Biology Chapter on Gene Expression
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Questions and Answers

Prokaryotes and eukaryotes control gene expression in response to ___________________________ and physiological conditions.

environmental

Which term refers to genes that are expressed continuously at a relatively constant rate?

  • Housekeeping Genes (correct)
  • Operons
  • Activators
  • Repressors

Repressors are biochemical molecules that promote gene expression.

False (B)

What is an operon?

<p>A group of genes clustered together that are regulated by one promoter.</p> Signup and view all the answers

Which of the following is a regulatory region where RNA polymerase binds in an operon?

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

The lac operon is primarily used to regulate the metabolism of glucose.

<p>False (B)</p> Signup and view all the answers

Activators are biochemical molecules that ___________________ gene expression.

<p>promote</p> Signup and view all the answers

Match the terms to their descriptions:

<p>Gene Regulation = The control and change of gene expression in response to different conditions Activators = Biochemical molecules that promote gene expression Repressors = Biochemical molecules that reduce gene expression Operon = A group of genes clustered together that are regulated by one promoter</p> Signup and view all the answers

What is the function of the lac operon?

<p>To produce proteins that metabolize lactose (B)</p> Signup and view all the answers

The lac repressor protein is only produced when lactose is present in the cell.

<p>False (B)</p> Signup and view all the answers

What role does CAP play in the regulation of the lac operon?

<p>CAP promotes transcription by helping RNA polymerase bind to the promoter.</p> Signup and view all the answers

What is the role of cAMP in the lac operon?

<p>It binds to CAP, allowing CAP to bind DNA and promote transcription. (D)</p> Signup and view all the answers

The lac operon is considered an ______ operon.

<p>inducible</p> Signup and view all the answers

The trp repressor binds to the operator when tryptophan is absent.

<p>False (B)</p> Signup and view all the answers

What two conditions must be met for the lac operon to be expressed?

<p>Glucose is not available and lactose is available (C)</p> Signup and view all the answers

What is the main purpose of gel electrophoresis?

<p>To separate DNA fragments based on their size.</p> Signup and view all the answers

In humans, tryptophan is used to make melatonin and ______.

<p>serotonin</p> Signup and view all the answers

Match the following regulatory elements with their functions in the lac operon:

<p>Promoter = Site where transcription begins Operator = Sequence that controls transcription Repressor = Protein that inhibits transcription CAP binding site = Site where a protein that promotes transcription binds</p> Signup and view all the answers

Match the following molecules with their function in the context of the lac operon:

<p>cAMP = Binds to CAP and allows CAP to promote transcription Allolactose = Inactivates the lac repressor CAP = Binds to DNA to promote transcription</p> Signup and view all the answers

Allolactose is a molecule that inhibits the expression of the lac operon.

<p>False (B)</p> Signup and view all the answers

What molecules do the lac repressor and CAP sense, respectively?

<p>The lac repressor is a lactose sensor and CAP is a glucose sensor.</p> Signup and view all the answers

How does the presence of lactose affect the lac operon?

<p>It is converted to allolactose, which inactivates the lac repressor. (B)</p> Signup and view all the answers

The trp operon encodes enzymes necessary for the production of glucose.

<p>False (B)</p> Signup and view all the answers

How many genes are located on the trp operon that are used by E. coli to create tryptophan?

<p>5</p> Signup and view all the answers

What is the role of tryptophan in the trp operon when levels are high?

<p>It acts as a corepressor, binding to the repressor to activate it. (C)</p> Signup and view all the answers

The gene trpR is part of the trp operon.

<p>False (B)</p> Signup and view all the answers

What is a corepressor?

<p>A small molecule that activates a repressor.</p> Signup and view all the answers

The trp operon is a _________ operon.

<p>repressible</p> Signup and view all the answers

Which of the following is NOT a level at which gene expression is controlled in eukaryotes?

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

General transcription factors in eukaryotes bind to the operator region.

<p>False (B)</p> Signup and view all the answers

What two roles does the trp repressor act as?

<p>A sensor and a switch.</p> Signup and view all the answers

Match the following gene control mechanisms with their descriptions:

<p>Transcriptional = Controls DNA to mRNA synthesis rate Post-Transcriptional = Processes mRNA Translational = Controls protein synthesis Post-Translational = Modifies synthesized proteins</p> Signup and view all the answers

What is a key mechanism of translational regulation that impacts mRNA’s ability to be translated into a protein?

