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MD1 SF3 - EXAM 1 > Microbiologie: Génétique bactérienne > Flashcards

Microbiologie: Génétique bactérienne Flashcards

1
Q

What are the most important emerging infectious diseases globally?

A

Vancomycin-resistant S. aureus

Multidrug-resistant tuberculosis

Drug-resistant malaria

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2
Q

What are the three things a cell can change to become resistant to an antibiotic?

A
  1. Alteration of permeability
    1. Empêche pénétration
    2. Evacuation très rapide de l’antibiotique
  2. Modification or destruction of antibiotic
  3. Modification of the target (cible)
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3
Q

What are the primary targets of antibiotics within a cell?

A
  • Paroi
  • Synthèse des protéines (sous unité 50S ou 30S du ribosome)
  • Synthèse des protéines (elongation factor)

Best to target these as the processes are different than the ones in our own cells –> this won’t impact our cells only the bacterial ones

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4
Q

What are the differences between eucaryotic and bacterial cells?

A

These are the principal targets for antibiotics:

  • Cell wall not cell membrane
  • Nucleoid not nucleus (membrane)
  • Capsule
  • Flagellum
  • Ribosomes
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5
Q

What is the size of the genome of a single bacteria?

A

1.4 mm of DNA in a cell that 1-3µm –> very very compact

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6
Q

What does a small genome for a bacteria mean?

A

The smaller the genome (< 1.5) –> forces bacteria to depend on their host for reproduction… the bigger the bacteria, the more independent it can be

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7
Q

What is the difference between a chromosome and a plasmid?

A

Chromosome:

  • Circular
  • Contains factors for resistance, virulence and survival
  • Most bacteria only have one circular chromosome that contains around 2-3 million bp

Plasmid:

  • Extra genetic information that helps with resistance and virulence
  • Smaller than chromosomes varies between 1- 1000 kbp
  • Encode information that can be advantageous to the survival of a bacteria
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8
Q

What are the steps of binary fission?

A

New generation every 20 ish minutes:

  1. DNA replication
  2. Cell elongation
  3. Septum formation
  4. Completion of septum with formation of distinct walls
  5. Cell separation

Chromosome must be the same in both cells –> essential material for survival

BUT… plasmid replication and division is not as re

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9
Q

Why is bacterial gene expression regulated?

A

Goal: minimize energy expenditure

How: activating certain things only if needed

BUT should be able to produce what it needs to respond to things quickly

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10
Q

What is the most important type of regulation in bacteria?

A

Activators and repressors –> transcriptional regulation

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11
Q

What is the promoter?

A

Sequence typically referred to that’s right upstream or right next to where a gene is about to be transcribed. It’s the region where certain regulatory elements will bind; these are proteins that will bind to help RNA get transcribed

  • Recognized by RNA polymerase
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12
Q

What is the operator?

A

DNA sequences which signal the initiation of transcription when derepressed

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13
Q

What is a repressor?

A

Protein that inhibits the transcription of a gene (> 1 gene) by binding to the operator/promotor region

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14
Q

What is an activator?

A

Protein that stimulates transcription of a gene or more than one… generally recognize a specific sequence of DNA located near promotor region

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15
Q

What’s the difference between contrôle négatif and contrôle positif?

A

Positif: activator… inducible or repressible

Negative: repressor… inducible or repressible

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16
Q

How is tet**B regulated?

A

Tetracycline works as an inductor –> when it forms a complex with the repressor, it stops it from blocking the promotor –> now that the promotor is no longer obstructed by the repressor… RNA polymerase can produce mRNA

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17
Q

What is important to retain about bacterial regulation?

A
  1. Bacteria only produce certain proteins when they need them (to save energy)
  2. Regulation and autoregulation of these genes is usually an active process which means that the cell must always be in a metabolically active state
  3. Regulation usually comprises of multiple control loops
18
Q

What is simple regulation?

A

One promotor that controls one gene

19
Q

What is regulation in an operon?

A

One promotor that controls multiple adjacent genes

20
Q

What is regulation by a regulon?

A

One regulatory protein (repressor/activator) that controls multiple genes in multiple locations in the genome

21
Q

What is regulation by a stimulon?

A

Control of multiple nonadjacent genes by one stimulus

22
Q

What are the 4 kinds of mutation by modification of a sequence of DNA?

