Regulasi Ekspresi Gen Prokariot

Ruth Chrisnasari

9 Sept 202018:52

Summary

TLDRThis 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.

Outlines

00:00

🧬 Gene Expression Control in Prokaryotes

This paragraph discusses the mechanisms of gene expression control in prokaryotic organisms. It introduces the concept of the operon, which includes structural genes and regulatory sites that control the rate of transcription. The paragraph explains how regulatory genes, which consist of promoters and can be transcribed into mRNA and then translated into regulatory proteins, help control the transcription of structural genes. These proteins can either activate or repress transcription. The paragraph also covers the two types of transcription control in prokaryotes: negative control and positive control, with examples of how these controls work in different operons.

05:00

🔬 The lac Operon: A Model for Gene Regulation

The second paragraph delves into the lac operon in E. coli as a model for gene regulation in prokaryotes. It describes the structure of the lac operon, which includes three structural genes and several control sites. The paragraph explains how the lac operon is regulated by the presence of lactose and how the regulatory proteins interact with the operator to either allow or inhibit transcription. It also discusses the role of the lac repressor and how it can be converted from an inactive to an active state by binding with lactose, thus controlling the transcription of the lac operon.

10:03

🌐 Catabolite Repression and the Trp Operon

This section explores the concept of catabolite repression, a form of positive control in gene regulation, which is influenced by the presence of glucose. It explains how the presence of glucose can repress the transcription of genes involved in metabolizing other sugars, such as the trp operon, which controls the biosynthesis of the amino acid tryptophan. The paragraph also discusses the role of the trp repressor and how it can be converted from an inactive to an active state by binding with tryptophan, thereby inhibiting the transcription of the trp operon.

15:04

🔄 Attenuation: A Post-Initiation Control Mechanism

The final paragraph discusses attenuation, a post-initiation control mechanism that affects the continuation of the transcription process beyond initiation. It provides an example of how attenuation occurs in the trp operon, with a focus on the leader region and the role of ribosomes in controlling transcription. The paragraph explains how the presence of tryptophan can influence the formation of secondary structures in the mRNA, which in turn can lead to premature termination of transcription. It also touches on the control of translation by antisense RNA and provides an example of how this mechanism regulates gene expression in E. coli.

Mindmap

Keywords

💡Prokaryotic

Prokaryotic refers to organisms whose cells lack a nucleus and other membrane-bound organelles. In the context of the video, prokaryotes are the focus for discussing gene expression control mechanisms. The video mentions prokaryotes to explain the simpler yet effective ways these organisms regulate gene expression, such as through operons.

💡Gene Expression

Gene expression is the process by which the information from a gene is used to synthesize functional gene products, typically proteins. The video discusses how gene expression is controlled in prokaryotes, which is central to understanding how these organisms adapt and respond to their environment.

💡Operon

An operon is a unit of DNA that includes a set of genes under the control of a single regulatory region. The video explains that operons are a key feature in prokaryotic gene regulation, allowing coordinated expression of multiple genes involved in a particular metabolic pathway.

💡Regulatory Genes

Regulatory genes are segments of DNA that encode for proteins that control the transcription of other genes. The video highlights the role of regulatory genes in controlling the rate of transcription of structural genes within an operon, thus playing a crucial role in gene expression.

💡Promoter

A promoter is a DNA sequence that signals the start of transcription. The video mentions promoters as part of the regulatory elements that help control the transcription of genes within an operon.

💡Transcription

Transcription is the process of creating an RNA copy of a gene's DNA sequence. The video discusses how the rate of transcription is regulated by various mechanisms in prokaryotes, such as through the binding of regulatory proteins to control sites.

💡Regulatory Proteins

Regulatory proteins are proteins that bind to DNA and influence gene expression. The video explains that these proteins can act as either activators or repressors, controlling whether transcription occurs by binding to control sites near the genes they regulate.

💡Activator

An activator is a type of regulatory protein that binds to specific DNA sequences and increases the rate of transcription of a gene or operon. The video describes activators as proteins that help initiate transcription when bound to control sites.

💡Repressor

A repressor is a regulatory protein that inhibits transcription by binding to operator sites. The video uses repressors to illustrate how the absence of certain molecules (like a repressor) can allow transcription to proceed.

💡Catabolite Repression

Catabolite repression is a mechanism where the presence of a preferred carbon source (like glucose) represses the expression of enzymes for utilizing other carbon sources. The video discusses this concept in the context of the lac operon in E. coli, explaining how the presence of glucose can repress the expression of genes needed for metabolizing lactose.

💡Lac Operon

The lac operon is a well-studied example of an operon that controls the enzymes necessary for lactose metabolism in E. coli. The video uses the lac operon to explain how negative regulation works, with the presence of lactose inducing the expression of the operon.

💡Attenuation

Attenuation is a regulatory mechanism that controls gene expression at the level of transcription termination. The video describes how attenuation works in the trp operon, where the formation of secondary mRNA structures can lead to premature termination of transcription.

Highlights

Pengontrol ekspresi gen pada organisme prokariotik melalui struktural gen dan kontroling site yang dikenal sebagai operon.

Struktural gen adalah sekwen nukleotida dari DNA yang digunakan sebagai template untuk sintesis RNA.

Regulatory operon terdiri dari regulatory gen dan kontroling site yang membantu meregulasi transkripsi sukral gen.

Regulator gen memiliki promotor dan ditranskripsikan menjadi mRNA pendek yang kemudian ditranslasikan menjadi protein kecil yang dikenal sebagai regulatory proteins.

Simulator protein membantu ekspresi sukral gen dengan cara terikat pada kontroling site, dapat mengaktivasi atau menghambat transkripsi.

Regulatory protein yang menstimulasi transkripsi gen disebut activator, sementara yang menghambat disebut represor.

Terdapat dua tipe pengontrolan transkripsi yaitu negatif kontrol dan positif kontrol.

Negatif kontrol melibatkan regulatory protein sebagai represor yang menghambat transkripsi.

Positif kontrol melibatkan regulatory protein sebagai activator yang menstimulasi terjadinya transkripsi.

Operon polisistronik terdiri dari beberapa situr algen atau systron dan kontroling site.

Regulon adalah sekelompok operon yang dikontrol oleh satu regulatory protein.

Laktosa operon pada E. coli merupakan model yang baik untuk menjelaskan regulasi gen pada prokariotik.

Katabolit repression merupakan kontrol positif terhadap keberadaan glukosa yang melibatkan peran di merek protein.

Triptofan operon atau Trp operon mengontrol biosintesis asam amino triptofan.

Transkripsi dimulai pada start site, tetapi terminasi terjadi secara prematur, yaitu sebelum RNA polimerase mencapai struktural gen.

Attenuation adalah kontrol lebih lanjut dari proses transkripsi yang mempengaruhi kelanjutan proses transkripsi dari inisiasi.

Regulasi gen UMP pada E. coli menunjukkan bagaimana antisense RNA dapat menghambat pengikatan ribosom dan mengontrol translasi.