<p>Changes in the length of the poly(A) tail of the mRNA molecule (A)</p> Signup and view all the answers

All proteins produced by the cell are immediately active and ready to perform their functions.

<p>False (B)</p> Signup and view all the answers

Name three ways a protein can be regulated after it has been produced?

<p>Processing, Chemical Modification, and Degradation</p> Signup and view all the answers

A mass of undifferentiated cells that can form if the cell does not follow normal cell division is called a ______.

<p>tumour</p> Signup and view all the answers

A malignant tumor is characterized by which of the following?

<p>The ability to invade surrounding tissue (D)</p> Signup and view all the answers

Mutations in a cell will be passed on to nearby cells, as well as daughter cells.

<p>False (B)</p> Signup and view all the answers

How does the degradation of a protein relate to gene expression?

<p>The rate of degradation affects the rate at which gene products are available.</p> Signup and view all the answers

Match the following types of tumors with their characteristics:

<p>Benign tumor = Grows slowly, stays in place, and does not return after removal Malignant tumor = Grows uncontrollably, invades other tissues, and affects normal functions of an organism</p> Signup and view all the answers

What is the role of general transcription factors in gene transcription?

<p>To bind to the promoter region and provide a substrate for RNA polymerase (B)</p> Signup and view all the answers

Adding methyl groups to histones loosens their association with DNA, thus promoting transcription.

<p>False (B)</p> Signup and view all the answers

In agouti mice, what is the result of the agouti gene being methylated?

<p>The agouti gene is silenced which leads to a normal healthy mouse.</p> Signup and view all the answers

The complex consisting of general transcription factors and RNA polymerase is known as the transcription ________ complex.

<p>initiation</p> Signup and view all the answers

Match the following terms with their effect on gene expression:

<p>Acetylation of histones = Loosens DNA association and promotes transcription Methylation of cytosine bases = Inhibits transcription Masking proteins binding to mRNA = Prevents protein translation Hormone affecting mRNA degradation = Changes rate of mRNA breakdown</p> Signup and view all the answers

What is a consequence of the agouti gene being ‘on’ in mice?

<p>Increased risk of cancer and diabetes. (B)</p> Signup and view all the answers

Post-transcriptional regulation only involves changes in pre-mRNA processing.

<p>False (B)</p> Signup and view all the answers

What is the effect of masking proteins binding to mRNA?

<p>They prevent protein translation</p> Signup and view all the answers

Flashcards

Gene Regulation

The control and change of gene expression in response to different conditions in the cell or environment. This determines cell fates.

Housekeeping Genes (Constitutive)

Genes that are expressed all the time, only varying in rate of expression. These genes are required for homeostasis.

Activators

Biochemical molecules that promote gene expression.

Repressors

Biochemical molecules that reduce gene expression.

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Operon

A group of genes clustered together that are regulated by one promoter.

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Promoter

A region of DNA where RNA polymerase binds to initiate transcription.

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Operator

A region of DNA where regulatory proteins bind to control gene expression.

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Enhancer

A region of DNA that can enhance transcription.

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What is the lac operon?

A group of genes that work together to break down lactose in bacteria, controlled by a regulatory system.

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What is an inducer?

A molecule that binds to the lac repressor and changes its shape, preventing it from binding to the operator.

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What is the lac repressor?

A protein that binds to the operator region of the lac operon and blocks transcription.

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How is the lac operon regulated?

The lac operon is regulated by both lactose and glucose levels. Transcription only occurs when lactose is present and glucose is absent.

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What is the catabolite activator protein (CAP)?

A protein that binds to the CAP binding site upstream of the lac operon. When bound, it enhances transcription.

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How does allolactose regulate the lac operon?

A modified form of lactose, allolactose, acts as an inducer for the lac operon. It binds to the lac repressor, causing it to release from the operator and allowing transcription.

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What kind of operon is the lac operon?

The lac operon is an inducible operon. It is only active when the inducer (allolactose) is present. This means that the genes are only expressed when lactose is available.

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How does CAP sense glucose levels?

When glucose is present, CAP is not bound to the CAP binding site, reducing transcription. When glucose is absent, CAP binds to the site, promoting transcription.

