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Microbiology > Microbial Genetics > Flashcards

Microbial Genetics Flashcards

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1
Q

What is the diference between a mutation and a mutant?

A
  1. Mutation - HERITABLE change in DNA sequence that can lead to a change in phenotype
  2. Mutant - a strain of any cell of virus differing from parental strain in a genotype (nucleotide sequence of genome)
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2
Q

Will a mutation always results in a change in the phenotype?

A
  • Yes. that is the definition of a mutation.
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3
Q

What is a selectable mutation?

A
  • give mutants a growth advantage under certain conditions
  • Usefule in genetic research
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4
Q

What is a nonselectable mutation?

A
  • Usually has neither an advantage nor a disadvantage over the parent
  • Doesnt effect growth
  • Based on appearance - color, hair etc…
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5
Q

What is the difference between spontaneous mutation and induced mutation?

A
  • Spontaneous
    • Mutation that occurs without external intervention
    • Inherent mistakes made by polymerases during genome replication
  • Induced
    • mutations made environmentally or deliberately
    • could results from exposure to natural radiation, or oxygen radicals
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6
Q

Point Mutations:

  1. Change only [] base pair
  2. Can lead to single [] [] change in a protein, an incomplete protein, or [] change at all
  3. Can lead to [], [], or [] mutations (occuring within the coding region)
A
  1. 1 base pair
  2. amino acid change, or no change
  3. silent, missense, or nonsense
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7
Q

Would a mutation in DNA have larger effect in bacteria or eukaryotes?

A
  • Bacteria - they are haploid and have a smaller genome with less non-coding genes
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8
Q

What is the difference between:

Silent Mutation, Missense Mutation, Nonsense Mutation?

Where does these 3 types of mutations occur on a gene?

A
  1. Silent - different base pair at DNA/RNA level compared to the wild type. Not change in proteins though
  2. Missense - Change in a base pair that results in a change of a codon that codes for a different amino acid. Final structure of protein doesnt matter.
  3. Nonsense - addition of stop codon prematurely
  4. These occur in coding regions.
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9
Q

What is a frameshift mutation?

A
  • small deletion or insertion that results in a shift in the reading frame.
    • Typically occur in coding region and typically single base insertion/deletion
  • +1 = insertion
  • -1 = deletion
  • Often results in complete loss of gene function
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10
Q

What type of double frameshift mutation can be “ok?”

+/-, +/+, or -/-

What type of triple frameshift mutation can be “ok?”

+/+/+ or -/-/-

A
  1. +/- can sometimes be ok. If the two mutations are near by
  2. +/+/+ or -/-/-…could be ok because it basically adds or subtracts a single amino acid to the protein. Better if close together again.
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11
Q

What are Transposable Elements?

A
  • discrete segments of DNA that move as a unit from one location to another within other DNA molecules
  • Found in all 3 domains of life
  • Move by process called transposition
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12
Q

What are the 2 main types of transposable elements in bacteria?

A
  • Transposons and Insertion Sequences
    • both carry genes encoding transposase
    • both have inverted repeats at tehir and
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13
Q

What is transposase?

A

enzyme that helps mobile DNA elements cut out and then transport to new DNA site.

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14
Q

Insertion Sequences Facts:

  1. [] transposable element
  2. ~[] nucleotides long
  3. The [] gene is sandwhiched between 2 [] []
    1. this is its only coded gene
  4. Found in [] and chromosomes of [], [] and a few viruses
A
  1. simplest
  2. 1,000
  3. transposase gene, inverted repeats
  4. plasmids, bacteria, archea, and a few viruses
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15
Q

Transposons Facts:

  1. Has additional [] genes between the inverted repeats
    1. may include [] [] genes
  2. Transposase recognizes [] and cuts out transposon, moves to new [] [] , and re-inserts it
A
  1. accessory
    1. antibiotic resistance
  2. IRs, target site
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16
Q

What is the differene between a Transition Mutation and a Transversion Mutation?

A
  1. Transition - C <–> T or A<–>G
    1. Purine to purine or pyrimidine to pyrimidine
  2. Transversion - C/T <–> A/G
    1. Interchange of purines and pyrimidines
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17
Q

What would be worse?

Mutation in catalytic Site and structural site vs non-important site?

Early Frameshift vs Late Frameshift?

A
  • Depends on where. Not all mutations are equal.
  • clearly a mutation in the catalytic site could be worse than a non important site
  • An early frameshit could result in an incomplete or faulty protein, but a late frameshft may not even effect the function of a protein
18
Q

RNA viruses have a large error rate in terms of spontaneuous mutations.

Why is this and how could it be advantageous?

A
  • RNA polymerases dont have proofreading
  • Viruses us this to continually adapt and evolve
19
Q

What is a mutagen?

A
  • Chemical, physical, or biological agent that increases mutation rates
20
Q

What are several classes of chemical mutagens?

A
  1. Nucleotide Base Analogs - resemble nucleotides
  2. Chemical Mutagens that induce chemical modifications
    1. alkylating agents like nitrosoguanidine
  3. Chemical mutagens that ause frameshift mutations
    1. intercalating agents like acridines
21
Q

What is an example of an alkylating mutagen?

What is an example of an intercalating agent mutagen?

