14 Questions
What does a regulator gene encode?
Products that regulate the expression of other genes
What is required to turn on the expression of structural genes in positive control mechanisms?
Activator
What happens in negative regulation - I when a molecular signal is present?
Dissociation of the regulatory protein from DNA
What is the function of the repressor protein in the operon model?
Binding to the operator
Which type of regulation involves binding of a regulatory protein to DNA to inhibit transcription?
Negative regulation - II
What happens in positive regulation - I when a molecular signal is present?
What happens in positive regulation - II when a molecular signal is present?
Binding of regulatory protein to DNA
Which describes the function of the promoter in the operon model?
It is the site of transcription initiation for the structural gene(s)
Which molecular signal causes the dissociation of the regulatory protein from DNA in negative regulation - I?
Signal molecule
What occurs in negative regulation when a repressor is bound to DNA?
Transcription is inhibited
Which of the following is NOT part of the operon model?
Repressor protein deactivation site
What is the role of the activator binding site in the operon model?
It binds activator proteins to facilitate transcription
In positive regulation - I, what is the effect of a molecular signal causing dissociation of a regulatory protein from DNA?
Activation of transcription
What defines an operon?
A cluster of related genes turned off/on together
Study Notes
Control Mechanisms
- Regulator genes encode products that regulate the expression of other genes.
- Positive control mechanisms require the product of the regulator gene (activator) to turn on the expression of structural genes.
- Negative control mechanisms require the product of the regulator gene (repressor) to shut off the expression of structural genes.
- These mechanisms are altered by binding to an effector (signal) molecule.
Negative Regulation
- A bound repressor inhibits transcription by binding to the operator.
- Molecular signal causes binding of regulatory protein to DNA.
- Signal molecule dissociates regulatory protein from DNA.
Positive Regulation
- A bound activator facilitates transcription by binding to a specific site.
- RNA polymerase is involved in transcription.
- Molecular signal causes dissociation of regulatory protein from DNA.
Operons
- Operons are coordinately regulated units of gene expression or clusters of related genes turned off/on together.
- An operon consists of:
- Activator and repressor binding sites
- Promoter where sigma factor binds
- One or more genes whose expression is controlled by the operon
- Genes in an operon are transcribed as a single polycistronic mRNA that is translated into multiple proteins.
- The promoter is the site of transcription initiation for the structural gene(s).
- The repressor protein binds to the operator, regulated by the presence or absence of an effector molecule, to regulate transcription of the structural gene(s).
This quiz covers the basics of positive and negative control mechanisms in gene expression. It explains how regulator genes and their products interact with effector molecules to regulate structural genes.
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