Gene Expression Control and Enzyme Regulation
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Questions and Answers

What is the primary function of the repressor protein in the Trp operon?

  • To degrade mRNA
  • To enhance transcription
  • To block RNA polymerase (correct)
  • To activate RNA polymerase

What is the primary function of tumour suppressor genes?

  • To enhance signal transduction
  • To facilitate oncogenesis
  • To promote cell division
  • To inhibit cell division (correct)

In the Lac operon, what is the role of allolactose?

  • It serves as an inducer (correct)
  • It competes with cAMP
  • It acts as a corepressor
  • It binds to RNA polymerase

How do Ras point mutations affect cell signaling?

<p>They switch Ras ON without control. (B)</p> Signup and view all the answers

What type of regulation occurs when a corepressor binds to a transcription factor?

<p>Negative regulation (A)</p> Signup and view all the answers

What role does p53 play in the cell cycle?

<p>It acts as a checkpoint to halt the cell cycle when DNA is damaged. (C)</p> Signup and view all the answers

In the context of the Lac operon, what must be true for the CAP protein to bind to the promoter?

<p>Cyclic AMP must be present (D)</p> Signup and view all the answers

What is the outcome when both a corepressor and an inducer are present in an operon?

<p>Repression of gene expression (D)</p> Signup and view all the answers

What is the consequence of p53 mutations?

<p>They allow cells to continue dividing despite DNA damage. (B)</p> Signup and view all the answers

How do transcription factors affect RNA polymerase activity?

<p>They can either activate or inhibit transcription (B)</p> Signup and view all the answers

Which gene is classified as a proto-oncogene?

<p>Ras (C)</p> Signup and view all the answers

What is required before cell cycle control is lost in cancer development?

<p>Mutations in several genes (D)</p> Signup and view all the answers

What does the lexical term 'operon' specifically define in bacteria?

<p>A cluster of related genes regulated by a single promoter (D)</p> Signup and view all the answers

What technology can be used to track mutations associated with cancer?

<p>Genomic technology (C)</p> Signup and view all the answers

Which of the following correctly describes a positive gene regulation mechanism?

<p>The presence of an inducer enhances transcription (D)</p> Signup and view all the answers

Which of the following statements is true regarding cancer and cell cycle control?

<p>Misregulation of cell cycle control genes contributes to cancer. (C)</p> Signup and view all the answers

Which best describes the relationship between negative and positive regulation in an operon system?

<p>They can compete for control over gene expression (D)</p> Signup and view all the answers

In eukaryotic gene regulation, which factor is crucial for activating transcription?

<p>Enhancers and transcription factors (B)</p> Signup and view all the answers

What regulates the transcription of genes in prokaryotes?

<p>Operons, repressors, and activators (A)</p> Signup and view all the answers

What is necessary for a complete understanding of cancer-related mutations?

<p>Comprehensive knowledge of complex molecular biology (C)</p> Signup and view all the answers

What effect does chromatin packaging have on gene regulation?

<p>Tightly packaged chromatin is inaccessible to transcription factors. (B)</p> Signup and view all the answers

How do acetyl groups influence chromatin structure?

<p>They loosen histone proteins enhancing accessibility. (A)</p> Signup and view all the answers

What is the role of enhancers in gene transcription?

<p>They are distant sites that increase transcription factor activity. (A)</p> Signup and view all the answers

What defines an oncogene?

<p>A mutated gene that promotes cancer. (B)</p> Signup and view all the answers

Which statement best describes proto-oncogenes?

<p>They regulate cell division when needed. (D)</p> Signup and view all the answers

What is the primary characteristic of tumor suppressor genes?

<p>They inhibit cell division and prevent tumor formation. (C)</p> Signup and view all the answers

What contributes to the cooperative effects among transcription factors?

<p>The ability of DNA to loop and bring distant sites closer. (B)</p> Signup and view all the answers

What happens when proto-oncogenes mutate?

<p>They lose their ability to regulate cell division. (A)</p> Signup and view all the answers

How do transcription factors interact with promoters?

<p>They assist RNA polymerase in initiating transcription. (A)</p> Signup and view all the answers

Which statement describes the expression of proto-oncogenes?

<p>They are only expressed in response to cellular signaling. (C)</p> Signup and view all the answers

What is the main purpose of a promoter in an operon?

