Overview
This lecture covers essential concepts and terminology about energy in biological systems, focusing on how cells use and manage energy for cellular respiration and photosynthesis.
When and Why Cells Need Energy
- Cells require energy for movement of materials within the cell and for whole cell movement.
- Cell division needs energy to create two new cells from one.
- Active transport of molecules (against a concentration gradient) across membranes uses energy.
- Some chemical reactions require energy input, while others release energy.
Types and Sources of Energy
- Potential energy is stored energy, found in covalent bonds and concentration gradients.
- Kinetic energy is energy in use, such as motion, light, and heat.
- Nonpolar covalent bonds contain more potential energy than polar covalent bonds.
- Lipids (fats) store more energy per gram than carbohydrates and proteins due to more nonpolar covalent bonds.
Chemical Reactions & Energy Changes
- Endergonic reactions require energy input; product bonds have more energy than reactants.
- Exergonic reactions release energy; reactant bonds have more energy than products.
- Exergonic and endergonic reactions are often coupled in cells to drive necessary processes.
Metabolism and Metabolic Pathways
- Metabolism is the sum of all chemical reactions in an organism.
- Metabolic pathways are multi-step sequences where the product of one reaction is the reactant of the next, each step requiring an enzyme.
Photosynthesis & Cellular Respiration
- Photosynthesis: Water + Carbon dioxide + Light energy → Sugar + Oxygen (endergonic, anabolic).
- Cellular respiration: Sugar + Oxygen → Carbon dioxide + Water (exergonic, catabolic).
Anabolic vs. Catabolic Reactions
- Anabolic reactions build complex molecules from simpler ones; require energy (endergonic).
- Catabolic reactions break down complex molecules into simpler parts; release energy (exergonic).
Laws of Thermodynamics
- First law: Energy is not created or destroyed, only changes form.
- Second law: Energy use increases disorder (entropy); heat is a highly disordered form of energy.
Redox (Oxidation-Reduction) Reactions
- Oxidation: loss of electrons (or hydrogen), Reduction: gain of electrons (or hydrogen).
- Redox reactions always occur together and are crucial in cellular respiration and photosynthesis.
ATP and Phosphorylation
- ATP (adenosine triphosphate) is the cell’s energy currency.
- Energy is released by breaking ATP’s phosphate bond (exergonic), driving other reactions (coupling).
- Regenerating ATP from ADP requires energy input (endergonic), which comes from food molecules or concentration gradients.
Key Terms & Definitions
- Potential Energy — Stored energy, often in chemical bonds or concentration gradients.
- Kinetic Energy — Energy of motion, such as heat or light.
- Endergonic Reaction — A reaction that absorbs energy.
- Exergonic Reaction — A reaction that releases energy.
- Metabolic Pathway — Series of chemical reactions where the product of one is the reactant of the next.
- Anabolic Reaction — Assembling complex molecules from simpler ones, energy required.
- Catabolic Reaction — Breaking down complex molecules into simpler ones, energy released.
- Entropy — Measure of disorder; increases as energy is used.
- Redox Reaction — Transfer of electrons; oxidation (loss) and reduction (gain).
- Phosphorylation — Addition of a phosphate group to a molecule, often transferring energy.
- ATP (Adenosine Triphosphate) — Main energy carrier in cells.
Action Items / Next Steps
- Review and memorize the equations for photosynthesis and cellular respiration.
- Learn the definitions of all key terms listed.
- Prepare for upcoming lectures on detailed mechanisms of cellular respiration and photosynthesis.