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Lac Operon

A regulatory mechanism in bacteria that controls the expression of genes involved in lactose metabolism.

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Allolactose

A small molecule produced inside bacterial cells when lactose is present.

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Lac Repressor

A regulatory protein that binds to the operator region of the Lac Operon, preventing transcription of lactose-utilizing genes.

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CAP (Catabolite Activator Protein)

A protein that binds to DNA in the presence of cAMP, promoting the transcription of genes.

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cAMP (cyclic AMP)

A molecule that acts as a signal of low glucose levels in bacteria. It binds to CAP, activating it.

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Trp Operon

A regulatory mechanism in bacteria that controls the expression of genes involved in tryptophan biosynthesis.

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Trp Repressor

A regulatory protein that binds to the operator region of the Trp Operon, preventing transcription of tryptophan-synthesizing genes.

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Melatonin

A hormone that helps regulate sleep and wake cycles.

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Corepressor

A molecule that binds to a repressor protein and changes its shape so that it can bind to the operator and prevent transcription.

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Repressible Operon

A type of operon that is usually on but can be turned off by a repressor protein bound to its operator.

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Repressor Gene

A gene that encodes a repressor protein, which can bind to the operator of an operon and prevent transcription.

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Transcriptional Regulation

The mechanism by which genes are controlled through the regulation of transcription. It dictates which genes are transcribed, and how much transcript is produced.

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Translational Regulation

A type of regulation that occurs before the protein is synthesized during the process of translation. It can affect the amount of protein produced.

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Post-Translational Regulation

A type of regulation that occurs after the protein has been synthesized. This regulation often involves modifications to the protein's activity or stability.

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General Transcription Factors

Proteins that bind to DNA and help RNA polymerase initiate transcription.

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Transcriptional regulatory elements

Specific DNA sequences that act as binding sites for proteins involved in gene regulation, promoting or suppressing transcription.

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Histone acetylation

The process of adding acetyl groups to histone proteins, which loosens their association with DNA and makes genes more accessible for transcription.

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DNA methylation

The process of adding methyl groups to cytosine bases in promoter regions, which can inhibit transcription by making the DNA less accessible to transcription machinery.

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Alternative splicing

A post-transcriptional regulatory mechanism involving the removal of introns and the joining of exons in different combinations, leading to the production of multiple protein isoforms from a single gene.

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Binding of masking proteins

A post-transcriptional regulatory mechanism where proteins bind to mRNA and prevent its translation into protein.

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mRNA degradation rate

A post-transcriptional regulatory mechanism affecting the stability and lifespan of mRNA molecules, influencing the amount of protein produced from a given mRNA transcript.

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Regulation of mRNA degradation

A process influencing the rate at which an mRNA transcript is broken down, which in turn affects protein production. This can be influenced by hormones and other regulatory molecules.

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Poly(A) Tail Regulation

A process that regulates the length of the poly(A) tail on mRNA molecules, affecting their stability and lifespan, influencing how long they remain in the cell and how much protein they produce. This control over the translation process ensures efficient and accurate protein production.

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Cancer

A disease characterized by uncontrolled cell growth and the ability of abnormal cells to invade other tissues. It often arises from mutations in genes responsible for regulating cell division, leading to abnormal cell growth and proliferation.

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Gel Electrophoresis

The process of separating DNA fragments based on their size and charge using an electric current. Smaller fragments move further and faster through a gel matrix.

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Protein Processing

An inactive protein that is converted into an active form through the removal of specific regions. This processing step is crucial for activating the protein's function.

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Chemical Modification of Proteins

The addition or removal of chemical groups to proteins, modifying their activity and function. These modifications allow for dynamic control of protein behavior within the cell.

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Protein Degradation

The breakdown of proteins into their amino acid components. This process is essential for removing damaged or no longer needed proteins, ensuring proper cellular function and maintaining balance.

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Tumor

A mass of undifferentiated cells that often results from abnormal cell division. Benign tumors typically grow slowly and remain localized, while malignant tumors are cancerous and can invade other tissues.

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Study Notes

Gene Regulation in Prokaryotes and Eukaryotes

  • Gene regulation is the control and alteration of gene expression in response to various environmental and physiological conditions. This also dictates cell fates.
  • Genes aren't always needed for transcription or translation, which would be inefficient if all genes were constantly active. Instead, prokaryotes and eukaryotes control gene expression in response to conditions.
  • A prime example is insulin production in humans. Insulin is only needed when blood glucose levels are high; otherwise, insulin production is not required.
  • Organism function relies on turning genes "on" and "off" as needed.

