module 7 lec 9 Flashcards
What is the operon theory in gene regulation?
The operon theory suggests that a single signal can regulate the expression of several genes that are clustered together and involved in the same process.
What is an operon?
An operon is a cluster of genes that are transcribed together as a single mRNA in bacteria, typically under the control of a single promoter.
What does polycistronic mean?
Polycistronic refers to an mRNA transcript that contains the coding sequences for multiple genes, which are usually part of an operon.
How are bacterial genes typically arranged for coordinated regulation?
Bacterial genes involved in the same process are often clustered together in an operon and transcribed as a single mRNA.
Why is the operon model important in understanding gene regulation?
The operon model explains how bacteria can regulate multiple genes simultaneously with a single regulatory mechanism, allowing efficient responses to environmental changes.
What happens if the inducer binding domain of the repressor is mutated?
If the inducer binding domain is mutated, it leads to constant repression of the gene, as the repressor cannot be deactivated by the inducer.
What is the effect of a mutation in the DNA binding domain of the repressor?
A mutation in the DNA binding domain causes the repressor to fail to bind to the operator, resulting in constant expression of the gene.
How does a mutation in the operator DNA sequence affect gene expression?
A mutation in the operator sequence prevents the repressor from binding, leading to constant expression of the gene.
How can mutations in the lac operon lead to constant repression?
Mutations in the inducer binding domain of the repressor prevent the repressor from being inactivated, causing constant repression of the operon.
How can mutations in the lac operon lead to constant expression?
Mutations in the DNA binding domain of the repressor or the operator sequence cause the gene to be constantly expressed, as the repressor can no longer bind properly.
What is the difference between cis and trans acting elements?
Cis acting elements affect only genes on the same DNA molecule, while trans acting elements can diffuse and affect genes on any DNA molecule in the cell.
How can we distinguish between a mutant repressor and a mutant operator?
Both can cause constitutive expression of the lac operon, but mutant repressors are trans acting (can affect any operon), while mutant operators are cis acting (only affect the lac operon on the same DNA molecule).
What are trans acting elements?
rans acting elements are factors (like mutant repressors) that can diffuse through the cytoplasm and regulate genes on any DNA molecule in the cell.
What are cis acting elements?
Cis acting elements are DNA sequences (like the operator) that influence gene expression only on the same DNA molecule they are located on.
Can cis acting mutations affect distant genes?
No, cis acting mutations only affect genes on the same DNA molecule. They cannot influence distant gene
What are the main components of the lac operon?
lacZ, lacY, lacA genes, promoter site, cis acting operator site, trans acting repressor (encoded by lacI), and inducer.
What does the lacZ, lacY, and lacA genes do?
They split lactose into glucose and galactose.
What is the function of the promoter in the lac operon
The promoter is where RNA polymerase binds to begin transcription.
What is the role of the cis acting operator site?
It’s where the repressor binds to block transcription.
What does the trans acting repressor do?
The repressor (encoded by lacI) binds to the operator to prevent transcription.
What is the role of the inducer in the lac operon?
The inducer binds to the repressor, preventing it from binding to the operator, thus allowing gene expression.
What happens when glucose is low in the cell?
cAMP levels rise and bind to CRP (cAMP receptor protein).
What does the CRP-cAMP complex do?
It binds to the lac promoter and enhances RNA polymerase activity.
What is the role of CRP in the lac operon
CRP activates transcription of the lac operon when glucose is low by helping RNA polymerase bind to the promoter.
How does cAMP influence gene expression in a catabolic operon?
cAMP binds to CRP, which then binds to the promoter, enhancing transcription when glucose is low.
What do negative regulators do in RNA polymerase regulation?
Negative regulators (e.g., lac repressor) block RNA polymerase’s DNA-binding sites, preventing transcription.
What is the role of positive regulators in RNA polymerase activity?
Positive regulators establish contact with RNA polymerase, enhancing its ability to initiate transcription.
How do negative regulators affect transcription
They inhibit transcription by preventing RNA polymerase from binding to DNA.
How do positive regulators affect transcription?
They promote transcription by helping RNA polymerase bind and initiate transcription more effectively.
What do DNA binding proteins usually consist of?
They usually consist of two or more subunits.
How do DNA binding proteins interact with DNA?
Each alpha helix in the protein makes contact with DNA bases via amino acid side chains
How do DNA binding proteins enhance interaction with DNA?
By forming multiple contacts with the promoter DNA, they increase stability of the DNA-protein interaction.
What is the role of amino acid side chains in DNA binding proteins?
They make contact with DNA bases, allowing the protein to bind to the DNA more effectively.
What are some conserved motifs found in DNA binding proteins?
Helix-turn-helix (HTH) is one common motif.
What does the helix-turn-helix (HTH) motif consist of?
It consists of two α-helical regions separated by a turn in the protein structure.
How does the helix-turn-helix motif interact with DNA?
The motif fits into the major groove of DNA, allowing binding
Which types of proteins typically have a helix-turn-helix motif?
Most repressor proteins have the helix-turn-helix motif.