A
  1. Nitrosoguanidine
  2. Acridines
    1. can create an insertion/deletion that leads to a frameshift
22
Q

What are the 2 main categories of mutagenic electrogmagnetic radiation?

A
  1. Non-ionizing (UV radiation)
    1. Pyrimidine dimer can results from this
  2. Ionizing (X-ray, cosmic rays, gamma rays)
    1. ionizes water and produce free radicals
    2. Free radicals damage macromolecules in the cell.
23
Q

Can a cell repair itself after a transposon or virus has been added to the genome?

A
  • No
  • However, repair mechanisms exist for chemically or physically derived mutations.
24
Q

What are the different biological mutagens?

A
  1. Transposons
  2. Viruses
    1. can insert viral genomes into host chromosomes
  3. Bacteria
    1. produce reactive oxygen and nitrogen species that act as ionizing radiation
25
Q

DNA Repair Mechanisms and Associated Enzymes for single strand break repair

  1. Base Excision Repair
  2. Mismatch Repair
  3. Nucleotide Excision Repair
A
  • Base Excision Repair (Single strand break repair)
    • DNA glycosylase recognizes wrong base, AP Endonuclease clips the wrong base out
  • Mismatch Repair (Single strand break repair)
    • Mut System - helps cut away the backbone
    • Ocurs after replication infidelity
  • Nucleotide Excision Repair (single stand break repair)
    • Occurs because of UV light exposure
    • Uvr proteins fix it.
26
Q

DNA Repair Mechanisms and Associated Enzymes for Double stranded break, translesion repair

  1. Recombinational Repair
  2. Translesion Synthesis
A
  1. Recombinational Repair (double strand break repair)
    1. RecA helps break double stranded backbone
    2. Happens after X-Rays exposure
  2. Translesion Synthesis
    1. Occurs after UV light creates blocking legion
    2. DinB helps remove lesion.
    3. Error prone
27
Q

What is an error free mutation repair mechanism?

A
  • Nucleotide excision repair
  • UvrB recruited by UvrA and knock off RNAP
  • UvrC is then recruited (this has endonuclease activity)
  • UvrD removes single strand with mutation
  • DNAP Pol 1 and ligase fill in gap
28
Q

What type of repair is used when large scale DNA damage occurs?

A
  • SOS regulatory system
    • error prone
    • replication can proceed and cell can replicate, but errors are more likely
  • Translesion synthesis
    • allows DNA to be synthesized with no template
29
Q

SOS Reponse facts:

  • What is the repressor for the SOS?
  • Which, active enzyme degrades the repressor?
A
  1. LexA
  2. RecA
30
Q

Which polymerases attach any nucleotides during the error prone mechanism of mutation repaitr? What is this mechanism called?

A
  1. Pol IV and Pol V
  2. Translesion Synthesis
31
Q

What are the 3 methods for genetic exchange in bacteria?

A
  1. Transformation
  2. Conjugation
  3. Transduction
32
Q

Transformation info:

  1. 2 types
    1. [] and [] competency
  2. Natural Competent
    1. Requires [] [] proteins and nucleases
    2. Species can be [] competent
  3. Induced Competent
    1. Specifc procedure to make cells competent
    2. [], [] , [] are examples
A
  1. Naturally Competent and Induced Competent
  2. DNA binding proteins
  3. Naturally
  4. Electrical shock, heat shock, differeing salt concentrations
33
Q

[] is the mechanism of genetic transfer that involves cell-to-cell contact?

A

Conjugation

34
Q

Does a sex pilus actually transfer the genetic material from cell to cell?

A
  • No the sex pilus is retrated, bringing cells closer together.
  • Genetic material is transferred through a pore.
35
Q

What is the differene between and F+ and F- cell in conjugation?

A
  • F+ has the sex pilus capability and genetic material to transfer
  • F- does not
36
Q

What are the 2 modes of transduction?

A
  1. The transfer of DNA from one cell to another by bacteriophage
  2. Generalized Transduction (think Lytic Phage)
  3. Specialized Transduction (Think Lysogenic PHage)
37
Q

What is the difference between generalized transduction and specialized transduction?

A
  1. Generalized - DNA from any portion of the host genome is packaged inside the virion
  2. Specialized - DNA from a specific region of the host chromosome is integrated directly into the virus genome.
    1. DNA of a temperate virus excises incorrectly for example and takes adjacent host genes along with it.
38
Q

What is a transducing particle?

A
  • Phage with small bits of host DNA in the virion (comes from generalized transduction)
39
Q

Four fates of foreign DNA inside cells?

A
  1. Degraded by cellular enzymes
    1. RMS and CRISPR system
  2. Stable maintenance outside chromosome
    1. mainly plasmids
    2. Needs to have replication origins recognized by/compatbile with host
  3. “Random” insertion into genome
    1. Need to have special enzymes, not truly “random”
    2. Transposons and pathogenicity islands insert this way
  4. Site-specific recombination into genome
    1. need specific recognition site and recombinases
    2. Foreign DNA needs some similarity with host genome
    3. Integrates through homologous recombination
40
Q

What is homologous recombination?

A

Process that results in genetic exchange between similar DNA from two different sources

41
Q
A

Microbiology (11 decks)

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