Definitions

  • Gene Regulation: Control and modification of gene expression in response to cell or environment conditions. This also impacts cell development.
  • Housekeeping Genes (Constitutive): Genes consistently expressed, only varying in expression rate. These are essential for homeostasis.
  • Activators: Biochemical molecules that increase gene expression.
  • Repressors: Biochemical molecules that reduce gene expression.
  • Operon: A cluster of genes regulated by a single promoter, often found together.

Prokaryotic Gene Control Mechanisms (Operons)

  • Operon : A group of genes clustered together, controlled by a single promoter. This is found in prokaryotes.
  • Structure : Regulatory regions (enhancer, promoter, operator) and coding regions (genes).
    • The enhancer activates transcription to higher levels.
    • The promoter is the RNA polymerase binding site.
    • The operator region is where regulatory factors (e.g., repressors) bind.

The Lac Operon

  • Lactose is a potential energy source for bacteria.
  • Prokaryotes utilize the lac operon to control gene expression of lactose-metabolizing proteins.
  • Preference for glucose is shown, and lactose use is favored when glucose levels are low.
  • The lac operon is a group of three genes (lacZ, lacY, lacA) necessary for lactose metabolism. It has a promoter, operator, and coding regions for enzymes responsible for lactose breakdown.
  • The lac operon has a positive regulatory site, where the catabolite activator protein (CAP) binds. The binding of CAP activates transcription by promoting RNA polymerase binding to the promoter.
  • There is a repressor protein (lac repressor) that controls gene expression. Its presence prevents gene expression if lactose is not available.
  • Allolactose, the inducer, is produced from lactose and binds to the repressor protein, causing it to detach from the operator. This enables transcription of the lac operon genes.

The Trp Operon

  • Bacteria (e.g., E. coli) require amino acids to live. Tryptophan is one such amino acid.
  • Tryptophan is vital for making melatonin and serotonin in humans.
  • Bacteria acquire tryptophan if available from the environment; otherwise, they produce it using enzymes encoded by five genes found together in the trp operon.
  • The trp operon has a repressor protein that's constantly transcribed.
  • Tryptophan acts as a corepressor to bind to the repressor, activating it and blocking transcription.
  • Low tryptophan levels lead to repressor inactivation, promoting operon transcription.

Eukaryotic Gene Control Mechanisms

  • Eukaryotic gene regulation occurs in transcription and translation, including these steps.
  • Transcriptional Regulation: Control of gene transcription (pre-mRNA synthesis). Mechanisms in this stage include:
    • Promoter/enhancer elements and chromatin remodeling.
    • General transcription factors help RNA polymerase bind to DNA to begin transcription.
    • Chemical changes like acetylation and methylation of histones and DNA.
  • Post-transcriptional Regulation: Modification of pre-mRNA during processing. Mechanisms may include:
    • Alternative splicing, mRNA degradation rate changes.
  • Translational Regulation: Regulation of protein synthesis (mRNA to protein). Includes:
    • Changes in mRNA length (poly(A) tail alteration).
  • Post-translational Regulation: Modification of proteins after synthesis. Includes:
    • Processing, chemical additions/deletions, degradation rate.

DNA Packaging

  • DNA in eukaryotic cells is tightly packaged around histone proteins forming nucleosomes. These further compact into higher-order structures.

Cancer

  • Cancer can arise from abnormal gene regulation, leading to uncontrolled cell growth and division. This arises from accumulated mutations, and can be more common in older people. Mutations can alter promoter regions, protein-coding regions, and introduce foreign DNA from viruses.

Gel Electrophoresis

  • A technique to separate DNA fragments based on size. Fragments move in an electric field through a gel. Larger fragments move slower and smaller ones faster.
  • This technique can be used to detect mutations or changes in DNA based on differences in the apparent fragment length.

Other Information

  • Include the additional stages and details discussed.

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Test your knowledge on gene expression in prokaryotes and eukaryotes with this quiz. Explore concepts such as operons, repressors, and the lac operon while assessing your understanding of gene regulation mechanisms. Ideal for biology students looking to solidify their comprehension of gene control.

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