BIO 353 FINAL EXAM 2026 ACTUAL QUESTIONS AND
ANSWERS GRADED A+
✔✔
✔✔What is an AHL lactonase and who produces it? - ✔✔An enzyme produced by
Bacillus species that breaks down AHL signals in Gram-negative bacteria.
✔✔What is an AHL acylase and which bacteria produce it? - ✔✔An enzyme made by
Pseudomonas aeruginosa that targets specific AHLs for intraspecies signaling.
✔✔What is social cheating in the context of quorum sensing? - ✔✔The phenomenon
where some bacteria, like Pseudomonas aeruginosa, benefit from the quorum sensing
of others without contributing.
✔✔What is quorum sensing in bacteria? - ✔✔A process where bacteria communicate
and coordinate behavior based on their population density.
✔✔What happens to bacteria when LasR is mutated? - ✔✔The bacteria lose virulence
and do not cause infection.
✔✔What is the role of autoinducers in quorum sensing? - ✔✔Autoinducers are small
molecules secreted by bacteria that accumulate and signal gene expression changes
when their concentration reaches a threshold.
✔✔What is the significance of Aliivibrio fischeri in relation to quorum sensing? -
✔✔Aliivibrio fischeri produces light in a mutualistic relationship with the Hawaiian bobtail
squid, which helps the squid avoid predation.
✔✔How do bacteria sense a quorum? - ✔✔Bacteria indirectly count cell numbers
through the accumulation of secreted autoinducers.
✔✔What are some processes controlled by quorum sensing? - ✔✔Bioluminescence,
virulence factor expression, competence for DNA uptake, biofilm production, and
antibiotic production.
✔✔What is transformation competence in Streptococcus pneumoniae? - ✔✔The ability
of bacteria to take up DNA from the environment and incorporate it into their genome.
✔✔What is the function of LuxI and LuxR in Aliivibrio fischeri? - ✔✔LuxI synthesizes the
AHL autoinducer, while LuxR is a receptor that binds AHL and regulates gene
expression.
, ✔✔What is the role of the competence factor (CF) in Gram-positive bacteria? - ✔✔CF is
an oligopeptide that acts as an autoinducer for interspecies communication and is
involved in transformation competence.
✔✔What occurs during the lag phase of bacterial growth? - ✔✔Bacteria adjust to their
environment without significant increase in number.
✔✔What characterizes the exponential growth phase in bacteria? - ✔✔Bacteria grow at
a constant rate, doubling in number at regular intervals.
✔✔What happens during the stationary phase of bacterial growth? - ✔✔The net number
of cells remains constant as waste accumulates and nutrients deplete.
✔✔What is the death phase in bacterial growth? - ✔✔Cells begin to die due to lack of
nutrients and accumulation of waste.
✔✔What is the relationship between cell density and AHL in Aliivibrio fischeri? -
✔✔High cell density leads to increased AHL concentration, which activates LuxR and
promotes the expression of luminescence genes.
✔✔What is the difference between intraspecies and interspecies communication in
bacteria? - ✔✔Intraspecies communication occurs between the same species, while
interspecies communication occurs between different species.
✔✔What is the significance of the Lux operon in Aliivibrio fischeri? - ✔✔The Lux operon
contains genes responsible for luciferase production, which is essential for
bioluminescence.
✔✔What is the role of membrane or cytoplasmic receptors in sensing autoinducers? -
✔✔These receptors detect autoinducers and initiate the corresponding gene expression
response.
✔✔What is AHL and its role in Gram-negative bacteria? - ✔✔AHL (N-acyl homoserine
lactone) is an autoinducer used for quorum sensing in Gram-negative bacteria,
including Aliivibrio fischeri.
✔✔What happens when AHL concentration is low in bacteria? - ✔✔There is insufficient
AHL to diffuse back into the cell and activate LuxR, preventing gene expression.
✔✔What is the function of ComB and ComA in Streptococcus pneumoniae? - ✔✔They
are part of a secretion system that helps in the uptake of DNA during transformation
competence.
