Regulasi Ekspresi Gen Prokariot

Summary

This script discusses gene expression control in prokaryotic organisms, focusing on operons. It explains structural genes, regulatory genes, and control sites, detailing how regulatory proteins like repressors and activators influence transcription. Examples include the lac operon, which is regulated by lactose, and the trp operon, controlled by tryptophan levels. The concept of catabolite repression and attenuation, which fine-tune gene expression, are also covered.

Takeaways

• 🧬 Prokaryotic gene expression is controlled by a group of structural genes and control sites known as an operon.
• 🔑 Regulatory genes and control sites are crucial for regulating the transcription rate of structural genes.
• 🔄 Regulatory proteins can either activate or repress the transcription process, with activators promoting transcription and repressors inhibiting it.
• 📉 Negative control involves repressor proteins that inhibit transcription, with two types: constitutive and repressible operons.
• 📈 Positive control involves activator proteins that stimulate transcription, with two types: inducible and repressible operons.
• 🍼 The lac operon in E. coli is a well-studied model for understanding gene regulation in prokaryotes, consisting of three structural genes and associated control sites.
• 🚫 Catabolite repression is a form of positive control where the presence of glucose represses the transcription of other sugar-metabolizing genes.
• 🔄 Attenuation is an additional level of control that affects the continuation of the transcription process beyond initiation.
• 📊 The trp operon is an example of a negatively repressible operon that controls the biosynthesis of the amino acid tryptophan.
• 🔋 Antisense RNA can regulate gene expression by binding to mRNA and inhibiting ribosome binding, as seen with the regulation of the UMP gene in E. coli.

Q & A

What is the role of the operator in prokaryotic gene expression?

The operator is a short sequence of nucleotides in DNA that controls the expression of structural genes. It is part of the regulatory region of an operon and is where RNA polymerase binds to initiate transcription.

What are the two main types of regulatory proteins involved in gene expression in prokaryotes?

The two main types of regulatory proteins are repressors and activators. Repressors inhibit transcription, while activators stimulate it.

How does the lac operon regulate the metabolism of lactose in E. coli?

The lac operon is composed of structural genes that code for enzymes involved in lactose metabolism. It is regulated by the presence of lactose, which can bind to the repressor protein, changing its conformation and allowing RNA polymerase to bind to the promoter and initiate transcription.

What is meant by the term 'catabolite repression' in the context of gene regulation?

Catabolite repression is a form of positive control where the presence of glucose represses the transcription of genes necessary for the metabolism of other sugars. This is because glucose is a preferred carbon source and requires less energy to metabolize.

What is the function of the CAP protein in E. coli?

The CAP protein, or cAMP receptor protein, binds to cAMP and helps in the regulation of gene expression in response to glucose levels. When glucose levels are high, CAP binds to DNA and stimulates transcription of genes involved in carbohydrate metabolism.

What is the role of the trp operon in the biosynthesis of tryptophan?

The trp operon controls the biosynthesis of tryptophan by regulating the transcription of genes involved in its synthesis. When tryptophan levels are high, it binds to the repressor protein, which then binds to the operator and inhibits transcription.

What is attenuation and how does it control gene expression?

Attenuation is a regulatory mechanism that controls gene expression at the level of transcription elongation. It involves the formation of secondary structures in the mRNA that can lead to premature termination of transcription.

How does the presence of tryptophan affect the trp operon?

When tryptophan levels are high, it binds to the repressor protein, activating it and allowing it to bind to the operator site, which inhibits transcription of the trp operon and thus the synthesis of tryptophan biosynthetic enzymes.

What is the role of the regulatory gene in an operon?

The regulatory gene produces RNA that can be transcribed into regulatory proteins, which help control the transcription of structural genes within an operon.

How does the lac operon respond to the presence of lactose?

In the presence of lactose, the lac operon is activated. Lactose binds to the repressor protein, changing its conformation and allowing RNA polymerase to bind to the promoter and initiate transcription of the lac operon.

What is the significance of the CRP binding site in the lac operon?

The CRP binding site is a regulatory site that interacts with the cAMP receptor protein (CRP). When bound to cAMP, CRP can stimulate the transcription of the lac operon by enhancing the binding of RNA polymerase to the promoter.