Mechanism of Enzyme Action
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Mechanism of Enzyme Action

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Questions and Answers

Which of the following accurately describes the lock-and-key model of enzyme action?

  • The substrate binds to multiple enzymes at the same time.
  • Enzymes bind with any substrate regardless of compatibility.
  • Each enzyme has a specific active site that exactly matches a specific substrate. (correct)
  • Enzymes and substrates can change shape to fit each other.

    • Enzymes decrease the reaction rate by raising activation energy.

    False

    What is the role of enzymes in biological reactions?

    Enzymes catalyze reactions by lowering the activation energy and increasing reaction rates.

    The ________ model describes how enzymes can change shape to better accommodate a substrate during binding.

    <p>induced-fit</p> Signup and view all the answers

    Match the following enzyme properties to their descriptions:

    <p>Active Site = The location on the enzyme where the substrate binds Activation Energy = The energy required to initiate a reaction Substrate = The molecule upon which an enzyme acts Enzyme-Substrate Complex = The temporary complex formed when an enzyme binds to its substrate</p> Signup and view all the answers

    How do enzymes stabilize the transition state during a reaction?

    <p>By reducing the energy required to reach the transition state.</p> Signup and view all the answers

    Once an enzyme catalyzes a reaction, it becomes permanently altered.

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

    What is meant by the term 'catalysis' in the context of enzyme function?

    <p>Catalysis refers to the process by which enzymes increase the rate of a chemical reaction without being consumed.</p> Signup and view all the answers

    What is the primary role of RNA?

    <p>Protein synthesis and gene expression</p> Signup and view all the answers

    DNA is single-stranded in its structure.

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

    What are the three types of RNA and their primary functions?

    <p>mRNA (carries instructions), tRNA (delivers amino acids), rRNA (part of ribosome structure)</p> Signup and view all the answers

    Enzymes lower the ______ needed for chemical reactions to occur.

    <p>activation energy</p> Signup and view all the answers

    Match the types of RNA with their functions:

    <p>mRNA = Carries genetic instructions from DNA tRNA = Delivers amino acids to ribosomes rRNA = Forms part of the ribosome's structure siRNA = Regulates gene expression by silencing mRNA</p> Signup and view all the answers

    Which statement best describes the induced-fit model of enzyme action?

    <p>The substrate alters the shape of the enzyme upon binding.</p> Signup and view all the answers

    Enzymes are not affected by temperature and pH changes.

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

    What is the difference between the lock-and-key model and the induced-fit model?

    <p>The lock-and-key model implies a rigid structure while the induced-fit model allows for enzyme conformation change.</p> Signup and view all the answers

    What does the substrate must do to form an enzyme-substrate complex in the lock-and-key model?

    <p>Fit precisely into the enzyme's active site</p> Signup and view all the answers

    The induced-fit model states that the enzyme's active site is rigid and unchanging.

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

    Name an enzyme that exemplifies the induced-fit model.

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

    In the lock-and-key model, the enzyme acts as a 'lock' and the substrate acts as the _______.

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

    Which of the following statements accurately describes the role of enzymes in chemical reactions?

    <p>Enzymes lower the activation energy.</p> Signup and view all the answers

    Match the following enzyme concepts with their explanations:

    <p>Lock-and-key model = Substrate fits precisely into active site Induced-fit model = Active site molds around substrate upon binding Activation energy = Energy required to start a reaction Enzyme inhibitor = Reduces enzyme activity by binding to the enzyme</p> Signup and view all the answers

    The lock-and-key model can explain the flexibility of enzymes when interacting with different substrates.

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

    Enzymes can increase ___________ by adjusting their active sites during the reaction process.

    <p>catalytic efficiency</p> Signup and view all the answers

    Study Notes

    Mechanism of Enzyme Action

    • Enzymes have an active site, a specific region where the substrate binds.
    • This active site is complementary to the substrate, allowing for lock-and-key or induced fit interactions.

    Lowering Activation Energy

    • Enzymes lower activation energy by facilitating a favorable environment for reactions.
    • This involves:
      • Orienting substrates: enzymes position substrates in the optimal arrangement.
      • Straining substrate bonds: enzymes put strain on bonds within the substrate making them easier to break.
      • Providing an alternative reaction pathway: bypasses high-energy steps, requiring less overall energy.
      • Stabilizing transition states: stabilizes the high-energy transition state of a reaction, allowing it to proceed more easily.

    Catalysis and Product Release

    • Once the reaction occurs, the enzyme releases the products and is ready for new substrates.
    • Enzymes are not consumed during reactions, allowing them to repeat their catalytic role.

    Impact of Lowering Activation Energy

    • By lowering activation energy, enzymes increase the reaction rate significantly.
    • This enables essential life processes like digestion, DNA replication, and cellular respiration to occur at a sufficient rate.

    Lock-and-Key Model

    • In the lock-and-key model, the active site of the enzyme has a specific shape that only fits a particular substrate.
    • The substrate fits perfectly into the active site without any alteration in shape, forming the enzyme-substrate complex.
    • Once bound, the enzyme catalyzes the reaction by lowering activation energy, allowing the substrate to be converted into the product(s).
    • This model is effective for enzymes with highly specific substrate requirements, such as sucrase, which only binds sucrose.

    Induced-Fit Model

    • In the induced-fit model, the enzyme's active site is flexible and conforms to the substrate upon binding, creating a snug fit.
    • The active site molds itself around the substrate, strengthening the interaction and positioning the substrate optimally for the reaction.
    • This allows the enzyme to better stabilize the transition state, reducing activation energy and promoting the chemical reaction.
    • This model is observed in enzymes such as hexokinase, which alters its shape to bind glucose tightly.

    DNA & RNA Comparisons

    • DNA: exists as a stable double helix, storing and protecting genetic information.
    • RNA: exists in various forms with specific functions:
      • mRNA: carries instructions from DNA to ribosomes for protein synthesis.
      • tRNA: delivers amino acids to ribosomes for protein assembly based on the mRNA sequence.
      • rRNA: forms part of the ribosome's structure, catalyzing peptide bond formation.

    Complementary Base Pairing

    • DNA:

      • Adenine (A) pairs with Thymine (T) via two hydrogen bonds.
      • Cytosine (C) pairs with Guanine (G) via three hydrogen bonds.

    • RNA:

      • Adenine (A) pairs with Uracil (U) via two hydrogen bonds.
      • Cytosine (C) pairs with Guanine (G) via three hydrogen bonds.

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    SBI4U Unit 1 Biochemistry Test Review Package PDF

    Description

    Explore the fascinating mechanisms of enzyme action in this quiz. Learn how enzymes facilitate reactions by lowering activation energy and stabilizing transition states. Test your understanding of active sites, substrate interactions, and the overall catalytic process.

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