28 Questions
What happens when glucose levels are low in relation to cAMP levels and the lac genes?
CRP-cAMP forms and binds to the DNA
In the absence of lactose, why does transcription not occur in the lac operon?
The absence of allolactose
How does the binding of allolactose to the repressor affect transcription in the presence of lactose?
Prevents the repressor from binding to DNA
What is the main characteristic of an operon in bacteria?
A cluster of genes sharing a promoter and regulatory sequences
Which enzyme in the lac operon is responsible for the cleavage of lactose into glucose and galactose?
β-galactosidase (lacZ)
Which of the following proteins regulate transcription in an operon by either activating or repressing it?
Proteins binding to regulatory sequences
In the lac operon, what is the function of lactose permease (galactoside permease; lacY)?
Transports lactose into the cell
Which form of regulation is primarily involved in controlling the lac operon?
Negative regulation via a repressor
What is the main function of CRP-cAMP in the lac operon system?
Stimulating transcription
Under what condition does CRP-cAMP have its stimulatory effect on lac operon transcription?
Low glucose and high cAMP
What is the role of allolactose in the lac operon system?
Causing repressor dissociation from operator
In the absence of lactose and with high glucose levels, what is the impact on lac operon transcription?
No transcription due to repressor binding
What are the two requirements for the strongest induction of the lac operon?
[Glucose] must be low and cAMP must increase
What is a common characteristic of enhancers in bacteria?
Enhancers are often adjacent to weak promoters.
In positive regulation, what is the role of activators like CRP in the lac operon?
Activators stimulate transcription in the presence of a signal.
What is the outcome of repressor dissociation from DNA in negative regulation?
Transcription is stimulated.
How does effector binding alter the activity of activators or repressors?
Effector binding may increase or decrease activator or repressor affinity for DNA elements.
What occurs when a signal causes a repressor to dissociate from DNA?
Transcription is stimulated.
How does the Lac repressor help prevent RNA polymerase from binding to the promoter?
By binding primarily to the O1 operator adjacent to the promoter
What role does glucose play in the regulation of lactose-digesting genes in the Lac operon?
Turns off lactose genes when present
What is the primary function of the Lac repressor in the lac operon?
To prevent RNA polymerase from binding to the promoter
Which molecule mediates catabolite repression in the Lac operon?
cAMP and cAMP Receptor Protein (CRP)
What effect does binding of the Lac repressor to secondary operators (O2 or O3) have on transcription?
Reduces transcription but still occurs at a low rate
What is the outcome when CRP-cAMP is bound to DNA in the lac operon system?
Transcription is activated
Which molecule prevents the repressor from binding to DNA in the lac operon system?
Allolactose
What are the major groove characteristics that facilitate protein binding to DNA?
Exposes hydrogen bonding groups for alpha-helix binding
How do Gln/Asn amino acids contribute to DNA-binding specificity?
Form specific hydrogen bonds with Thymine-Adenine base pairs
Which condition leads to the absence of CRP binding in the lac operon system?
[cAMP] is low and glucose levels are high
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