Operon Concept (Level : Moderate)
Comprehensive quiz on lac operon structure, regulation, and function in prokaryotic gene expression
Questions
What happens in lac operon when glucose is present?
- Cyclic AMP is high, the catabolite activator protein (CAP) binds to the activator binding site and transcription of lactose is turned on.
- Cyclic AMP is low, CAP does not bind to the activator binding site and transcription is turned off.
- Cyclic AMP is low, CAP binds to the activator binding site and transcription of lactose is turned on.
- Cyclic AMP is high, CAP does not bind to the activator binding site and transcription of lactose is turned on.
What happens in lac operon when both glucose and lactose are present in the cell?
- CAP binds to the activator binding site.
- RNA polymerase binds to the promoter.
- There is little or insufficient cyclic AMP.
- Lactose binds to the repressor and transcription takes place.
What is the function of lac repressor?
- It binds to the CAP site and prevents transcription.
- Lac repressor binds to the CAP site and facilitates transcription.
- Lac repressor binds to the operator and prevents transcription.
- Lac repressor binds to the operator and facilitates transcription.
In lac operon, RNA polymerase binds to
- operator
- promoter
- activator
- structural proteins
The lacY gene of lac operon codes for
- β-galactosidase
- lactose permease
- transacetylase
- RNA polymerase
Repressor proteins are encoded by
- promoter genes
- operator genes
- regulatory genes
- structural genes
Which of the following structural genes encodes for enzyme that is responsible for cleavage of lactose into glucose and galactose?
- LacY
- LacZ
- LacA
- LacL
Which of the following enzymes is not produced by E. coli during lactose metabolism?
- Lactose dehydrogenase
- Galactoside O-acetyltransferase
- Beta-galactosidase
- Lactose permease
An operon is a
- functioning unit of chromosome containing a cluster of DNA molecules under the control of a single promoter
- functioning unit of genomic DNA containing a cluster of genes under the control of a single promoter
- functioning unit of genomic DNA containing a cluster of genes under the control of a single operator
- functioning unit of chromosome containing a cluster of DNA molecules under the control of a single operator
Lac operon is an example of
- negative repressible operons
- negative inducible operons
- positive inducible operons
- positive repressible operons
Which of the following proteins is not regulated by the repressor in lac operon of E. coli?
- Beta-galactosidase
- Lactose permease
- Tryptophan
- Transacetylase
A polycistronic mRNA
- carries the information for more than one type of protein
- carries the information for a single type of protein
- contains codons of more than one cistron
- Both (1) and (3)
Which of the following statements is true?
- The lac repressor binds with lactose and transcription occurs when both glucose and lactose are present in the cell.
- When both glucose and lactose are absent, transcription occurs.
- In the absence of glucose, when lactose is present, it combines with the repressor, allowing RNA polymerase to carry on transcription.
- When glucose is present, cyclic AMP is high, CAP does not bind to the activator binding site and transcription of lactose is turned on.
The lac operator is located
- adjacent to activator
- partially within the promoter
- within the structural genes
- just before terminator
Who got the Nobel Prize in 1965 for the discovery of operon?
- Beadle and Tatum
- Temin and Baltimore
- Jacob and Monad
- John Otto