<p>To serve as a binding site for RNA polymerase (A)</p> Signup and view all the answers

In the Trp operon, the Trp repressor protein requires which molecule to bind to the operator?

<p>Tryptophan (D)</p> Signup and view all the answers

What role does cyclic AMP (cAMP) play in the regulation of the Lac operon?

<p>It acts as a coactivator for the CAP protein (A)</p> Signup and view all the answers

What happens when the Lac repressor is bound to the operator?

<p>Transcription is blocked (D)</p> Signup and view all the answers

Which of the following best describes negative gene regulation?

<p>It relies on the presence of corepressors to inhibit transcription (D)</p> Signup and view all the answers

In the context of gene regulation, what is an example of a coactivator?

<p>cAMP (A)</p> Signup and view all the answers

Which statement accurately describes a transcription factor's role in positive regulation?

<p>It activates RNA polymerase when bound to an operator (C)</p> Signup and view all the answers

How does the presence of both a corepressor and an inducer affect gene regulation in an operon?

<p>It causes competition between regulatory proteins (D)</p> Signup and view all the answers

What defines the role of a coactivator in the expression of the Lac operon?

<p>It helps stabilize the binding of transcription factors to the promoter (B)</p> Signup and view all the answers

What is the competitive interaction between the Lac repressor and the CAP protein dictated by?

<p>The availability of lactose (B), The presence of cAMP (C)</p> Signup and view all the answers

What role do tumour suppressor genes primarily serve in cell regulation?

<p>They inhibit unnecessary cell division. (A)</p> Signup and view all the answers

What is a consequence of Ras activating mutations in cell signaling?

<p>Signal transduction remains permanently ON. (D)</p> Signup and view all the answers

Which gene is commonly referred to as the 'guardian of the genome'?

<p>p53 (D)</p> Signup and view all the answers

What is a primary effect of p53 mutations on the cell cycle?

<p>p53 accumulates more mutations in the cell. (C)</p> Signup and view all the answers

What is required for the initiation of oncogenesis due to mutations?

<p>Simultaneous mutations in several genes. (D)</p> Signup and view all the answers

Which statement accurately describes the role of genomic technology in cancer diagnosis?

<p>It tracks changes related to cancer development. (D)</p> Signup and view all the answers

How do mutations in tumour suppressor genes affect cell division?

<p>They lead to unregulated cell division. (C)</p> Signup and view all the answers

What complexity is involved in understanding cancer mechanisms?

<p>Understanding requires knowledge of complex molecular biology. (B)</p> Signup and view all the answers

What aspect of eukaryotic gene regulation is distinct from prokaryotic regulation?

<p>Eukaryotic regulation includes multiple levels of control. (A)</p> Signup and view all the answers

What role do enhancers play in gene regulation?

<p>They enable coordinate regulation of gene expression. (D)</p> Signup and view all the answers

How does chromatin packaging influence gene accessibility?

<p>Loose packaging allows transcription factors and RNA polymerase to access genes. (D)</p> Signup and view all the answers

What mechanism is proposed for switching genes on or off through histone modification?

<p>Acetylation of histones to promote a loosely packed structure. (D)</p> Signup and view all the answers

Which of the following correctly describes the role of enhancers in gene expression?

<p>Enhancers can be located far from the gene they regulate, yet still enhance transcription. (B)</p> Signup and view all the answers

What is a characteristic of proto-oncogenes in relation to cell growth?

<p>They stimulate cell growth and division under normal circumstances. (D)</p> Signup and view all the answers

What happens to proto-oncogenes when they undergo mutations?

<p>They lose their regulatory control, potentially leading to oncogenesis. (D)</p> Signup and view all the answers

How do transcription factors interact with promoters and enhancers?

<p>Transcription factors require enhancer binding to effectively initiate transcription at promoters. (D)</p> Signup and view all the answers

What is the role of cooperative effects among transcription factors?

<p>To enable distant regulatory sites to interact and enhance transcription. (B)</p> Signup and view all the answers

What are oncogenes primarily responsible for?

<p>Promoting cancer when mutated by stimulating excessive cell division. (A)</p> Signup and view all the answers

Which effect does chromatin packaging have on gene activation and repression?

<p>Tightly packed chromatin is associated with gene repression. (A)</p> Signup and view all the answers

What best describes the switching of genes using activator combinations?

