching to endothelium

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34
Q

What are mobile genetic elements?

A

Segments of DNA that encode for enzymes/proteins that mediate movement of DNA within the genome or between cells

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35
Q

What are the two groups of MGE?

A

Replicons
– and –
No replicons

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36
Q

What is the basic method of the replicon?

A

Replicate DNA/RNA independently of host cell chromosome

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37
Q

What is the basic method of cells that are not replicons?

A

Replicate DNA/RNA as part of cell chromosome or plasmid DNA

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38
Q

What is different about a bacteriophage compared to a plasmid genetically?

A

RNA + DNA (plasmids are DNA only)

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39
Q

What do plasmids tend to carry?

A

Non-essential genetic information

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40
Q

What do plasmids allow for in a bacteria?

A

Selective advantage, especially when an AB is present

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41
Q

What are R plasmids?

A

Resistance plasmids, carry 1+ genes for AB resistance

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42
Q

What is special about R plasmids?

A

They are not genera specific and can be shared amongst any bacteria for the most part

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43
Q

What are bacteriophages?

A

Bacteria viruses

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44
Q

What do bacteriophages do?

A

Inject DNA into bacteria and use the host machinery to copy it’s DNA. Then use the lytic or lysogenic cycle to break out of the bacteria

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45
Q

Can bacteriophages move amongst genera?

A

No, they are genera specific.

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46
Q

What are the three mechanisms that bacteria user to exchange DNA among bacteria?

A

Transformation - Conjugation - Transduction

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47
Q

In general, what is transformation in regards to genetic exchange?

A

Incorporation of exogenous (aka naked DNA) into cytoplasm (via plasmid) or chromosome

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48
Q

In general, what is conjugation?

A

Mating leading to exchange of genetic information from one bacterium to another

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49
Q

In general, what is transduction?

A

Transfer of bacterial DNA from one bacterium to another via bacteriophage

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50
Q

How is naked DNA, from transformation, incoporated into the genome of the receiving bacteria?

A

Homologous recombination + Nonhomologous recombination

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51
Q

When does invitro competence normally develop in bacteria?

A

During the log phase of cell culture

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52
Q

What does naturally competent mean?

A

Process of natural transformation, meaning the cells have the ability to undergo this process. Which is not common

53
Q

When does recombination of DNA occur in a bacteria?

A

When cell takes up new DNA and it does not have a bacterial origin

54
Q

What happens if the DNA is rejected in transformation?

A

Restriction enzymes cut it up

55
Q

What does homologous recombination require?

A

Sequence similarity between donor and recipient

56
Q

What does homologous recombination use to be successful?

A

Recombination gene products (aka Rec proteins)

57
Q

What are the two mechanisms by which nonhomologous recombination can occur?

A

Random or Site Directed

58
Q

What occurs with random nonhomologous recombination?

A

Gene is randomly inserted, recombined with host DNA. Can lead to distruption of the genetic makeup of that bacteria. Especially if it is placed within a promoter or coding sequence of a gene

59
Q

What is it call when there is a failed attempt at non-homologous recombination with random insertion?

A

Null mutaiton

60
Q

How is the site-directed nonhomologous recombination done?

A

Has a specific sequence - “CATGCAC”

No REC proteins are needed

61
Q

What is the end result of nonhomologous recombination?

A

Addition NOT replacement of chromosomal DNA

62
Q

What is the most common method of genetic exchange?

A

Conjugation

63
Q

What is the pro of conjugation?

A

Can occur between bacteria of the same species or different ones; depends on the plasma type involved

64
Q

What occurs with conjugation?

A

One way transfer between donor and recipient bacteria

65
Q

What directs Conjugation?

A

Genes on the plasmid DNA

66
Q

What type of plasmid carry information for plasmid mobilization?

A

Conjugative plasmids

67
Q

What can also be carried on conjugative plasmids?

A

Bacteriocins + AB resistance

68
Q

What genes are important for the conjugative process?

A

Transfer of plasmid (making the recipient a donor)
Ability to make sex pilus
Initiate plasmid DNA synthesis

69
Q

What system is needed to carry out the DNA transfer in conjugation?

A

T4SS - Type IV secretory system

70
Q

What bacteria has T4SS been ID’ed in?

A

Gram-negative, but similar system found in Gram-positive.

71
Q

What designates whether a bacteria is the donor or the recipient?

A 
F+ = donor = male
F- = recipient = female
72
Q

What is a conjugant cell?

A

When F+ and F- are attached

73
Q

What determines what mating type a cell is?

A

Presence of F plasmid

74
Q

What is the result of plasmid transfer?

A

Plasmid moved as linear ssDNA
– and –
Rolling circle replication

75
Q

What is rolling circle replication?

A

Produces dsDNA plasmid in recipient AND DONOR cell

76
Q

Where does mobilization being in rolling circle replication of a plasmid?

A

Plasmid-encoded protein causing single-stranded, site-specific cleavage at oriT

77
Q

What initiates rolling circle replication?

78
Q

What is responsible for directing the linear strand of plasmid?

A

T4SS - In Gram-negative bacteria

79
Q

What is the steps in rolling circle replication?

A

Transfer of ssDNA + Recircularize/Replication = dsDNA

80
Q

What is an antigen?

A

Any molecule that can be bound by antibody, T cell receptor, or MHC

81
Q

How does gram-positive conjugation occur?

A

Adhesion molecules on surface of the donor cells

NO SEX pilus

82
Q

What occurs with high frequency recombination?

