Overview
This lecture covers the types of energy relevant to biology: potential, kinetic, free, and activation energy, including how these concepts relate to chemical reactions in living systems.
Types of Energy
- Energy is defined as the ability to do work.
- Kinetic energy is the energy of motion, present in moving objects.
- Potential energy is stored energy due to an object's position or structure.
- Chemical energy is a form of potential energy stored within chemical bonds in molecules.
Kinetic vs. Potential Energy
- Moving objects, like falling water or running cars, possess kinetic energy.
- Objects at rest in a position to move, such as water behind a dam, have potential energy.
- Potential energy can be converted to kinetic energy and vice versa.
Chemical Energy and Biological Systems
- Chemical bonds in food molecules store potential energy.
- Breaking these bonds releases energy that living cells use to perform work.
- Anabolic pathways build complex molecules and require energy (endergonic), while catabolic pathways break down molecules and release energy (exergonic).
Free Energy (Gibbs Free Energy)
- Free energy (G) measures the usable energy available to do work after accounting for entropy.
- The change in free energy (ΔG) in a reaction indicates its spontaneity.
- ΔG = ΔH – TΔS, where ΔH is enthalpy, T is temperature in Kelvin, and ΔS is entropy.
Endergonic and Exergonic Reactions
- Exergonic reactions release energy, have a negative ΔG, and occur spontaneously.
- Endergonic reactions require energy input, have a positive ΔG, and are non-spontaneous.
- Anabolic processes are usually endergonic; catabolic processes are usually exergonic.
Chemical Equilibrium in Cells
- Chemical reactions are reversible and move towards equilibrium.
- Living cells are open systems and maintain reactions away from equilibrium to stay alive.
- Continuous energy input is needed to prevent equilibrium and sustain life.
Activation Energy
- All chemical reactions require some initial energy input, called activation energy (EA), to proceed.
- Activation energy is needed to reach a high-energy, unstable transition state before new bonds form or break.
- Heat energy usually provides activation energy, but catalysis (by enzymes) lowers EA in cells.
- Lower activation energy means faster reaction rates; high activation energy makes reactions slow.
Key Terms & Definitions
- Kinetic energy — energy due to motion.
- Potential energy — stored energy based on position or structure.
- Chemical energy — potential energy stored within chemical bonds.
- Free energy (G) — usable energy available to do work in a system.
- Enthalpy (H) — total energy in a system.
- Entropy (S) — measure of disorder or unusable energy.
- Exergonic reaction — releases energy; negative ΔG; spontaneous.
- Endergonic reaction — requires energy; positive ΔG; non-spontaneous.
- Activation energy (EA) — the initial energy needed to start a reaction.
- Transition state — high-energy, unstable state during a reaction.
Action Items / Next Steps
- Review examples of kinetic and potential energy in everyday life.
- Practice calculating ΔG using the Gibbs free energy equation.
- Complete any assigned questions on endergonic vs. exergonic reactions and activation energy.