<p>Activator combinations enable complex regulation across different cell types. (B)</p> Signup and view all the answers

Flashcards

Operon

A cluster of genes in bacteria that are regulated together by a single promoter.

Negative Gene Regulation

A type of gene regulation where a transcription factor (TF) blocks RNA polymerase from transcribing genes by binding to the operator sequence.

Repressor Protein

A protein that binds to the operator sequence and prevents RNA polymerase from transcribing genes.

Corepressor

A molecule that binds to a repressor protein, allowing the repressor to bind to the operator and block transcription.

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Inducer

A molecule that binds to a repressor protein, causing the repressor to release from the operator and allowing transcription to start.

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Positive Gene Regulation

A type of gene regulation where a transcription factor (TF) binds to the operator and activates RNA polymerase, promoting transcription.

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Activator Protein

A protein that binds to the operator and activates RNA polymerase to transcribe genes.

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Coactivator

A molecule that binds to an activator protein, allowing the activator to bind to the operator and activate transcription.

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Lac Operon

A cluster of genes in bacteria that are regulated by a single promoter and are involved in the breakdown of lactose.

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Trp Operon

A cluster of genes in bacteria that are regulated by a single promoter and are involved in the synthesis of tryptophan.

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Tumour Suppressor Genes

Genes that normally prevent uncontrolled cell division by inhibiting cell cycle progression.

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Proto-oncogene

A gene that has the potential to become an oncogene (cancer-causing gene) when mutated.

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Ras Protein

A proto-oncogene that acts in signal transduction pathways, helping activate the cell cycle.

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Ras Point Mutation

A specific mutation in the Ras gene that causes it to become permanently active, leading to uncontrolled cell division.

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p53 Tumor Suppressor

A gene that acts as a 'gatekeeper' of the cell cycle, halting cell division when DNA is damaged.

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p53 Point Mutation

A mutation in the p53 gene that inactivates its ability to stop the cell cycle when DNA is damaged.

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Multi-step Mutation

The development of cancer often requires multiple mutations in different genes, ultimately leading to uncontrolled cell growth.

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Genomic Technology in Cancer

The use of technology to analyze the entire genome of a cell or tumor, revealing the mutations involved in cancer development.

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Inheriting Cancer Mutations

Mutations in some genes involved in cancer can be inherited from parents, increasing the risk of developing cancer.

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Cancer Misregulation of Cell Cycle

Cancer arises from the misregulation of cell cycle control genes, causing cells to divide uncontrollably.

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Chromatin Packaging & Accessibility

The way DNA is packaged in chromatin affects the access of transcription factors and RNA polymerase. Loosely packaged DNA is accessible, tightly packaged DNA is inaccessible.

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Histone Acetylation

Adding acetyl groups to histone proteins in the nucleosome loosens chromatin packaging, making DNA more accessible for transcription.

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Transcription Factors (TFs)

Proteins that bind to specific DNA sequences and regulate the initiation of transcription.

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Promoter Region

DNA sequence immediately upstream of a gene where RNA polymerase binds to initiate transcription.

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Enhancer Regions

DNA sequences distant from the promoter that can bind activator proteins to boost transcription.

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Cooperative Transcription

Multiple transcription factors can work together to regulate gene expression. Activators and TFs can bind to different sites and interact to fine-tune gene activation.

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Gene Switching by Activator Combinations

Different combinations of activator proteins can activate or repress different genes, enabling precise control of gene expression in different cell types.

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Oncogenes

Mutated versions of proto-oncogenes that contribute to cancer development.

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Tumour Suppressors

Genes that normally inhibit cell growth and division. Mutations in tumour suppressors can cause cancer by removing the brakes on cell growth.

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Chromatin Packaging

The way DNA is organized and packed within the nucleus, influencing how accessible genes are to transcription.

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Accessible DNA

DNA that is loosely packaged, allowing transcription factors and RNA polymerase to bind and initiate transcription.

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Inaccessible DNA

DNA that is tightly packed, making it difficult for transcription factors and RNA polymerase to bind and initiate transcription.

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Promoter

DNA sequence located near the beginning of a gene, where RNA polymerase binds to initiate transcription.

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Enhancers

DNA sequences that can be located far from a gene, but still bind activator proteins to boost transcription.

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Ras

A proto-oncogene involved in signal transduction. It helps switch on the cell cycle when signals come from outside the cell.

