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MICROBIOLOGY: CMOD-Week 1 > (03) Prokaryotic Genetics > Flashcards

(03) Prokaryotic Genetics Flashcards

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1
Q

T or F: bacteria only encode a single RNA polymerase

A

True

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2
Q

What is an operator?

- location relative to promoter.

A

Operator:
- Binds Proteins in involved in gene expression

  • Located near the promoter
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3
Q

Why can transcription be paired with translation in bacteria?

A
  1. No Introns

2. No Nucleus

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4
Q

What is an operon?

- what bacterial type contains the lac operon?

A
  • Cluster of Genes involved in a related function that is transcribed on a single mRNA (aka polycistronic)

Gram (-) bacillus Escherichia Coli

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5
Q

What 3 genes make up the lac operon?

  • what is its function?
  • Does gene transcription take place in unison or individually?
A
  1. Lac Z –> ß-galactosidase
  2. Lac Y –> Lactose Permease
  3. Lac A –> Lactose Transacetylase
  • Allows Gram (-) Bacillus Escherichia Coli to use lactose
  • Transcrption takes place together but RNA translation takes place individually

**Note: if this was not the case, then they would be translated together then cleaved apart

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6
Q

What are the reasons for an operon rather than genes located on different parts of the chromosome?

A
  1. Operons help to ward off loss of function
    - if genes were in different part of the genome they could more easily be lost by evolutionary divergence
  2. Use of a single promoter and operator provides co-regulation of genes in the operon. ALLOWS FOR COORDINATED EXPRESSION
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7
Q

What are the 3 types of gene regulation?

  • which type is most rare?
  • why?
A
  1. Constitutive
    - no regulation, genes always expressed
    * *Most rare because of ATP expenditure
  2. Positive Regulation
    - Activator Protein promotes RNA polymerase binding to promoters
  3. Negative Regulation
    - Repressor protein binds operator sequence and prevents transcription until it is removed
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8
Q

Is positive or negative regulation more common?

- why?

A

Negative regulation

  • From an evolutionary standpoint loss of promoter leads to complete loss of the gene while loss of repressor, then the gene is still functional
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9
Q

What is a regulon?

A

Independently transcribed genes or multiple operons are controlled by the same regulator protein = Regulon

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10
Q

Steps of 2 component signaling?

A
  1. Extracellular Molecule Binds Receptor in membrane = SENSOR that has an intracellular TRANSDUCER
  2. SENSOR then TRANSDUCER get phosphorylated
  3. TRANSDUCER works on operator

***Important in Quorum Sensing

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11
Q

What processes use 2 component signaling?

A
  1. Changing Temperature
  2. Osmolarity
  3. Extracellular Iron availability
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12
Q

What is quorum sensing?

- what virulence factor relies on this hardcore?

A
  • Bacteria Communication via releasing and measuring signaling molecules
  • More signaling molecules released as population grows until CONCENTRATION THRESHOLD is reached
  • All cells now begin expressing new gens

**Particularly important in biofilm formation

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13
Q

What are the signaling molecules in quarum sensing?

A
  • Non-peptides

- Usually cyclic structures like lactones or quinolones

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14
Q

What challenges are posed to bacteria as a result of them being haploid?
- How are these challenges overcome?

A
  1. Mutations readily lead to LOSS of FUNCTION
    - Overcome by SHEER NUMBERS, loss of millions of bacteria doesn’t matter much
  2. Phenotypic Diversity could be limited because of only a single pair of alleles
    - Phase Variation
    - Antigenic Variation
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15
Q

What is phase variation?

- what is the consequence of phase variation?

A

a. Gene can be inverted into the ON position
- aka Aligned with its promoter

b. Gene could be inverted into OFF position
- aka Gene FLIPPED so that PROMOTER IS NOT LONGER ALIGNED WITH GENE

**Results in an on and off switch for the gene

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16
Q

Antigenic Variation

  • what is the overall result
  • what bacteria is known to use this?
  • what is the clinical presentation for antigenic variation?

**SEE SCHEME for STEPS

A

Bacteria:
- Neisseria Gonorrheae

Overall Result:
- Large array of Surface Components

  • Recurring infection because they are constantly changing their pilus
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17
Q

Requirements for Antigenic Variation?

A
  • Large numbers of bacteria
  • Lots of growth

**Because you need functional mutant to expand and take over

18
Q

What are 4 ways that bacteria can actually acquire new genes?

A
  1. Transposition
  2. Conjugation
  3. Transduction
  4. Transformation
19
Q

What is transposition?

- 4 basic elements?

A
  • Genetic elements hop or put an additional copy of themselves into their genome
  • *All happens in one cell, does not jump from one to the next
  1. Insertion sequences
  2. Transposase
  3. Repressor
  4. Beneficial host gene (ANTIBIOTIC RESISTANCE GENE)
20
Q

What are the functions of the 4 basic transposon elements?

A
  1. Insertion Sequences
    - Inverted DNA repeats
  2. Transposase
    - Recombinase that allows insertion of sequence
  3. Repressor
    - Regulates frequency of Transmission
  4. Beneficial Host Gene
    - Antibiotic Resistence Gene
    - other virulence factor gene
21
Q

How can transposons be detrimental to cell health?