A
  1. Substitution: can be nonsense (early stop), silent (no change), or missense (change)
  2. Deletion (changes all nucleotides after it)
  3. Insertion (changes all nucleotides after it)
  4. Rearrangement (wrong order)

These mutations are transmitted to daughter cell and can be spontaneous or induced…

23
Q

What are spontaneous mutations?

A
  • errors during replication by DNA polymerase
  • random
  • not very frequent 10^-7 to 10^-11 per base pair
    • but billions of cells in colony so likelihood is quite high anyways
24
Q

What are induced mutations?

A
  • frequency much higher
  • caused by mutagenic agents such as:
    • physical, chemical, or biological agents
25
Q

What is the window of selectivity for mutations by antibiotics?

A

The concentration of antibiotics will affect the growth of susceptible bacteria in a population and resistant bacteria within this population

  • Suboptimal concentration of antibiotics during treatment can lead to the selectivity of resistant mutants leading to their growth and proliferation
  • There is still not enough information to conclude that antibacterial duration should be decreased yet…
26
Q

What are the five distinct groups of reparation systems for DNA within bacteria?

A
  1. Direct repair of DNA
  2. Repair by excision
  3. Repair by recombination
  4. SOS response –> can stimulate horizontal gene transfer
  5. Repair subject to errors –> can lead to mutation

certain antibiotics can activate these systems

27
Q

What are the three ways in which genes can be exchanged in bacteria?

A
  1. Transformation
  2. Conjugation
  3. Transduction
28
Q

How does transformation work?

A
  • Capacity for cells to be genetically modified by external DNA (called competency)
  • Can happen from a simple contact with DNA from other bacteria (they can be dead)
  • Will lead to the acquisition of new properties such as antibacterial resistance or virulence factors
  • Much more efficient between bacteria of the same species… not very effective between bacteria of different species
29
Q

How does conjugation work?

A

DNA is transferred from one bacterium to another. After the donor cell pulls itself close to the recipient using a structure called a pilus, DNA is transferred between cells. In most cases, this DNA is in the form of a plasmid.

  • Can happen between different species and even with more than 2 bacteria at a time
30
Q

How does transduction work?

A

Gene transfer mediated by bacteriophages

31
Q

What is a bacteriophage/phage?

A

virus that uniquely targets bacteria

32
Q

What is a capsid?

A

protein shell of a virus, enclosing its genetic material (DNA or RNA of phage)

33
Q

What are the three lifecycles of bacteriophages?

A
  1. Lytiques
  2. Lysogèniques
  3. Chroniques
34
Q

What is the lytic cycle?

A

Lytic cycle results in the destruction of the infected cell and its membrane.. releasing the DNA of the phage which was produced inside the bacteria

35
Q

What is the lysogenic cycle?

A
  1. The genetic material of the phage is integrated into the genetic material of the bacteria (circular chromosome)
  2. This material is then replicated with the material of the bacteria WITHOUT AFFECTING THE HOST CELL
  3. An event will cause the DNA of the phage to leave the chromosome of that bacteria
  4. New phages will be produced inside these cells and be liberated… lysing the cell and causing its death (​LYTIC)
36
Q

What is empaquetage accidentel?

A

When the genome of the host is packed into the phage:

Two kinds:

  1. Specialized: rare but can still propagate…
    • genome of phage is packaged with pieces of the host’s genome
  2. Generalized: more frequent but cannot propagate…
    • only the genome of bacteria is packaged into phage…
37
Q

What are the important genes transferred by transduction?

A
  • toxin of Corynebacterium diphteriae
  • enterotoxin of cerain forms of E. coli
  • toxin of streptocoque responsible for scarlatine
  • certain toxins of Clostridium botulinum
  • certain resistance genes to beta-lactamines in Pseudomonas
38
Q

What is transposition?

A

Movement of DNA segments inside one cell

  • chromosome position A to B
  • chromosome to plasmid
  • chromosome 1 to 2
  • chromosome to phage
  • plasmid to phage
  • plasmid A to B
  • phage A to B

requires intracellular proximity between locations where transfer is happening

39
Q

What are the different types of transposons?

A
  • Insertion sequence (IS) –> most simple transposons
  • Complex transposons –> IS + other genes
    • big importance medically because they can code for toxic or bacterial resistance genes in their central region
  • Transposable phages
  • Retrotransposons (RNA intermediate involved in transposition)
40
Q

What are intégrons?

A

Éléments génétiques qui recrutent des gènes de résistance et les intègrent les uns à la suite des autres devant des promoteurs forts assurant l’expression de multiples gènes simultanément

MD1 SF3 - EXAM 1 (11 decks)

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