Biochemistry and Thermodynamics

Introduction to Biochemistry

• Biochemistry is the study of the chemistry of life, overlapping with cell biology, genetics, and physiology.

• It addresses: chemical/3D structures of biomolecules, their interactions, synthesis/degradation, energy conservation/use, organization/coordination, and genetic information storage/transmission/expression.

Living Systems

• Composition: Primarily H, O, N, C (constitute >99% of atoms in human body).

• Carbon's versatility allows for complex 3D structures.

• Characteristics: Complicated, highly organized, require functional biological structures, engage in energy transformations, have self-replication capacity.

• Functional groups are crucial for understanding biomolecule structural interactions (e.g., ATP, DNA, amino acids).

Thermodynamics Fundamentals

• Definition: The study of energy and its effects on matter.

• First Law: Energy is conserved; it is neither created nor destroyed, only converted from one form to another. For any process, the total energy ($E$) of a system and its surroundings is constant ($\Delta E = q + w$).

• Enthalpy (H): Reflects the heat absorbed or evolved ($\Delta H$) at constant pressure, representing bond-making or breaking.

  • Exothermic: \Delta H < 0 (heat evolved, more stable bonds).

  • Endothermic: \Delta H > 0 (heat absorbed, less stable bonds).

• Second Law: The disorder ($S$) of the universe constantly increases. Spontaneous processes are characterized by the conversion of order to disorder.

• Entropy (S): A measure of randomness or disorder.

  • \Delta S < 0: Final state is more ordered.

  • \Delta S > 0: Final state is less ordered.

Spontaneity of Reactions and Life

• Free Energy (G): Describes the relationship between enthalpy, entropy, and temperature (T).

  • Gibbs free energy change ($\Delta G$) determines spontaneity: $\Delta G = \Delta H - T\Delta S$.

• Spontaneous Process (Exergonic): Occurs without outside intervention, with a decrease in free energy (\Delta G < 0).

• Non-Spontaneous Process (Endergonic): Requires outside intervention, with an increase in free energy (\Delta G > 0).

• Equilibrium: $\Delta G = 0$, no net change.

• Life and Thermodynamics: Organisms are nonequilibrium, open systems that constantly exchange matter and energy with surroundings, maintaining a steady state and obeying the laws of thermodynamics.

• Enzymes increase the rates of thermodynamically favorable reactions, but do not change their spontaneity ($\Delta G$).