BIO 353 COMPREHENSIVE EXAM 2026 QUESTIONS AND
ANSWERS GRADED A+
✔✔What role does the sensor kinase play in the two-component system? - ✔✔It senses
external signals and can phosphorylate itself.
✔✔What happens when the competence factor binds to the two-component system? -
✔✔The sensor kinase phosphorylates itself and transfers phosphate to the response
regulator, ComE.
✔✔What is the function of sigma factors in bacterial transcription? - ✔✔They act as
subunits of RNA polymerase, directing it to specific promoter sites on DNA.
✔✔What is the significance of high cell density in bacterial signaling? - ✔✔It triggers the
binding of competence factors to the two-component system, leading to gene
transcription changes.
✔✔What is Autoinducer AI-1? - ✔✔An intra-species signaling molecule used by Vibrio
harveyi, synthesized by LuxLM.
✔✔What is the role of LuxN in the signaling pathway? - ✔✔It is a sensor kinase that
senses Autoinducer AI-1 and gets phosphorylated.
✔✔What is the function of LuxO in the signaling pathway? - ✔✔It is a transcription
factor that expresses Qrr small RNAs, inhibiting LuxR mRNA translation.
✔✔What happens to LuxR mRNA when Qrr small RNAs are expressed? - ✔✔LuxR
mRNA is inhibited, preventing the production of luciferase and virulence factors.
✔✔What is Autoinducer AI-2? - ✔✔An inter-species signaling molecule that can be
sensed by multiple bacterial species.
✔✔What is the role of LuxS in bacterial communication? - ✔✔It synthesizes
Autoinducer AI-2, facilitating interspecies communication.
✔✔What is the 'universal language' in bacterial communication? - ✔✔The concept that
Autoinducer AI-2 can be used by various bacterial species for signaling.
✔✔How do bacteria control interspecies communication? - ✔✔By using systems like the
Lsr system in E. coli to take up AI-2 and prevent signaling.
✔✔What are AHL lactonases? - ✔✔Enzymes produced by some bacteria that target
and break down AHL signals used in intraspecies communication.
, ✔✔What is the significance of the Methyl Cycle in bacteria? - ✔✔It is involved in basic
metabolism and the production of Autoinducer AI-2 through LuxS.
✔✔What is the relationship between LuxR and luciferase production? - ✔✔LuxR
activates the luxCDABE genes, leading to luciferase production and bioluminescence.
✔✔What is the role of small RNAs in the LuxR signaling pathway? - ✔✔They inhibit
LuxR mRNA, preventing the translation of proteins that promote bioluminescence.
✔✔What is the function of the LuxQ sensor kinase? - ✔✔It senses Autoinducer AI-2
and regulates gene expression based on its concentration.
✔✔What happens when AI-1 concentration is low? - ✔✔The sensor kinase remains
active, leading to the expression of small RNAs that inhibit LuxR.
✔✔What is the effect of high AI-1 concentration on the sensor kinase? - ✔✔It binds AI-
1, shutting off the sensor kinase and preventing phosphorylation of LuxU and LuxO.
✔✔What are the implications of signal interference in bacterial communities? -
✔✔Bacteria can disrupt communication, affecting competition and cooperation within
polymicrobial communities.
✔✔What is the role of archaeal quorum sensing? - ✔✔Some archaea may use unique
signaling molecules for communication, but lack LuxS homologs.
✔✔How do sulfur-reducing bacteria interfere with Gram-negative signaling? - ✔✔They
produce AHL lactonases that can disrupt intraspecies signaling among Gram-negative
bacteria.
✔✔What is the primary purpose of the CRISPR/Cas system in bacteria? - ✔✔To
provide adaptive immunity against invasive genetic elements from foreign plasmids or
bacteriophages.
✔✔What is the purpose of restriction modification systems in bacteria? - ✔✔To protect
against foreign DNA from phage genomes or plasmids, providing innate (non-adaptive)
defense.
✔✔What are the major components of the CRISPR/Cas system? - ✔✔CRISPR array,
cas genes, CRISPR RNAs (crRNAs), and tracrRNA.
✔✔What are the major steps in the CRISPR/Cas defense process? - ✔✔Adaptation
(Spacer Acquisition), Expression (crRNA Biogenesis), and Interference (Target
Recognition and Destruction).