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p53

A tumor suppressor gene that acts as a guardian of the genome. It checks for DNA damage and stops the cell cycle if necessary, preventing mutations from accumulating.

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Study Notes

Gene Expression Control

  • Gene expression is controlled at multiple levels
  • Prokaryotic gene regulation primarily uses operons
  • Operons are groups of related genes regulated by a single promoter
  • Repressors and activators control operon activity
  • Eukaryotic gene regulation involves multiple levels of control
  • Chromatin packaging affects accessibility of DNA
  • Transcription factors regulate transcription initiation
  • Transcription factors bind to specific DNA sequences
  • Multiple binding sites on DNA allowing transcription factors to interact at distant points
  • Combined effects of multiple factors affect initiation rate and efficiency in a complex fashion
  • Cooperative effects occur when distant sites interact to influence overall transcription

Enzyme Regulation

  • Enzyme activity can be regulated through feedback inhibition
  • Enzymes can also be regulated by controlling their production through controlling gene expression
  • Feedback inhibition involves the product of a pathway inhibiting an enzyme earlier in the pathway

Transcription Regulation (Case Studies)

  • Trp Operon (Negative):

    • Regulated by a repressor protein
    • Corepressor molecule (e.g. tryptophan) activates the repressor
    • When tryptophan is present, the repressor binds to the operator, blocking RNA polymerase and halting transcription
    • When tryptophan is absent, the repressor is inactive, allowing transcription to proceed

  • Lac Operon (Negative):

    • Controlled by a repressor protein
    • Inducer molecule (e.g. allolactose) inhibits repressor activity
    • When lactose is absent, the repressor binds to the operator, preventing RNA polymerase from transcribing the operon
    • When lactose is present, allolactose binds to the repressor causing it to detach from the operator, allowing transcription

  • Lac Operon (Positive):

    • Regulated by an activator protein (e.g. CAP protein)
    • Coactivator molecule (e.g. cyclic AMP) enhances activator activity
    • When cAMP is present, CAP binds to the DNA, increasing RNA polymerase binding and therefore increasing transcription

Eukaryotic Regulation

  • Chromatin packing:
    • Accessibility of DNA to transcription factors is influenced by how tightly the chromatin is packaged.
    • Chromatin is less tightly packaged in accessible regions
  • Transcription:
    • Multiple levels of regulation influence transcription initiation and initiation rate
  • More Regulation Levels in Eukaryotes
  • RNA processing:
    • Further steps involved in processing RNA transcripts into functional mRNA molecules affect gene expression
  • Translation and post-translation:
    • Control of protein synthesis after transcription affects gene expression
  • Chromatin accessibility is regulated by things like acetylation and deacetylation of histones

Chromatin Packaging

  • Chromatin packaging affects the accessibility of DNA to transcription factors. Loosely packaged chromatin allows for easy access, tightly packed inhibits access
  • Chromatin modifications (such as acetylation/deacetylation) can switch genes on/off

Multiple Transcription Factors

  • Transcription factors cooperate in eukaryotes
  • Multiple binding sites on DNA allowing transcription factors to interact at distant points
  • Combined effects of multiple factors affect initiation rate and efficiency in a complex fashion
  • Cooperative effects occur when distant sites interact to influence overall transcription
  • Activators and repressors in eukaryotes can work together to control gene expression in a complex fashion, leading to a rich range of possibilities and enabling a variety of cellular responses.

Cancer and Gene Regulation

  • Misregulation of cell cycle control leading to mutations and cancer
  • Oncogenes and tumor suppressor genes play a role
  • Oncogenes promote unregulated cell division
  • Tumor suppressors inhibit cell division
  • Several mutations are usually needed before a cell becomes cancerous
  • Mutations in genes controlling cell cycle control can contribute to cancer

Summary of Lecture

  • Prokaryotic regulation primarily uses operons with repressors and activators
  • Eukaryotic regulation involves chromatin packaging, transcription factors, and additional processing steps
  • Cancer results from misregulation of cell cycle control genes (oncogenes and tumor suppressors)

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BO101 Molecular Genetics Lecture 5 Control of Gene Expression 2024 PDF

Description

Explore the intricate mechanisms behind gene expression control and enzyme regulation. This quiz covers topics such as operons in prokaryotes, transcription factors in eukaryotes, and feedback inhibition in biochemical pathways. Test your knowledge of these fundamental biological processes.

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