CH. 3 Energy & Metabolism Notes

Energy & Metabolism

Energy Concepts

  • Work: The ability to move matter against an opposing force through energy transfer.
  • Types of Energy:
  • Kinetic Energy: Energy of motion.
  • Heat: Random motion of atoms, considered a waste product that cannot perform useful work.
  • Potential Energy: Stored energy that must be converted to kinetic energy to perform work.
  • Chemical Energy: Potential energy stored in chemical bonds (e.g., C-H bonds).

Energy Storage

  • Triglycerides: Long-term energy storage in adipose tissue (body fat).
  • Glucose: Short-term energy stored as glycogen in the liver and muscles.
  • Adenosine Triphosphate (ATP): The primary energy carrier in the cell, known as the "rechargeable battery" used continuously for energy-requiring processes.

Laws of Thermodynamics

  • 1st Law: Energy cannot be created or destroyed, only transformed from one form to another.
  • 2nd Law: In energy transformations, some energy is lost as heat, thus no conversion of energy is 100% efficient.
  • Example: Converting chemical energy in gasoline to mechanical energy in cars results in approximately 25% efficiency; the rest is lost as heat and sound.

Chemical Reactions and Metabolism

  • Metabolism: All chemical reactions in the body.
  • Chemical Reactions: Involve breaking and forming chemical bonds, rearranging atoms or molecules.
  • Chemical Equation: A notation summarizing a chemical reaction.
  • Reactants: Substances present at the beginning of a reaction.
  • Products: Substances formed as a result of a reaction.
Types of Chemical Reactions
  1. Synthesis Reactions: Combine atoms/molecules to form larger ones (e.g., 2Na + Cl2 -> 2NaCl, anabolism).
  2. Decomposition Reactions: Break down large molecules into smaller ones (e.g., lactose -> glucose + galactose, catabolism).
  3. Exchange Reactions: Atoms, molecules, or electrons are exchanged between structures (e.g., Creatine phosphate + ADP -> Creatine + ATP).
  4. Oxidation-Reduction Reactions: Involve the transfer of electrons, where oxidation is losing electrons and reduction is gaining electrons, crucial for energy production.
Energy Changes in Reactions
  • Exergonic Reactions: Release energy (e.g., glucose oxidation releasing ATP).
  • Endergonic Reactions: Require energy input (e.g., synthesizing proteins from amino acids).
ATP Cycling
  • ATP Formation: Endergonic process where ADP and phosphate combine to form ATP.
  • ATP Splitting: Exergonic process releasing energy for cellular work.
  • Cells do not store ATP; they store ADP and inorganic phosphate (P) for ATP replenishment.
Enzymes and Reaction Rates
  • Enzymes: Biological catalysts that accelerate chemical reactions by lowering activation energy (Ea).
  • Factors Influencing Reaction Rates:
  • Concentration of Enzymes and Substrates: Higher concentrations can increase reaction rates until saturation is reached.
  • Temperature: Optimal ranges (typically around 35-40°C for human enzymes); extreme temperatures can lead to denaturation.
  • pH: Enzymes have optimal pH ranges (usually 6-8); extreme pH can also lead to denaturation.
Enzyme Control Mechanisms
  • Activators: Substances that turn on enzymes.
  • Inhibitors: Substances that turn off enzymes, further classified into:
  • Competitive Inhibitors: Compete with the substrate for the active site.
  • Noncompetitive Inhibitors: Bind to another part of the enzyme, altering its shape and making it less effective.
  • Phosphorylation/Dep phosphorylation: Adding/removing phosphate groups to regulate enzymatic activity.

Metabolic Pathways

  • Series of sequential enzyme-catalyzed reactions converting substrates to products, often regulated by feedback mechanisms.

Cellular Respiration

  • Overview: Multi-step pathway to convert organic molecules (e.g., glucose) into usable energy (ATP).
  • Steps:
    1. Glycolysis: Glucose (6-C) -> 2 Pyruvate (3-C) - Anaerobic; yields 2 ATP and 2 NADH.
    2. Intermediate Stage: Converts Pyruvate into Acetyl CoA, producing 2 NADH (aerobic).
    3. Citric Acid Cycle (Krebs Cycle): Acetyl CoA -> CO2 + CoA; yields ATP, NADH, and FADH2 (aerobic).
    4. Electron Transport Chain (ETC): Uses carriers (NADH, FADH2) to generate a proton gradient to produce ATP (requires O2, aerobic).
Summary of Cellular Respiration
  • Total Yield: From glycolysis, citric acid cycle, and ETC, cellular respiration can produce about 34 ATP.
  • Anaerobic Respiration: Occurs without oxygen and primarily generates 2 ATP through lactic acid fermentation after glycolysis.

Nutrient Sources for Energy

  • Fats: Converted via glycolysis and Krebs.
  • Carbohydrates: Primary energy source through glycolysis.
  • Proteins: Degraded into amino acids and utilized for energy when necessary.

Study Concepts

  • Know the definitions and examples of kinetic energy, potential energy, chemical energy, laws of thermodynamics, enzyme roles, types of metabolic reactions, and stages of cellular respiration.
  • Understand the mechanisms of enzyme activity and regulation, including inhibitors and phosphorylation. Focus on oxidation-reduction reactions relating to cellular energy production.