Thermodynamics and Free Energy Quiz
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Questions and Answers

What is the initial energy required to start a chemical reaction called?

  • Activation energy (correct)
  • Free energy change
  • Thermal energy
  • Bond energy

    • How do enzymes affect chemical reactions?

  • They convert the products into reactants.
  • They lower the activation energy barrier. (correct)
  • They alter the reactants involved in the reaction.
  • They increase the reaction's free energy change.

    • What form of energy is often supplied to reactants to overcome the activation energy barrier?

  • Electrical energy
  • Thermal energy (correct)
  • Nuclear energy
  • Chemical energy

    • What is indicated by the symbol ∆G in a chemical reaction?

    <p>Change in free energy</p> Signup and view all the answers

    What is true about the effect of enzymes on the energy profile of a reaction?

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

    What is the optimal temperature for a typical human enzyme?

    <p>37°C</p> Signup and view all the answers

    Which of the following is a characteristic of cofactors?

    <p>They are essential for enzyme activity.</p> Signup and view all the answers

    Which enzyme has an optimal pH in the stomach?

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

    What type of inhibitor binds to the active site of an enzyme?

    <p>Competitive inhibitor</p> Signup and view all the answers

    Which of the following statements is true about coenzymes?

    <p>They include vitamins.</p> Signup and view all the answers

    What effect do noncompetitive inhibitors have on enzymes?

    <p>They change the enzyme's shape.</p> Signup and view all the answers

    What is the optimal temperature for the enzyme of thermophilic bacteria?

    <p>77°C</p> Signup and view all the answers

    Which of the following is an example of enzyme inhibitors?

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

    What happens to the entropy of the universe during every energy transfer or transformation?

    <p>It increases as some energy becomes unusable.</p> Signup and view all the answers

    What does a negative free-energy change (∆G) indicate about a chemical reaction?

    <p>The reaction occurs spontaneously.</p> Signup and view all the answers

    Which of the following statements is true regarding the second law of thermodynamics?

    <p>Entropy may decrease in an organism but overall entropy increases.</p> Signup and view all the answers

    In the context of free energy, what does the term 'free energy' (G) represent?

    <p>Energy available to do work in a living system.</p> Signup and view all the answers

    Which equation shows the relationship between changes in free energy, enthalpy, and entropy?

    <p>∆G = ∆H - T∆S</p> Signup and view all the answers

    Why do biologists study free-energy changes in reactions?

    <p>To identify whether the reactions are spontaneous or require energy input.</p> Signup and view all the answers

    What aspect of energy transformations is emphasized in the second law of thermodynamics?

    <p>There is always a loss of some usable energy as heat.</p> Signup and view all the answers

    When considering a spontaneous process, which of the following must be true?

    <p>The change in free energy (∆G) is negative.</p> Signup and view all the answers

    What is the primary role of isoleucine in the feedback inhibition of threonine synthesis?

    <p>It binds to the allosteric site of enzyme 1.</p> Signup and view all the answers

    In the context of feedback inhibition, what happens when isoleucine is used up by the cell?

    <p>Enzyme 1 can continue catalyzing threonine.</p> Signup and view all the answers

    What is a potential consequence of feedback inhibition in metabolic pathways?

    <p>It prevents overproduction of isoleucine.</p> Signup and view all the answers

    Where are enzymes for cellular respiration primarily located in eukaryotic cells?

    <p>In the mitochondria</p> Signup and view all the answers

    What best describes the role of structures within the cell regarding metabolic pathways?

    <p>They help organize metabolic pathways.</p> Signup and view all the answers

    What happens to the active site of enzyme 1 during feedback inhibition when isoleucine binds?

    <p>It is blocked from catalyzing threonine to intermediate A.</p> Signup and view all the answers

    What is the significance of enzyme localization within different organelles?

    <p>It ensures enzymes are available for specific reactions.</p> Signup and view all the answers

    Which intermediate is formed directly by the enzymatic activity of enzyme 1?

    <p>Intermediate A</p> Signup and view all the answers

    What does an enzyme do to the activation energy of a reaction?

    <p>It lowers the activation energy required for the reaction.</p> Signup and view all the answers

    What is formed when an enzyme binds to its substrate?

