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List the three components of an operon, and explain the role of each one.
How does a repressor protein work?
What are regulatory genes?
Distinguish between inducible and repressible operons, and describe one example of each type.
Label this sketch of the lac operon with the following terms: (Know the function of each structure).
Operon, genes, RNA polymerase, mRNA, Repressor, Operator Repressor Regulatory gene Induce
Compare and contrast the lac operon and the trp operon. (Remember that compare means “to tell how they are similar,” and contrast means “to tell how they are different.”)
What happens when there is a mutation in the repressor? Operator? Lac I gene?
Explain why CAP binding and stimulation of gene expression is positive regulation.
Describe the relationship between glucose supply, cAMP, and CAP.
Gene expression can be regulated by modifications of the chromatin. Distinguish between heterochromatin and euchromatin as to their structure and activity.
What occurs in histone acetylation? How does it affect gene expression?
What is DNA methylation? What role may it play in gene expression?
Posttranscriptional control includes regulation of mRNA degradation. Explain how this affects translation.
Answered Same Day Sep 24, 2023


Dr Insiyah R. answered on Sep 25 2023
28 Votes
Ans: 1
An operon is a functional unit of DNA containing several genes under the control of a single promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm or undergo splicing to create monocistronic mRNAs that are translated separately. The operon is a common feature in prokaryotic organisms and serves to regulate gene expression. The three main components of an operon are:
1. Promoter:- The promoter is a DNA sequence located upstream of the operon that serves as the binding site for RNA polymerase. RNA polymerase binds to the promoter to initiate transcription of the operon.
Role: The promoter controls the rate at which transcription is initiated, effectively regulating the expression of the genes within the operon.
2. Operator:- The operator is a specific DNA sequence located between the promoter and the operon's genes. It acts as a regulatory sequence that a repressor protein can bind.
Role: When the repressor protein binds to the operator, it prevents RNA polymerase from transcribing the genes in the operon, thereby regulating gene expression.
3. Structural Genes:- Structural genes are the actual genes within the operon that code for proteins. These genes are transcribed together into a single mRNA molecule.
Role: The structural genes encode the proteins necessary for the organism's survival or for ca
ying out specific cellular functions.
In addition to these components, some operons also contain a regulator gene, which codes for the repressor protein that can bind to the operator and inhibit transcription. The presence or absence of certain molecules, such as nutrients or metabolites, can influence whether the repressor protein binds to the operator, thereby acting as a mechanism for environmental response and regulation of gene expression.
Ans 2:
A repressor protein is a type of regulatory protein that plays a crucial role in controlling gene expression in both prokaryotic and eukaryotic organisms. In the context of a prokaryotic operon, the repressor protein functions to inhibit transcription by binding to the operator sequence. Here’s a detailed explanation of how a repressor protein works in a prokaryotic operon:
1. Binding to Operator:-
The repressor protein can bind to the operator sequence of the operon. When the repressor is bound to the operator, it physically blocks the advancement of RNA polymerase along the DNA strand, preventing it from transcribing the structural genes downstream of the operator.
2. Response to Inducers or Corepressors:-
The activity of the repressor protein is often modulated by small molecules called inducers or corepressors.
An inducer is a molecule that binds to the repressor protein and alters its conformation in a way that it can no longer bind to the operator. This alleviates the block on RNA polymerase, allowing transcription to proceed.
A corepressor is a molecule that binds to the repressor protein and enables it to bind to the operator, thereby inhibiting transcription.
3. Lac Operon as an Example:- A well-known example of a repressor protein at work is in the lac operon of E. coli. The lac operon contains genes necessary for the metabolism of lactose.
The lac repressor is active in its native form and binds to the operator to inhibit transcription when lactose is absent.
When lactose is present, it acts as an inducer by binding to the lac repressor and causing a conformational change, rendering it unable to bind to the operator. As a result, the structural genes of the lac operon are transcribed, and the enzymes necessary for lactose metabolism are produced.
Ans 3:
Regulatory genes are a type of gene that produces products, usually proteins, that control or regulate the expression of other genes. These genes are critical for the proper development, growth, and functioning of organisms, as they help to ensure that the right genes are expressed at the right time and in the right cells. Regulatory genes play a central role in responding to environmental changes and maintaining homeostasis within the cell.
Here are the main types of products that regulatory genes typically encode and their functions:
1. Transcription Factors:- Transcription factors are proteins that bind to specific DNA sequences, usually in the promoter region of target genes, to regulate transcription. They can either activate or repress the expression of genes by influencing the binding of RNA polymerase or by recruiting other proteins involved in transcriptional regulation.
2. Repressors:- Repressors are a type of transcription factor that inhibits the transcription of a gene or a set of genes. They often work by binding to the operator region of an operon or other regulatory sequences in the DNA, thereby blocking the access of RNA polymerase to the gene(s).
3. Activators:- Activators are another type of transcription factor that promotes the transcription of a gene or set of genes. They typically work by binding to enhancer regions or promoter sequences in the DNA and facilitating the binding of RNA polymerase to the gene(s).
4. Small RNAs:- Some regulatory genes encode small RNAs, such as microRNAs (miRNAs) and small interfering RNAs (siRNAs), which play a role in post-transcriptional regulation. These small RNAs can bind to messenger RNAs (mRNAs) and either inhibit their translation or lead to their degradation.
5. Hormones:- Some regulatory genes encode hormones, which are signalling molecules that can travel throughout the organism to influence the activity of other cells. Hormones can regulate gene expression by binding to hormone receptors, which can then...

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