ANSWERS GRADED A+
✔✔What role does the sensor kinase play in the two-component system? - ✔✔It senses
external signals and can phosphorylate itself.
✔✔What happens when the competence factor binds to the two-component system? -
✔✔The sensor kinase phosphorylates itself and transfers phosphate to the response
regulator, ComE.
✔✔What is the function of sigma factors in bacterial transcription? - ✔✔They act as
subunits of RNA polymerase, directing it to specific promoter sites on DNA.
✔✔What is the significance of high cell density in bacterial signaling? - ✔✔It triggers the
binding of competence factors to the two-component system, leading to gene
transcription changes.
✔✔What is Autoinducer AI-1? - ✔✔An intra-species signaling molecule used by Vibrio
harveyi, synthesized by LuxLM.
✔✔What is the role of LuxN in the signaling pathway? - ✔✔It is a sensor kinase that
senses Autoinducer AI-1 and gets phosphorylated.
✔✔What is the function of LuxO in the signaling pathway? - ✔✔It is a transcription
factor that expresses Qrr small RNAs, inhibiting LuxR mRNA translation.
✔✔What happens to LuxR mRNA when Qrr small RNAs are expressed? - ✔✔LuxR
mRNA is inhibited, preventing the production of luciferase and virulence factors.
✔✔What is Autoinducer AI-2? - ✔✔An inter-species signaling molecule that can be
sensed by multiple bacterial species.
✔✔What is the role of LuxS in bacterial communication? - ✔✔It synthesizes
Autoinducer AI-2, facilitating interspecies communication.
✔✔What is the 'universal language' in bacterial communication? - ✔✔The concept that
Autoinducer AI-2 can be used by various bacterial species for signaling.
✔✔How do bacteria control interspecies communication? - ✔✔By using systems like the
Lsr system in E. coli to take up AI-2 and prevent signaling.
✔✔What are AHL lactonases? - ✔✔Enzymes produced by some bacteria that target
and break down AHL signals used in intraspecies communication.
, ✔✔What is the significance of the Methyl Cycle in bacteria? - ✔✔It is involved in basic
metabolism and the production of Autoinducer AI-2 through LuxS.
✔✔What is the relationship between LuxR and luciferase production? - ✔✔LuxR
activates the luxCDABE genes, leading to luciferase production and bioluminescence.
✔✔What is the role of small RNAs in the LuxR signaling pathway? - ✔✔They inhibit
LuxR mRNA, preventing the translation of proteins that promote bioluminescence.
✔✔What is the function of the LuxQ sensor kinase? - ✔✔It senses Autoinducer AI-2
and regulates gene expression based on its concentration.
✔✔What happens when AI-1 concentration is low? - ✔✔The sensor kinase remains
active, leading to the expression of small RNAs that inhibit LuxR.
✔✔What is the effect of high AI-1 concentration on the sensor kinase? - ✔✔It binds AI-
1, shutting off the sensor kinase and preventing phosphorylation of LuxU and LuxO.
✔✔What are the implications of signal interference in bacterial communities? -
✔✔Bacteria can disrupt communication, affecting competition and cooperation within
polymicrobial communities.
✔✔What is the role of archaeal quorum sensing? - ✔✔Some archaea may use unique
signaling molecules for communication, but lack LuxS homologs.
✔✔How do sulfur-reducing bacteria interfere with Gram-negative signaling? - ✔✔They
produce AHL lactonases that can disrupt intraspecies signaling among Gram-negative
bacteria.
✔✔What is the primary purpose of the CRISPR/Cas system in bacteria? - ✔✔To
provide adaptive immunity against invasive genetic elements from foreign plasmids or
bacteriophages.
✔✔What is the purpose of restriction modification systems in bacteria? - ✔✔To protect
against foreign DNA from phage genomes or plasmids, providing innate (non-adaptive)
defense.
✔✔What are the major components of the CRISPR/Cas system? - ✔✔CRISPR array,
cas genes, CRISPR RNAs (crRNAs), and tracrRNA.
✔✔What are the major steps in the CRISPR/Cas defense process? - ✔✔Adaptation
(Spacer Acquisition), Expression (crRNA Biogenesis), and Interference (Target
Recognition and Destruction).
