Overview
This lecture covered the origin, transformation, and use of energy in biological systems, focusing on laws of thermodynamics, types of energy, chemical reactions, ATP, and enzymes.
Energy and Life
- Energy is required for life and originates from the Sun, our local star.
- All living organisms rely on solar energy directly (autotrophs/plants) or indirectly (herbivores, carnivores).
- Energy transfer in ecosystems is not 100% efficient—some is always lost as heat.
Laws of Thermodynamics
- The First Law: Energy cannot be created or destroyed, only transformed (energy changes form).
- The Second Law: Every energy transformation increases disorder (entropy), and some energy is lost as heat.
Photosynthesis and Respiration
- Photosynthesis stores solar energy in glucose bonds within chloroplasts of plants.
- Photosynthesis occurs in two stages: capturing sunlight and using that energy to build glucose from CO₂.
- Aerobic respiration (in mitochondria) breaks down glucose with oxygen to release energy stored in ATP.
Forms of Energy
- Potential energy is stored energy (e.g., concentration gradients, chemical bonds like in glucose).
- Kinetic energy is energy of motion (e.g., muscle contraction, nerve signals).
- Chemical energy is a type of potential energy stored in atomic bonds.
Chemical Reactions
- Chemical reactions transform reactants into products, rearranging atoms without losing matter.
- Balanced chemical equations must have the same number of each atom on both sides.
- Photosynthesis is an endergonic reaction (energy in), aerobic respiration is exergonic (energy out).
- Endergonic: energy absorbed; exergonic: energy released.
ATP—The Energy Currency
- ATP (adenosine triphosphate) stores and transfers energy within cells.
- The energy is primarily in the bond between the second and third phosphate groups.
Enzymes and Catalysis
- Enzymes are proteins that act as catalysts, speeding up reactions by lowering activation energy.
- Enzymes are substrate-specific—only certain substrates fit their active sites.
- The induced fit model: enzyme adjusts shape when binding the substrate, facilitating the reaction.
- Enzyme names usually end in -ase and often indicate their substrate or function.
- Categories of enzymes: oxidoreductases, transferases, hydrolases, isomerases, ligases, lyases.
Enzyme Regulation
- Enzyme activity can be regulated by substrate concentration—more substrate increases reaction rate until saturation.
- Enzymes facilitate homeostasis by controlling reaction speed.
Key Terms & Definitions
- Autotroph — organism that makes its own food from sunlight or chemicals.
- ATP (Adenosine Triphosphate) — molecule that stores and transfers energy in cells.
- Chloroplast — organelle where photosynthesis occurs.
- Aerobic Respiration — process using oxygen to release energy from glucose.
- Potential Energy — stored energy due to position or structure.
- Kinetic Energy — energy of motion.
- Enzyme — protein that accelerates chemical reactions.
- Activation Energy — energy required to start a chemical reaction.
- Active Site — region on an enzyme where the substrate binds.
- Substrate — reactant on which an enzyme acts.
- Homeostasis — maintenance of stable internal conditions in an organism.
Action Items / Next Steps
- Review the six main categories of enzymes and their functions.
- Understand and memorize the basic formula for photosynthesis and respiration.
- Prepare questions on enzyme regulation for next class.