    <p>An enzyme-substrate complex.</p> Signup and view all the answers

    What is the primary role of the active site in an enzyme?

    <p>To facilitate the binding of substrates.</p> Signup and view all the answers

    Which of the following describes the process that helps an enzyme to catalyze a reaction?

    <p>Bringing chemical groups of the active site into close proximity.</p> Signup and view all the answers

    How can an active site enhance reaction catalysis?

    <p>By stabilizing the transition state.</p> Signup and view all the answers

    Which of the following statements about enzymes is FALSE?

    <p>An enzyme can act on multiple types of substrates simultaneously.</p> Signup and view all the answers

    What is one way that the active site of an enzyme lowers the activation energy?

    <p>By orienting substrates in a manner that favors the reaction.</p> Signup and view all the answers

    What remains unchanged after an enzymatic reaction?

    <p>The enzyme.</p> Signup and view all the answers

    Study Notes

    Second Law of Thermodynamics

    • Every energy transfer or transformation results in some unusable energy, often lost as heat
    • Increases entropy (disorder) of the universe
    • Evolution of complex organisms doesn't violate the second law
    • An organism's entropy might decrease, but the universe's overall entropy increases

    Free-Energy Change

    • A living system's free energy is energy capable of doing work under uniform temperature and pressure (like a living cell)
    • ΔG represents the change in free energy during a process
    • Related to:
      • ΔH: change in total energy
      • ΔS: change in entropy
      • T: temperature in Kelvin
    • Formula: ΔG = ΔH – TΔS
    • Only negative ΔG indicates spontaneous processes
    • Spontaneous processes can be harnessed for work

    Activation Energy

    • Every chemical reaction involves bond breaking and forming
    • Activation energy (EA) is the initial energy required to start a chemical reaction
    • Often supplied as thermal energy absorbed by reactant molecules from surroundings

    Enzymes Lowering the EA Barrier

    • Enzymes are biological catalysts that speed up reactions by lowering the EA barrier
    • They don't affect the change in free energy (ΔG), but hasten reactions that would eventually occur

    Enzyme Substrate Specificity

    • The reactant an enzyme acts on is its substrate
    • Enzyme binds to substrate forming an enzyme-substrate complex
    • The active site is the region on the enzyme where the substrate binds
    • Induced fit of a substrate positions active site chemical groups to enhance catalysis

    Catalysis in the Enzyme's Active Site

    • Substrate binds to the enzyme's active site
    • The active site lowers the EA barrier by:
      • Orienting substrates correctly
      • Straining substrate bonds
      • Providing a favorable microenvironment
      • Covalently bonding to the substrate

    Enzyme Activity Factors: Temperature and pH

    • Each enzyme has an optimal temperature for activity (e.g., 37°C for typical human enzyme)
    • Optimal pH varies per enzyme (e.g., pepsin in the stomach vs. trypsin in the intestines)

    Cofactors

    • Nonprotein enzyme helpers
    • Can be either inorganic (e.g., metal ions) or organic
    • Organic cofactors are called coenzymes
    • Vitamins are examples of coenzymes

    Enzyme Inhibitors

    • Competitive inhibitors bind to the active site, competing with the substrate
    • Noncompetitive inhibitors bind elsewhere, causing the enzyme to change shape and reducing active site effectiveness
    • Examples include toxins, poisons, pesticides, and antibiotics

    Feedback Inhibition

    • Regulates metabolic pathways by preventing overproduction of end products
    • The end product acts as an inhibitor to an earlier enzyme in the pathway, halting further product synthesis

    Specific Localization of Enzymes

    • Cellular structures organize metabolic pathways
    • Some enzymes are structural components in membranes
    • Eukaryotic cells have enzymes in specific organelles (e.g., cellular respiration enzymes in mitochondria)

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    MBG111 L8-An Introduction to Metabolism PDF

    Description

    Test your understanding of the Second Law of Thermodynamics, free-energy change, and activation energy. This quiz covers key concepts such as entropy, free energy calculations, and the role of activation energy in chemical reactions. Perfect for students studying thermodynamics in biology or chemistry.

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