A
  • It could enter in a bad spot in the genome (e.g. before lacZ)
  • Must insert before a gene

**Cause problems when they bind to genes or operons

22
Q

What two ways do transposons increase cell diversity?

A
  1. Introduction of an antibiotic resistance gene or another gene
  2. Creation of mutants lacking non-essential wild-type functions

**all others will die

23
Q

Plasmids

  • what are they?
  • How big are they?
  • Gene types?
A

Plasmids - Extrachromosomal (episomal) circular DNAs found in MOST bacteria

2-500 kilobase pairs

Targets for antibiotic genes for transposons

24
Q

T or F: smaller plasmids can replicated independently of the genome

A

True

25
Q

Why are plasmids maintained in the genome if they don’t contain genes needed for cell survival?

A
  • They many have transposons in them that contain Antibiotic Resistance Genes
26
Q

While transposons in themselves are retained to the cell from which they orginated, how could they travel to another cell?

A
  • Could go to another cell via a Plasmid during Conjugation
27
Q

Conjugation

  • how does it occur
  • how is genetic diversity conferred as a result?
A

How:
- High Frequency Transfer (Hfr) or F+ cells transfer F factor plasmid from one cell to another that is F- via a sex pilus

Genetic Diversity:

  • Results from the fact that genomic DNA can enter off of chromosomes that are Hfr that allow some of their own genetic material to enter the second cell.
  • Cell2 can either put Hfr into genome or make a T or R factor plasmid
28
Q

What are PAIs (pathogenicity-associated islands)?

- what leads to their formation?

A
  • Large regions of a chromosome that encode various virulence factors, toxins, and iron acquisition components.
  • Hfr are believed to be the major source of PAIs
29
Q

What are two factors that help us to know that PAIs are from an external source?

A
  1. NON-pathogenic strains of the same bacterium lack PAIs

2. Also lack G+C

30
Q

What is the difference between an F factor and an R factor?

A

F Factor:
- plasmid that does not contain resistance genes

R Factor:
- plasmid that has acquired antibiotic resistance genes LIKELY FROM A TRANSPOSON

31
Q

Given that F factor is needed for formation of the sex pilus, how can R factor spread?

A
  1. R Factor may be conjugative (can form the pilus)

OR

  1. It may be dependent on F factor for conjugation
32
Q

What is the major thing that confers antibiotic resistance of bacteria, and why is this?

A
  • R Factor

why?
- It can spread through intERspecies conjugation and sometimes even across genera

**Bacteria with several different R factors may confer multidrug antibiotic resistance

33
Q

What are viruses called that prey on bacteria?

  • what are the two types?
  • how do they differ?
A
  • Phage
  1. Lytic
    - Phage infects –> Replicates –> released from cell (usually by lysis)
  2. Lysogenic (temperate)
    - Phage genomes integrate at specific sites in the bacterial chromosome (aka lysogen)
  • Lysogen remains in the cell until the cell undergoes stress (radiation etc.)
  • Stress induces Lytic Replication
34
Q

What is transduction?

- what processes can cause transduction?

A
  • Transfer of genes from bacteria 1 (host) to bacteria 2 via a phage
  • Phages moves from one cell to the next causes this
35
Q

Generalized Transduction

  • who carries it out
  • how
  • what are the consequences
A

(transfer of genes horizontally among bacteria via phage)

  • ONLY carried out by LYTIC phage

How:
1. Lytic phage cleaves bacterial chromosome into small fragments

  1. Fragments may be similar size as virus (phage) genome and packages into Phage Particles
  2. Phage particles containing Bacteria 1 DNA will be inserted into Bacteria 2

Consequences:
- Any bacterial gene can be transduced to a recipient cell (resistance genes may be passed along)

36
Q

Specialized Transduction

  • who carries it out
  • how
  • what are the consequences
A
  • Carried out by Temperate (lysogenic) phages

How:
- lysogen (viral genome) is inserted into the host genome

  • when stress occurs ABERRANT EXCISION causes some of the viral DNA to be left behind and BACTERIAL DNA is included instead
  • New phage is stable and will continue to carry bacterial DNA with it

Consequences:
**Original lysogen only inserts at certain parts of the genome, therefore only a few specific bacterial genes can be transduced by any particular phage

37
Q

Of the two types of transduction, which is most important to generating genetic diversity?

A

Specialized transduciton

38
Q

What is transformation?
- what is its role in nature
- what are cells called that can carry out transformation?
Example?

A
  • Uptake of Naked DNA from one cell to another
  • Insignificant role in creating genetic diversity in nature
  • Cells that can carry out transformation = Competent
  • e.g. Streptococcus Pneumoniae
39
Q

Overall, what is the most common way that bacteria exchange information?

A

Conjugation

40
Q

What is the paradigm case of transduction?

- what type?

A

Cholera Toxin (specialized transduction)

41
Q

What is the rate of both generalized and specialized transduction?

A

1/1000 - 1/10,000

42
Q

What is the rate of antigenic variation?

A

1/1000

MICROBIOLOGY: CMOD-Week 1 (10 decks)

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