Enzyme Regulation Overview

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Questions and Answers

What is the function of regulatory enzymes in a metabolic pathway?

  • To catalyze reactions faster than normal enzymes
  • To adjust the overall rate of the pathway (correct)
  • To serve as substrates for other enzymes
  • To perform irreversible reactions

Which enzymes are often referred to as key enzymes in metabolic pathways?

  • Enzymes that are involved in reversible reactions
  • Enzymes that are produced in large quantities
  • Enzymes that catalyze all reactions
  • Rate limiting enzymes (correct)

How does long-term regulation of enzymes occur?

  • By altering the enzyme's catalytic activity
  • By controlling the number or concentration of enzyme molecules (correct)
  • By activating all enzymes at once
  • By changing the temperature of the environment

What distinguishes short-term regulation of enzymes from long-term regulation?

<p>It occurs over seconds to minutes (A)</p> Signup and view all the answers

Which statement about the reactions catalyzed by regulatory enzymes is correct?

<p>They are usually irreversible and key to metabolic control. (C)</p> Signup and view all the answers

What process increases the rate of transcription of an enzyme's gene?

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

Which factor can act as a repressor in enzyme synthesis?

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

What is the definition of enzyme turnover?

<p>The balance between enzyme synthesis and degradation (C)</p> Signup and view all the answers

What type of regulation involves a non-covalent bond at an allosteric site?

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

Which of the following statements is true about allosteric enzymes?

<p>They exhibit cooperativity with their substrates. (A)</p> Signup and view all the answers

What role does a lack of substrate play in enzyme degradation?

<p>It makes the enzyme more susceptible to proteolysis. (A)</p> Signup and view all the answers

What best defines the process of repression in enzyme regulation?

<p>Decreasing enzyme synthesis in response to certain products. (C)</p> Signup and view all the answers

Which of the following is NOT a mechanism of catalytic regulation?

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

What is the main effect of an allosteric inhibitor on an enzyme?

<p>It changes the shape of the enzyme to prevent substrate binding. (B)</p> Signup and view all the answers

Which modification is most commonly used in reversible covalent modification of enzymes?

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

Why are zymogens released from the pancreas as inactive forms?

<p>To prevent premature activation and cell damage. (B)</p> Signup and view all the answers

What does the term 'irreversible covalent modification' refer to in enzyme regulation?

<p>Permanent alterations that prevent the enzyme from functioning. (A)</p> Signup and view all the answers

Which amino acids are commonly involved in phosphorylation processes?

<p>Serine, Threonine, and Tyrosine (C)</p> Signup and view all the answers

How does allosteric modification primarily affect enzyme activity?

<p>It induces structural changes that affect substrate binding. (B)</p> Signup and view all the answers

What is one consequence of allosteric activation of an enzyme?

<p>It can increase the enzyme's catalytic activity. (A)</p> Signup and view all the answers

What is an allosteric molecule's key characteristic?

<p>It interacts with the enzyme non-covalently. (A)</p> Signup and view all the answers

Flashcards

Regulatory enzyme

An enzyme that controls the rate of a metabolic pathway.

Metabolic pathway

A sequence of enzyme-catalyzed reactions.

Enzyme regulation

Controlling the activity of enzymes in a metabolic pathway.

Long-term regulation

Controlling enzyme concentration by changing the rate of enzyme synthesis/degradation.

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Short-term regulation

Controlling enzyme activity and not affecting the concentration or amount.

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Enzyme Induction

Increased enzyme synthesis, stimulated by an inducer (often the substrate or hormone).

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Enzyme Repression

Decreased enzyme synthesis, in response to a repressor (often the product or hormone).

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Enzyme Degradation

Breakdown of enzyme protein, altering enzyme availability.

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Allosteric Regulation

Enzyme activity changes due to binding of a molecule (effector or modifier) at a site other than the active site.

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Allosteric Enzyme

Enzyme with multiple binding sites, including an active site and an allosteric site, which affects enzyme activity.

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Enzyme Turnover

The rate of synthesis and degradation of an enzyme, which may control the number of enzyme molecules.

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Inducer

A molecule that stimulates enzyme synthesis.

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Repressor

A molecule that inhibits enzyme synthesis.

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Allosteric Inhibition

End product binding to an enzyme, causing a conformational change and inhibiting its activity.

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Allosteric Modifier

Molecule that binds to an enzyme away from the active site, affecting its activity.

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Reversible Covalent Modification

Enzyme activity changes due to addition or removal of a chemical group (like phosphate), often used to regulate activity.

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Phosphorylation

Adding a phosphate group to a protein, typically altering its enzymatic activity.

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Irreversible Covalent Modification

Enzyme activity change through irreversible chemical bonding (e.g., cleavage of a peptide).

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Zymogen

Inactive precursor of an enzyme, activated by proteolytic cleavage (breaking a protein).

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Pancreatic Enzymes

Digestive enzymes produced by the pancreas, released in inactive form (zymogens).

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Proteolytic Cleavage

The process of breaking a protein into smaller pieces by enzymatic means.

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Study Notes

Enzyme Regulation

  • Enzymes are crucial in cellular metabolism, working together in sequential pathways
  • The product of one enzyme serves as the substrate for the next in the pathway
  • Regulatory enzymes control the overall rate of these metabolic pathways to meet the cell's demands
  • The rate-limiting enzyme determines the speed of the overall pathway

Types of Enzyme Control

  • Control of enzyme quantity: This long-term regulation (hours to days) involves controlling how many enzyme molecules are present
    • Enzyme synthesis at the gene level: Induction (increasing enzyme production in response to a substrate or hormone) and repression (decreasing enzyme production in response to a repressor or product) are crucial mechanisms
    • Enzyme degradation: Loss of enzyme by proteolysis occurs when the enzyme is no longer needed
  • Control of enzyme activity (short-term): Quick changes (seconds to minutes) to the activity of enzymes are essential
    • Allosteric regulation: A molecule binds to a specific site on the enzyme, causing a shape change, altering activity
      • Feed-back inhibition: The final product of a pathway inhibits an earlier enzyme in the pathway, regulating its rate
      • Activator molecules can enhance enzyme activity.
    • Reversible covalent modification: Chemical adjustments like phosphorylation (adding a phosphate group) or dephosphorylation (removing a phosphate group) that rapidly shift enzyme activity
    • Irreversible covalent modification (proteolytic cleavage): This results in an inactive zymogen being cleaved to form an active enzyme; often involved in digestive enzymes to prevent damage to the producing cells.

Allosteric Regulation

  • Allosteric enzymes have two binding sites:
    • An active site where the substrate binds
    • An allosteric site where a regulator (effector or modifier) binds. This binding by the effector (positive or negative) alters the active site's shape, enhancing or inhibiting its catalytic activity
  • This process is often non-covalent but rapidly reversible

Feed-back Inhibition

  • End products accumulate, they bind to allosteric sites on regulatory enzymes, thereby inhibiting the enzymes and halting further synthesis in the metabolic pathway
  • This helps in regulating metabolic processes and preventing unnecessary build-up of molecules

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