Biology Chapter 6: Metabolism

Concept 6.1: Metabolism

• Metabolism: The sum of all chemical reactions in an organism; includes catabolism (breaking down molecules to release energy) and anabolism (building molecules, consuming energy).
• Catabolic Reactions: Release energy by breaking down complex molecules into simpler ones (e.g., glucose breakdown in cellular respiration).
• Anabolic Reactions: Consume energy to build complex molecules from simpler ones (e.g., protein synthesis).
• Photosynthesis: Anabolic reaction; uses light energy to synthesize glucose from CO₂ and H₂O.
• Cellular Respiration: Catabolic reaction; breaks down glucose to release energy in the form of ATP.
• Enzymes: Essential in both catabolic and anabolic reactions; lower activation energy to increase reaction rates.

Concept 6.2: Free Energy and Spontaneity

• Free Energy (G): The portion of a system's energy available to do work at constant temperature and pressure.
• Change in Free Energy (ΔG): Determines reaction spontaneity; negative ΔG indicates a spontaneous reaction (releasing energy). Positive ΔG indicates a non-spontaneous reaction (requiring energy input).
• Cellular Respiration: Exergonic (releases energy, negative ΔG).
• Photosynthesis: Endergonic (requires energy input, positive ΔG).

Concept 6.3: ATP and Energy Coupling

• ATP (Adenosine Triphosphate): Composed of adenine (nitrogenous base), ribose (five-carbon sugar), and three phosphate groups. The bond between the second and third phosphate groups is often the one broken during hydrolysis.
• Energy Coupling: The use of energy released from an exergonic reaction (e.g., ATP hydrolysis) to drive an endergonic reaction (e.g., active transport).

Concept 6.4: Enzymes and Reaction Rates

• Catalyst: Substance that speeds up a reaction without being consumed or permanently changed.
• Activation Energy (EA): Minimum energy needed to initiate a reaction.
• Enzymes: Biological catalysts that lower activation energy, speeding up reactions.
• Substrate: The reactant that binds to an enzyme.
• Active Site: Region on the enzyme where the substrate binds.
• Product: Molecules formed by the reaction.
• Enzyme Specificity: Dependent on the three-dimensional shape of the active site precisely fitting the substrate.
• Factors Affecting Enzyme Activity:
  • Substrate Concentration: Increasing substrate increases reaction rate until the enzyme is saturated.
  • pH: Each enzyme has an ideal pH range for optimal activity.
  • Temperature: Enzymatic activity increases with temperature until an optimum point is reached; beyond that, high temperatures cause denaturation.
• Denaturation: Breakdown of protein structure (hydrogen bonds and ionic interactions) due to extreme conditions affecting enzyme function.
• Competitive Inhibitors: Bind to the active site, preventing substrate binding.
• Noncompetitive Inhibitors: Bind to a site other than the active site. This changes the enzyme's shape, affecting its activity.

Concept 6.5: Enzyme Regulation

• Allosteric Regulation: Molecules bind to regulatory sites altering enzyme activity.
• Allosteric Activator: Stabilizes the active form of an enzyme, increasing its activity.
• Allosteric Inhibitor: Stabilizes the inactive form of an enzyme, decreasing its activity.
• Feedback Inhibition: Method of metabolic control; the end product of a pathway inhibits an enzyme in the pathway to prevent overproduction.

Explore the key concepts of metabolism through this quiz covering both catabolic and anabolic reactions. Test your knowledge on topics such as photosynthesis, cellular respiration, and the role of enzymes. Understand the principles of free energy and spontaneity as they relate to biological processes.