Basics of Metabolism and Energy

Overview

This lecture covers the fundamentals of metabolism, energy forms, thermodynamics laws, free energy, ATP, enzymes, and regulation of metabolic pathways.

Metabolism and Metabolic Pathways

• Metabolism is the sum of all chemical reactions in an organism.
• A metabolic pathway modifies a specific molecule in sequential steps, each catalyzed by a specific enzyme.
• Catabolic pathways break down complex molecules, releasing energy (e.g., cellular respiration).
• Anabolic pathways build complex molecules, consuming energy (e.g., protein synthesis).

Forms and Transformations of Energy

• Energy is the capacity to cause change and exists in many forms.
• Kinetic energy is energy of motion; thermal energy is molecular motion contributing to heat.
• Potential energy is stored due to location or structure; chemical energy is a form of potential energy stored in molecular bonds.
• Energy can be converted between forms, such as potential to kinetic.

Thermodynamics in Biological Systems

• Organisms are open systems, exchanging energy and matter with their surroundings.
• The First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed.
• The Second Law of Thermodynamics: Every energy transfer increases the entropy (disorder) of the universe.

Free Energy and Spontaneity

• Free energy (G) of a system can do work when temperature and pressure are uniform.
• A negative ΔG (change in free energy) indicates a spontaneous process; positive ΔG means nonspontaneous.
• Spontaneous does not mean fast; it means energetically favorable.

Gibbs Free Energy Equation

• The equation ΔG = ΔH - TΔS relates free energy change to changes in enthalpy (ΔH), entropy (ΔS), and temperature (T).
• Exergonic (exergonic) reactions: negative ΔG, spontaneous, release energy.
• Endergonic (endergonic) reactions: positive ΔG, nonspontaneous, require energy input.

ATP: The Cell’s Energy Currency

• ATP (adenosine triphosphate) consists of adenine, ribose, and three phosphate groups.
• Hydrolysis of ATP releases energy by breaking the terminal phosphate bond, resulting in ADP and inorganic phosphate (Pi).
• ATP hydrolysis drives cellular work by coupling exergonic and endergonic reactions.

Enzymes and Catalysis

• Enzymes are protein catalysts that speed up specific reactions without being consumed.
• Enzymes lower the activation energy required for reactions to occur.
• Each enzyme is specific for its substrate, binding at the active site and forming an enzyme-substrate complex.

Environmental Effects and Regulation

• Enzymes have optimal temperature and pH for activity; extremes can denature them.
• Some enzymes require nonprotein helpers called cofactors (inorganic) or coenzymes (organic, e.g., vitamins).
• Inhibitors reduce enzyme activity: competitive inhibitors bind the active site, non-competitive inhibitors bind elsewhere, altering enzyme function.

Metabolic Pathway Regulation

• Allosteric regulation occurs when a molecule binds a site other than the active site, affecting enzyme function.
• Feedback inhibition occurs when the end product of a pathway inhibits an earlier step to prevent overproduction.

Key Terms & Definitions

• Metabolism — All of an organism’s chemical reactions.
• Catabolic Pathway — Breaks down molecules, releasing energy.
• Anabolic Pathway — Builds molecules, consuming energy.
• Kinetic Energy — Energy of motion.
• Potential Energy — Stored energy due to position or structure.
• Entropy (S) — Measure of disorder or randomness.
• Enthalpy (H) — Total energy, often associated with heat.
• Free Energy (G) — Energy available to do work in a system.
• Exergonic Reaction — Releases energy, spontaneous (ΔG < 0).
• Endergonic Reaction — Absorbs energy, nonspontaneous (ΔG > 0).
• ATP — Adenosine triphosphate, main cellular energy carrier.
• Enzyme — Protein catalyst speeding up reactions.
• Cofactor — Nonprotein enzyme helper (e.g., minerals).
• Coenzyme — Organic cofactor (e.g., vitamins).
• Competitive Inhibitor — Blocks active site of enzyme.
• Non-Competitive Inhibitor — Binds elsewhere, alters enzyme shape/function.
• Allosteric Regulation — Regulation of enzyme by binding to a non-active site.
• Feedback Inhibition — End product of a pathway shuts down its own production.

Action Items / Next Steps

• Review the Gibbs free energy equation and practice identifying reaction types (exergonic vs. endergonic).
• Read textbook sections on ATP, enzyme function, and regulation.
• Complete any assigned homework on metabolic pathways and energy transformations.