Micro: Bacterial Genetics Flashcards

1
Q

Describe the function of the operator located near the promotor upstream of the gene to be transcribed in prokaryotic DNA.

A

A sequence that binds protein involved in the regulation of the gene’s expression.

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2
Q

True of false: Prokaryotic genes have introns.

A

False

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3
Q

True of false: transcription and translation happen independently in prokaryotes.

A

False, they are coupled due to lack of nucleus and absence of introns in genes.

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4
Q

Describe the function of an operon.

A

A cluster of genes, typically involved in a related function, that are transcribed on a single mRNA, and are then translated independently to produce the individual proteins.

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5
Q

What is/are the purpose(s) of clustering functionally related genes into operons?

A
  1. Operons help to ward off loss of function b/c if genes contributing to a single process reside in different regins of the genome, they can be more easily lost to evolutionary divergence.
  2. Use of a single promotor and operator provides co-regulation of the genes in the operon, fascilitating expression of the functionally-related genes.
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6
Q

List the 3 types of gene regulation in bacteria.

A

Constitutive
Positive
Negative

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7
Q

What occurs in Constitutive gene regulation?

A

effectively no regulation, genes are always expressed.

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8
Q

What occurs in positive gene regulation?

A

Activator protein promotes RNA polymerase binding to promoters and therefore facilitates expression.

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9
Q

What occurs in negative gene regulation?

A

Repressor protein binds the operator sequence and prevents transcription by RNA polymerase until the repressor is removed.

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10
Q

Is constitutive gene regulation common? Why or why not?

A

No, it is rare because of the amount of energy expended in constantly expressing genes.

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11
Q

What do inducers do?

A

Interact with either activators for + regulation or repressors for - regulation.

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12
Q

When independently transcribed genes, or multiple operons, are controlled by the same regulatory protein or process, they are considered to constitute a:

A

regulon (as opposed to an operon)

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13
Q

Please describe the two-component signaling pathway.

A

A ligand binds to a sensor on the cytoplasmic membrane. This sensor is phosphorylated which causes a transducer (intracellular) to be phosphorylated. The transducer will then function as an activator and bind the operator of genes whose expression will lead to an appropriate response to the extracellular ligand.

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14
Q

List a few environmental conditions that necessitate the two-component signaling pathway.

A

changes in temperature, osmolarity, or availability of extracellular iron.

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15
Q

What is the key difference between the Lac operon regulation and the two-component signaling pathway?

A

In the Lac operon, allolactose must be brought intracellularly to bind to the repressor, releasing it from the operator. In the two-component signaling pathway, there is an extracellular sensor that binds an extracellular ligand and then transmits the signal intracellularly.

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16
Q

Describe quorum sensing and why it is important. Please, sir.

A

The ability of a cell (bacterium) to sense cell density by receiving signal molecules from surrounding cells.
Used to coordinate the expression of virulence genes needed to escape the immune response. Also especially important in biofilm formation.

17
Q

What challenges are presented by a bacterial genome being haploid?

A
  1. mutations readily lead to loss of function since no back-up
  2. phenotypic diversity limited in absence of allelic pairs
18
Q

How do bacteria overcome the challenges associated with having a haploid genome?

A

New variants of the pilus protein that evade the immune response and re-establish infection. (antigenic variation)

19
Q

Describe the clinical presentation of antigenic variance.

A

Recurring infection due to tricking the immune system into believing it is a new threat. Immune system has to start over from innate immune response, develop new Abs, etc.

20
Q

List the 4 methods of genetic exchange among bacteria.

A
  1. transposition
  2. conjugation
  3. transduction
  4. transformation
21
Q

Describe transposons and their involvement in transposition.

A

Mobile genetic elements that are said to “hop” from one site in a genome to another.

22
Q

Which element of the transposon ensures that the transposon is conserved from one generation of bacteria to the next?

A

Most benefit the host (increasing fitness) by encoding a virulence factor or antibiotic resistance gene. This helps ensure that that particular strain survives to replicate and is thus found in subsequent generations.

23
Q

What is a downside inherent to the action of transposons?

A

Transposons actually function as mutagens and can disrupt normal transcription and translation with moving about in the genome.

24
Q

Can transposons simply “hop” from one bacterium to another?

A

No.

p.s.- You’re doing great! Keep up the good work!

25
Q

Describe conjugation among bacterial populations.

A

A mating process in which a donor bacterium containing an F (fertility factor), which is essentially the gene for a bacterial penis, makes contact with a non F+ bacterium and transmits its F factor gene to the receiving cell, thus conferring the ability to eFF to the new cell. Along with the F factor, some of the donor’s genome may also be transferred. BOOM diversity.

26
Q

What is a plasmid?

A

An extrachromosomal, double-stranded circular DNA found in most bacteria.

27
Q

Can plasmids replicate independently from the bacterial genome?

A

Yes, to increase copy number.

28
Q

How can plasmids’ presence be maintained within a cell?

A

Transposons, conferring antibiotic resistance that benefits the host cell.

29
Q

What the F*&# are Hfr cells?

A

Bacteria that can now F&# because they were F&#ed by F+ bacteria. Try forgetting that shit.

30
Q

What are pathogenicity-associated islands (PAIs)?

A

Large regions of a chromosome that encode various virulence factors such as type III secretion systems, toxins, and iron acquisition components.

31
Q

If a plasmid acquires an antibiotic resistance gene, it is termed:
Where did it most likely get this gene?

A

an R-plasmid (factor); a transposon

32
Q

Why are R-factors (R-plasmids) significant?

A

Major reason for the spread of abx resistance and multi-drug resistance.

33
Q

What is a bacteriophage?

A

A virus that preys on bacteria

34
Q

What are the two general categories of phages?

A

Lytic- replicate within cells, lyse cells
Lysogenic/Temperate- incorporate genome (lysogen) into bacterial genome, lysogen replicates as part of bacterial chromosome until stress to cell lyses cell

35
Q

What is transduction?

A

When genetic material from one bacterium is inadvertently transferred to another via phage.

36
Q

Describe generalized transduction and how it occurs.

A

Carried out by strictly lytic phages only.
Lytic phage cleaves bacterial chromosome into small fragments. Fragments of bacterial DNA accidentally (1/1000 baby phages) packaged into new baby phages that go on to infect new bacteria and incorporate the donor bacterium’s DNA into the new host bacterium’s genome. Can happen only once because no phage DNA transduced! BOOM (poor) diversity.

37
Q

Describe specialized transduction and how it occurs.

A

Temperate/Lysogenic phage undergoes an aberrant excision and mistakenly incorporates an adjacent bacterial gene into the baby phage. New, stable temperate phage results, followed by re-infection of new bacteria over and over, always transducing the acquired bacterial gene. BOOM (better) diversity.

38
Q

Describe bacterial transformation.

A

Bacterium eats free floating DNA in environment and incorporates it into its genome. Plays an insignificant role in genetic diversity in nature.

39
Q

Which form of genetic exchange plays the most significant role in genetic diversity?

A

Conjugation 25-50% of chromosome transferred. Followed by transformation with 5-10% of chromosome transferred.