Energy Forms and Thermodynamics

Forms of Energy

• Kinetic energy is the energy of motion.
• Potential energy is stored energy due to an object's position or structure.
• Thermodynamics is the study of energy transformations.

The Laws of Thermodynamics

• First Law: Energy cannot be created or destroyed, only converted from one form to another.
• Second Law: The entropy (disorder) of the universe always increases.

Gibbs Free Energy

• Gibbs Free Energy (G) is the portion of a system's energy available to do work.
• A negative Gibbs Free Energy value indicates a spontaneous reaction (energy releasing).
• Exergonic reactions release energy (e.g., cellular respiration).
• Endergonic reactions require energy (e.g., photosynthesis).

Energy Coupling

• ATP (adenosine triphosphate) is the primary energy currency of cells.
• ATP hydrolysis releases energy and is coupled with endergonic reactions.
• ATP hydrolysis equation: ATP + H₂O → ADP + Pi + energy

Types of Cellular Work

• Chemical work: synthesis of molecules
• Transport work: moving molecules across membranes
• Mechanical work: movement of cells or cellular structures

Role of Enzymes in Chemical Reactions

• Enzymes are biological catalysts that speed up reactions by lowering activation energy.
• Activation energy is the minimum energy required for a reaction to occur.

Factors Affecting Enzyme Activity

• Cofactors: non-protein molecules that assist enzyme function (e.g., calcium, iron).
• pH: changes in pH can alter an enzyme's shape and function.
• Temperature: extreme temperatures can denature enzymes.
• Inhibitors: molecules that block enzyme activity.
  • Competitive inhibitors bind to the active site.
  • Non-competitive inhibitors bind to a different site, changing the enzyme's shape.
• Feedback inhibition: excess product can act as an inhibitor to regulate enzyme activity.

Cellular Respiration

• Cellular respiration is the process of breaking down glucose to generate ATP, CO₂, water, and heat.
• Redox reactions involve the transfer of electrons.
  • Oxidation is the loss of electrons.
  • Reduction is the gain of electrons.
• Glucose + 6O₂ → 6CO₂ + 6H₂O + ATP + Heat
• Electron Transport Chain is located in the cristae of mitochondria.
• Oxygen is the final electron acceptor in cellular respiration.

Stages of Cellular Respiration

• Glycolysis: occurs in the cytoplasm.
  • Energy investment phase uses 2 ATP.
  • Energy payoff phase produces 4 ATP, 2 NADH, and 2 pyruvate.
• Preparation Step: oxidizes pyruvate to acetyl-CoA, generates CO₂, and produces NADH.
• Citric Acid Cycle: occurs in the mitochondrial matrix.
  • Produces 2 ATP, 4 CO₂, 6 NADH, and 2 FADH₂.
• Oxidative Phosphorylation: occurs in the inner mitochondrial membrane.
  • Electron transport chain uses NADH and FADH₂ to generate a proton gradient.
  • ATP synthase uses the proton gradient to produce ATP.

Breathing and Cellular Respiration

• Breathing is the exchange of gases (oxygen in, CO₂ out).
• Cellular respiration uses oxygen as the final electron acceptor and produces CO₂.

Substrate Level Phosphorylation vs. Oxidative Phosphorylation

• Substrate level phosphorylation: an enzyme directly transfers a phosphate group from a substrate to ADP to produce ATP.
• Oxidative phosphorylation: the electron transport chain generates a proton gradient that drives ATP synthesis.