Biochem Lecture 14a

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What happens when glucose levels are low in relation to cAMP levels and the lac genes?

CRP is bound to the DNA
CRP-cAMP forms and binds to the DNA (correct)
No transcription occurs because CRP is not bound
Activation of transcription of the lac genes at high levels

In the absence of lactose, why does transcription not occur in the lac operon?

Low cAMP levels prevent CRP binding
CRP is bound to the DNA
The absence of allolactose (correct)
No specific reason, transcription should occur

How does the binding of allolactose to the repressor affect transcription in the presence of lactose?

Facilitates binding of CRP to DNA
Enhances CRP-cAMP formation
Increases cAMP levels
Prevents the repressor from binding to DNA (correct)

What is the main characteristic of an operon in bacteria?

A cluster of genes sharing a promoter and regulatory sequences (B) Signup and view all the answers

Which enzyme in the lac operon is responsible for the cleavage of lactose into glucose and galactose?

β-galactosidase (lacZ) (D) Signup and view all the answers

Which of the following proteins regulate transcription in an operon by either activating or repressing it?

Proteins binding to regulatory sequences (A) Signup and view all the answers

In the lac operon, what is the function of lactose permease (galactoside permease; lacY)?

Transports lactose into the cell (B) Signup and view all the answers

Which form of regulation is primarily involved in controlling the lac operon?

Negative regulation via a repressor (C) Signup and view all the answers

What is the main function of CRP-cAMP in the lac operon system?

Stimulating transcription (D) Signup and view all the answers

Under what condition does CRP-cAMP have its stimulatory effect on lac operon transcription?

Low glucose and high cAMP (D) Signup and view all the answers

What is the role of allolactose in the lac operon system?

Causing repressor dissociation from operator (C) Signup and view all the answers

In the absence of lactose and with high glucose levels, what is the impact on lac operon transcription?

No transcription due to repressor binding (D) Signup and view all the answers

What are the two requirements for the strongest induction of the lac operon?

[Glucose] must be low and cAMP must increase (B) Signup and view all the answers

What is a common characteristic of enhancers in bacteria?

Enhancers are often adjacent to weak promoters. (B) Signup and view all the answers

In positive regulation, what is the role of activators like CRP in the lac operon?

Activators stimulate transcription in the presence of a signal. (C) Signup and view all the answers

What is the outcome of repressor dissociation from DNA in negative regulation?

Transcription is stimulated. (A) Signup and view all the answers

How does effector binding alter the activity of activators or repressors?

Effector binding may increase or decrease activator or repressor affinity for DNA elements. (A) Signup and view all the answers

What occurs when a signal causes a repressor to dissociate from DNA?

Transcription is stimulated. (D) Signup and view all the answers

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 (C) Signup and view all the answers

What role does glucose play in the regulation of lactose-digesting genes in the Lac operon?

Turns off lactose genes when present (D) Signup and view all the answers

What is the primary function of the Lac repressor in the lac operon?

To prevent RNA polymerase from binding to the promoter (B) Signup and view all the answers

Which molecule mediates catabolite repression in the Lac operon?

cAMP and cAMP Receptor Protein (CRP) (B) Signup and view all the answers

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 (B) Signup and view all the answers

What is the outcome when CRP-cAMP is bound to DNA in the lac operon system?

Transcription is activated (B) Signup and view all the answers

Which molecule prevents the repressor from binding to DNA in the lac operon system?

Allolactose (D) Signup and view all the answers

What are the major groove characteristics that facilitate protein binding to DNA?

Exposes hydrogen bonding groups for alpha-helix binding (D) Signup and view all the answers

How do Gln/Asn amino acids contribute to DNA-binding specificity?

Form specific hydrogen bonds with Thymine-Adenine base pairs (A) Signup and view all the answers

Which condition leads to the absence of CRP binding in the lac operon system?

[cAMP] is low and glucose levels are high (C) Signup and view all the answers