Micro: Bacterial Genetics Flashcards
Describe the function of the operator located near the promotor upstream of the gene to be transcribed in prokaryotic DNA.
A sequence that binds protein involved in the regulation of the gene’s expression.
True of false: Prokaryotic genes have introns.
False
True of false: transcription and translation happen independently in prokaryotes.
False, they are coupled due to lack of nucleus and absence of introns in genes.
Describe the function of an operon.
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.
What is/are the purpose(s) of clustering functionally related genes into operons?
- 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.
- Use of a single promotor and operator provides co-regulation of the genes in the operon, fascilitating expression of the functionally-related genes.
List the 3 types of gene regulation in bacteria.
Constitutive
Positive
Negative
What occurs in Constitutive gene regulation?
effectively no regulation, genes are always expressed.
What occurs in positive gene regulation?
Activator protein promotes RNA polymerase binding to promoters and therefore facilitates expression.
What occurs in negative gene regulation?
Repressor protein binds the operator sequence and prevents transcription by RNA polymerase until the repressor is removed.
Is constitutive gene regulation common? Why or why not?
No, it is rare because of the amount of energy expended in constantly expressing genes.
What do inducers do?
Interact with either activators for + regulation or repressors for - regulation.
When independently transcribed genes, or multiple operons, are controlled by the same regulatory protein or process, they are considered to constitute a:
regulon (as opposed to an operon)
Please describe the two-component signaling pathway.
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.
List a few environmental conditions that necessitate the two-component signaling pathway.
changes in temperature, osmolarity, or availability of extracellular iron.
What is the key difference between the Lac operon regulation and the two-component signaling pathway?
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.
Describe quorum sensing and why it is important. Please, sir.
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.
What challenges are presented by a bacterial genome being haploid?
- mutations readily lead to loss of function since no back-up
- phenotypic diversity limited in absence of allelic pairs
How do bacteria overcome the challenges associated with having a haploid genome?
New variants of the pilus protein that evade the immune response and re-establish infection. (antigenic variation)
Describe the clinical presentation of antigenic variance.
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.
List the 4 methods of genetic exchange among bacteria.
- transposition
- conjugation
- transduction
- transformation
Describe transposons and their involvement in transposition.
Mobile genetic elements that are said to “hop” from one site in a genome to another.
Which element of the transposon ensures that the transposon is conserved from one generation of bacteria to the next?
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.
What is a downside inherent to the action of transposons?
Transposons actually function as mutagens and can disrupt normal transcription and translation with moving about in the genome.
Can transposons simply “hop” from one bacterium to another?
No.
p.s.- You’re doing great! Keep up the good work!