A

Before conjugation begins - F plasmid intergrats into IS/Tn within host chromosome

83
Q

How does the F plasmid during Hfr intergrate itself within the host chormosome?

A

Via nonhomologous recombination

84
Q

What is the definition of a Hfr cell?

A

Host cell with integrated F plasmid

85
Q

What is an episome?

A

A replicon that can exist either seperate from the host cell chromosome or as part of the chromosome

86
Q

What does Tn stand for?

A

Transposon

87
Q

What is IS stand for?

A

Insertion sequence

88
Q

What is an integrated plasmid?

A

Plasmid that has been integrated into the host cell chromosome

89
Q

What is the order of chromosome transfer when a Hfr cell is involved?

A

First 1/2 of the F plasmid + Chromosome + Second 1/2 of F plasmid

90
Q

Why is there a chance that conjugation with a Hfr cell might be incomplete?

A

Cellular connection is fragile and the DNA is long, may break before finished.

91
Q

What is the highest probable ending to conjugation involving a Hfr cell?

A

Transfer of the first 1/2 of the F plasmid and a portion of the adhacent chromosome. Meaning the F- cell does not become an Hfr cell

92
Q

What occurs with full transfer of the Hfr genome?

A

Conversion of the F- cell to the Hfr cell

93
Q

What mediates the process of transduction?

A

Bacterial viruses aka bacteriophages

94
Q

What is the basic process of genetic transfer in regards to transduction?

A

Phage picks up fragments of bDNA and packages them into virions (phage particles). bDNA is then delivered to infected cell

95
Q

What happens to the bDNA once a bacteriophage introduces it to the infected cell?

A

Incorporated into bacterial genome via homologous recombination

96
Q

What are the three structural components of a bacteriophage?

A

Capsid + Tail + Nucleic acid core

97
Q

What are the two mechanisms for escape from the host cell that virulent phages use?

A

Lytic or/and Lysogenic

98
Q

What are the basic steps that occur in the lytic cycle?

A 
Attaches/Absorption 
Injection/Penetration 
Replication 
Assembly 
Lysis (once enough are made)
99
Q

What is the key to generalized transduction?

A

The Lytic Cycle

100
Q

What is still present during the phage assembly of the lytic cycle?

101
Q

What happens when a viral capsid is packed with bDNA?

A

becomes a Defective phage and can only attach to a new host cell and inject bDNA, where recombination with host chromosome is carried out

102
Q

Why does a viral capsid sometimes get bDNA?

A

Doesn’t know the difference between bDNA or vDNA

103
Q

What is important about the lytic cycle, in regards to what it involves?

A

Virulent phages, but if accidentally pick up bacteria this changes

104
Q

What is lysogeny?

A

Integration of vDNA into bDNA/chromosome

105
Q

How is lysogeny carried out?

A

via nonhomologous recombination

106
Q

What is formed because of lysogeny?

A

Latent prophage

107
Q

What is the result of lysogenic conversion?

A

Bacterial cell becomes lysogen

108
Q

What becomes of a latent prophage?

A

Replication of this viral DNA with the bacterial host DNA so all the daughter cells carry it

109
Q

What can happen to the latent prophage?

A

If stress occurs (ie. UV light, temp, nutrients etc.) lytic cycle can be activated. If the prophage has a virulent gene this will then make the bacteria a pathogen.

110
Q

What were three examples of pathogenic lysogens in the lecture?

A

Hemorrhagic diarrhea
Botulism
Diphtheria

111
Q

What is specialized transduction?

A

Very rare but during stress-induced lytic cycle prophage is incorrectly excised from bDNA and now has segments of bDNA + vDNA.

112
Q

What is a defective phage?

A

Machinery packs capsids with vDNA + bDNA

Lytic cycle releases these and they are spread via nonhomologous recombination

113
Q

What are not replicons?

A

IS + Tn + PAI

114
Q

What does PAI stand for?

A

Pathogenicity Island

115
Q

What is the simplest form of MGE?

A

Insertion sequence

116
Q

What does an IS contain?

A

Inverted repeats on ends

Transposase gene for integration into replicon w/ no additional coding

117
Q

How is an IS inserted?

A

Via nonhomologous method into a specific sequence - creates direct repeats upon insertion

118
Q

Where does a Tn transfer?

A

transfers DNA within a cell from one position to another
chromosome to plasmid
plasmid to plasmid

119
Q

What is the structure of a Tn?

A

2 insertion sequences + central region

120
Q

What is contained on the central region of a Tn?

A

AB resistance + toxin genes

121
Q

What can be the results of the nonhomologous recombination with a Tn?

A

Can insert into an inactive gene on chromosome or plasmid and aid bacteria in being more virulent or resistant

or can insert into a essential protein and cause cell death

122
Q

What is a PAI?

A

unusual clusters of genes, that insert tRNA or tRNA-like genes into bacterial chormosome

123
Q

What do PAI encode for?

A

Virulence factors such as toxins + AB resistance

124
Q

How is a PAI inserted into the genome?

A

Nonhomologous recombination

125
Q

Why are PAI’s unstable?

A

Different %G+C that parent DNA - implies foreign source to DNA
Overtime breaks down, lost from genome
Not seen in nonpathogenic forms of species

126
Q

What is clinically important to remember about PAI’s?

A

Can cause different pathogens even if the bacteria are from the same species

127
Q

What is structure is adding to the spread of AB resistance?

128
Q

What is an integron?

A

Genetic element that allows for efficient capture and expression of exogenous genes

Bacteriology (28 decks)

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