Study Notes for Chapter 6: Energy & Enzymes

Test Review: Energy & Enzymes

Chapter 6: Energy Exchanges

  1. Distinguish between the following terms:

    • Catabolism & Anabolism:

      • Catabolism: The metabolic process that breaks down molecules into smaller units, releasing energy (e.g., glycolysis).

      • Anabolism: The metabolic process that constructs molecules from smaller units, requiring energy (e.g., protein synthesis).

    • Free Energy & Entropy:

      • Free Energy (G): A measure of the usable energy available to do work in a system.

      • Entropy (S): A measure of the disorder or randomness in a system. The second law of thermodynamics states that in any energy transfer, the total entropy of a closed system always increases.

    • Exergonic & Endergonic:

      • Exergonic Reaction: A reaction that releases free energy, usually spontaneous (e.g., cellular respiration).

      • Endergonic Reaction: A reaction that absorbs free energy, non-spontaneous in nature (e.g., photosynthesis).

  2. How does feedback inhibition control a metabolic pathway?

    • Feedback inhibition is a regulatory mechanism in which the end product of a metabolic pathway inhibits an enzyme involved earlier in the pathway, preventing overproduction of the product. This regulation is crucial in maintaining homeostasis in metabolic processes.

  3. Describe the laws of thermodynamics:

    • First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed from one form to another (Conservation of Energy).

    • Second Law of Thermodynamics: In any energy transfer or transformation, the total entropy of a closed system will always increase; natural processes tend to move towards a state of greater disorder.

  4. Identify an energy profile as being endergonic or exergonic:

    • Energy Profile: A graphical representation of the energy changes during a reaction.

      • Exergonic: Characterized by a net release of energy, typically showing that the energy of the reactants is higher than that of the products.

      • Endergonic: Characterized by a net absorption of energy, typically showing that the energy of the products is higher than that of the reactants.

  5. Describe and recognize the structure of ATP:

    • Adenosine Triphosphate (ATP): Composed of an adenine base, a ribose sugar, and three phosphate groups. The high-energy bonds between the phosphate groups are key to its ability to store and transfer energy.

  6. Explain how ATP is formed and broken down; how it transfers energy and does cell work:

    • Formation: ATP is synthesized via substrates like ADP (adenosine diphosphate) and inorganic phosphate (Pi) through processes such as oxidative phosphorylation or substrate-level phosphorylation.

    • Breakdown: ATP is hydrolyzed to ADP and Pi, releasing energy for cellular work such as muscle contraction, active transport, and biosynthesis.

    • Energy Transfer: The hydrolysis of ATP into ADP and inorganic phosphate releases energy that can be utilized in various cellular processes.

Chapter 6: Enzymes

  1. Distinguish between the following terms:

    • Active Site, Allosteric Site, Substrate, Cofactor, & Coenzyme:

      • Active Site: The specific region on an enzyme where substrate molecules bind and undergo a chemical reaction.

      • Allosteric Site: A site on an enzyme where regulatory molecules can bind, changing the enzyme's shape and activity.

      • Substrate: The reactant molecule on which an enzyme acts.

      • Cofactor: A non-protein chemical compound that is necessary for the activity of an enzyme (e.g., metal ions).

      • Coenzyme: An organic molecule (often derived from vitamins) that acts as an additional helper for enzymes.

    • Competitive & Non-competitive Inhibitors:

      • Competitive Inhibitor: A molecule that resembles the substrate and competes for binding at the active site, reducing enzyme activity.

      • Non-competitive Inhibitor: A molecule that binds to an allosteric site, changing the enzyme structure and inhibiting its activity regardless of substrate concentration.

    • Activators & Inhibitors:

      • Activators: Molecules that increase enzyme activity, enhancing substrate binding or catalysis.

      • Inhibitors: Molecules that decrease enzyme activity, either by competitive or non-competitive binding.

  2. Describe enzyme structure & characteristics:

    • Enzymes are typically globular proteins that have a specific 3D structure crucial for their function. They reduce the activation energy of chemical reactions and facilitate processes by providing an active site for substrate binding.

  3. Explain how enzymes work (Induced Fit):

    • The Induced Fit Model explains that the active site of an enzyme changes shape to fit the substrate once binding occurs, enhancing the enzyme's ability to catalyze the reaction efficiently.

  4. Describe factors that affect enzyme action:

    • Substrate Concentration: Increased substrate concentration generally leads to increased reaction rate until the enzyme is saturated.

    • Enzyme Concentration: More enzymes lead to increased reaction rates, provided sufficient substrate is available.

    • Temperature: Enzymes have optimal temperature ranges; too high or too low can denature the enzyme or slow activity.

    • pH: Each enzyme has an optimal pH; deviations can result in decreased activity or denaturation.

  5. Explain how enzymes are regulated:

    • Enzymes are regulated by inhibitors and activators, which can modify their activity. Feedback inhibition serves as a vital regulatory mechanism to ensure metabolic pathways are balanced according to cellular needs.

  6. Be able to calculate the rate of a chemical reaction:

    • Rate of Reaction Formula:
      Rate = \frac{\text{Change in amount of Product (or Substrate)}}{\text{Change in time}}

    • This formula allows for the calculation of a reaction's speed by measuring the change in concentration of a product or substrate over time.