Overview
This lecture covers the core concepts of metabolism, focusing on energy transformation, thermodynamics, ATP, enzyme function, and metabolic regulation as explained in Campbell Biology Chapter 8.
Metabolism and Metabolic Pathways
- Metabolism refers to all chemical reactions in an organism.
- A metabolic pathway alters a molecule in a series of enzyme-catalyzed steps to form a final product.
- Catabolic pathways break down complex molecules, releasing energy (e.g., cellular respiration).
- Anabolic pathways build complex molecules, consuming energy (e.g., protein synthesis).
Forms of Energy
- Energy is the capacity to cause change or do work.
- Kinetic energy is energy of motion; thermal energy is kinetic energy of molecular movement.
- Heat is thermal energy transferred between objects.
- Potential energy is stored due to location or structure (e.g., water behind a dam, a drawn bow).
- Chemical energy is potential energy stored in molecular bonds (e.g., glucose).
Energy Transformation and Thermodynamics
- Living organisms transform energy from one form to another.
- Thermodynamics is the study of energy transformations.
- Organisms are open systems, exchanging energy and matter with their environment.
- The first law (conservation of energy): energy cannot be created or destroyed, only transformed.
- The second law: every transformation increases the universe's entropy (disorder).
- Entropy refers to molecular disorder; breaking down molecules or diffusion increases entropy.
Free Energy and Spontaneity
- Free energy (G) is the portion of a system's energy that can do work at uniform temperature and pressure.
- Processes with negative ΔG are spontaneous (energetically favorable); those with positive ΔG are non-spontaneous (require energy input).
- At equilibrium, ΔG = 0; the system is stable and does no work.
- The Gibbs free energy equation: ΔG = ΔH – TΔS (ΔH = enthalpy change, ΔS = entropy change, T = temperature in Kelvin).
Exergonic and Endergonic Reactions
- Exergonic (exergonic) reactions have negative ΔG, release energy, and are spontaneous.
- Endergonic reactions have positive ΔG, absorb energy, and are non-spontaneous.
- Cells couple exergonic reactions (e.g., ATP hydrolysis) to drive endergonic processes.
ATP: Structure and Function
- ATP (adenosine triphosphate) consists of adenine, ribose, and three phosphate groups.
- The high energy comes from repulsion among negatively charged phosphate groups.
- Hydrolysis of ATP releases energy by removing a terminal phosphate, forming ADP and Pi (inorganic phosphate).
- ATP powers work by coupling energy-releasing reactions to energy-consuming ones.
Enzymes and Catalysis
- Enzymes are protein catalysts that lower activation energy and speed up reactions.
- Enzyme specificity depends on the shape of the active site and substrate (“induced fit”).
- Enzyme activity is affected by temperature and pH, with each enzyme having optimal conditions.
- Some enzymes require nonprotein cofactors (minerals) or coenzymes (vitamins) to function.
- Inhibitors can decrease enzyme activity: competitive inhibitors block the active site; non-competitive inhibitors bind elsewhere and alter the enzyme's shape (allosteric regulation).
Regulation of Metabolic Pathways
- Allosteric regulation involves molecules binding to an enzyme at one site, altering activity at the active site.
- Feedback inhibition occurs when a pathway’s end product inhibits an early enzyme, preventing overproduction and conserving resources.
Key Terms & Definitions
- Metabolism — sum of all chemical reactions in an organism.
- Catabolism — breakdown of complex molecules, releasing energy.
- Anabolism — synthesis of complex molecules, consuming energy.
- Kinetic energy — energy of motion.
- Potential energy — stored energy due to position or structure.
- Entropy — measure of disorder/randomness.
- Free energy (G) — system energy available to do work.
- Exergonic reaction — reaction that releases energy (negative ΔG).
- Endergonic reaction — reaction that absorbs energy (positive ΔG).
- Enzyme — protein catalyst that speeds up reactions.
- Activation energy (EA) — energy required to start a reaction.
- Cofactor — nonprotein enzyme helper (e.g., minerals).
- Coenzyme — organic cofactor (e.g., vitamins).
- Competitive inhibitor — molecule that competes for the active site.
- Non-competitive inhibitor — molecule that binds elsewhere, affecting enzyme function.
- Allosteric regulation — regulation via molecule binding at a site other than the active site.
- Feedback inhibition — pathway end product inhibits an early enzyme.
Action Items / Next Steps
- Review and memorize key terms and definitions.
- Practice applying the Gibbs free energy equation to reaction scenarios.
- Complete textbook readings on enzyme structure and function.
- Prepare for next chapter: cellular respiration.