ANSWERS GRADED A+
✔✔
✔✔What is an AHL lactonase and who produces it? - ✔✔An enzyme produced by
Bacillus species that breaks down AHL signals in Gram-negative bacteria.
✔✔What is an AHL acylase and which bacteria produce it? - ✔✔An enzyme made by
Pseudomonas aeruginosa that targets specific AHLs for intraspecies signaling.
✔✔What is social cheating in the context of quorum sensing? - ✔✔The phenomenon
where some bacteria, like Pseudomonas aeruginosa, benefit from the quorum sensing
of others without contributing.
✔✔What is quorum sensing in bacteria? - ✔✔A process where bacteria communicate
and coordinate behavior based on their population density.
✔✔What happens to bacteria when LasR is mutated? - ✔✔The bacteria lose virulence
and do not cause infection.
✔✔What is the role of autoinducers in quorum sensing? - ✔✔Autoinducers are small
molecules secreted by bacteria that accumulate and signal gene expression changes
when their concentration reaches a threshold.
✔✔What is the significance of Aliivibrio fischeri in relation to quorum sensing? -
✔✔Aliivibrio fischeri produces light in a mutualistic relationship with the Hawaiian bobtail
squid, which helps the squid avoid predation.
✔✔How do bacteria sense a quorum? - ✔✔Bacteria indirectly count cell numbers
through the accumulation of secreted autoinducers.
✔✔What are some processes controlled by quorum sensing? - ✔✔Bioluminescence,
virulence factor expression, competence for DNA uptake, biofilm production, and
antibiotic production.
✔✔What is transformation competence in Streptococcus pneumoniae? - ✔✔The ability
of bacteria to take up DNA from the environment and incorporate it into their genome.
✔✔What is the function of LuxI and LuxR in Aliivibrio fischeri? - ✔✔LuxI synthesizes the
AHL autoinducer, while LuxR is a receptor that binds AHL and regulates gene
expression.
, ✔✔What is the role of the competence factor (CF) in Gram-positive bacteria? - ✔✔CF is
an oligopeptide that acts as an autoinducer for interspecies communication and is
involved in transformation competence.
✔✔What occurs during the lag phase of bacterial growth? - ✔✔Bacteria adjust to their
environment without significant increase in number.
✔✔What characterizes the exponential growth phase in bacteria? - ✔✔Bacteria grow at
a constant rate, doubling in number at regular intervals.
✔✔What happens during the stationary phase of bacterial growth? - ✔✔The net number
of cells remains constant as waste accumulates and nutrients deplete.
✔✔What is the death phase in bacterial growth? - ✔✔Cells begin to die due to lack of
nutrients and accumulation of waste.
✔✔What is the relationship between cell density and AHL in Aliivibrio fischeri? -
✔✔High cell density leads to increased AHL concentration, which activates LuxR and
promotes the expression of luminescence genes.
✔✔What is the difference between intraspecies and interspecies communication in
bacteria? - ✔✔Intraspecies communication occurs between the same species, while
interspecies communication occurs between different species.
✔✔What is the significance of the Lux operon in Aliivibrio fischeri? - ✔✔The Lux operon
contains genes responsible for luciferase production, which is essential for
bioluminescence.
✔✔What is the role of membrane or cytoplasmic receptors in sensing autoinducers? -
✔✔These receptors detect autoinducers and initiate the corresponding gene expression
response.
✔✔What is AHL and its role in Gram-negative bacteria? - ✔✔AHL (N-acyl homoserine
lactone) is an autoinducer used for quorum sensing in Gram-negative bacteria,
including Aliivibrio fischeri.
✔✔What happens when AHL concentration is low in bacteria? - ✔✔There is insufficient
AHL to diffuse back into the cell and activate LuxR, preventing gene expression.
✔✔What is the function of ComB and ComA in Streptococcus pneumoniae? - ✔✔They
are part of a secretion system that helps in the uptake of DNA during transformation
competence.
