Study Notes for Chapter 3: Bioenergetics, Enzymes and Metabolism

Chapter 3: Bioenergetics, Enzymes and Metabolism

3.0 You Are Not What You Eat

  • Humans use food for energy that powers movement, metabolism, and thought.

  • Biochemical reactions convert nutrients into ATP (Adenosine triphosphate).

  • Enzymes facilitate these reactions to produce ATP and cellular building blocks.

3.1 The Law of Thermodynamics

  • Cells acquire and expend energy to maintain activity conditions.

  • Bioenergetics studies energy transformation in living organisms.

  • Energy definition: capacity to do work; Thermodynamics studies energy change.

First Law of Thermodynamics

  • Conservation of energy: Energy can be converted but not created or destroyed.

  • Cells are capable of energy transduction, storage, and transport.

  • Chemical energy in biological molecules like ATP.

  • Key process: Photosynthesis converts sunlight to chemical energy.

Change in Energy (ΔE)

  • Defined as ΔE = Q - W, where E is internal energy, Q is heat, W is work.

  • Exothermic reactions release heat; endothermic reactions absorb heat.

3.2 The Second Law of Thermodynamics

  • Events favor transition from high to low energy states, termed spontaneous.

  • Entropy measures randomness; every process increases total entropy.

Living Systems

  • Maintain order by increasing environmental entropy (heat energy).

  • Relationship: Loss of available energy equals TΔS.

3.3 Spontaneity and Free Energy

  • Free Energy equation: ΔG = ΔH – TΔS assesses process spontaneity.

  • ΔG negative: spontaneous; ΔG positive: non-spontaneous.

  • Chemical reactions shift towards equilibrium, defined by the equilibrium constant (Keq).

ATP Hydrolysis

  • Standard free energy of ATP hydrolysis: ΔGo' = -7.3 kcal/mol indicates spontaneity.

  • ATP hydrolysis drives endergonic processes in cells.

3.4 Enzymes

  • Enzymes as catalysts speed up reactions significantly.

  • Properties: Specificity, regulation, not permanently altered, and increase reaction rates by lowering activation energy.

3.5 Enzyme Kinetics

  • Rates increase with substrate concentration until saturation (Vmax).

  • Michaelis constant (KM): Substrate concentration at half Vmax; indicates enzyme affinity.

3.6 Inhibition

  • Enzyme inhibitors slow reactions; types include competitive (substance mimics substrate) and noncompetitive (inhibitor binds other site).

  • Maximal velocity is impacted by noncompetitive inhibitors.