University:
The University Of Western Ontario
Course:
Biology 2290F | Scientific Method in Biology
Academic year:

2024
Views:

298

Pages:

2
Author:

Kyuwon J.

Bioenergetics • Application of thermodynamic principles to biological systems. • Describes energy flow and transformations. • Focuses on driving forces rather than molecular mechanisms. Primary Driving Forces in Biological Systems • Entropy (Free Energy, ∆G). • Mass Action Ratio. • Electrochemical/pH gradients. • Redox Potential. • Hydrophobic Force. • Temperature. Endergonic vs Exergonic Reactions • Energy consuming (Not Spontaneous). • Energy producing (Spontaneous). Laws of Thermodynamics • First Law: Energy is conserved. H = G + TS (1) • Second Law: The law of entropy. S = k log D (2) • Life is characterized by high order: S = k log(1/D), meaning life is negative entropy. Free Energy and Reaction Direction • ∆H = ∆G + T ∆S • ∆G = 0: Reaction at equilibrium. • ∆G > 0: Endergonic reaction. • ∆G < 0: Exergonic reaction. 1 Metabolic Control • Controlled by enzymes (rate) and regulation of substrate/product availability (direction). • Mass Action Ratio: ′ ∆G = ∆G◦ + RT ln [C][D] [A][B] (3) • At equilibrium, ∆G = 0, no net reaction: ′ ∆G◦ = −RT ln Keq (4) • Under physiological conditions: Q= [C]′ [D]′ [A]′ [B]′ (5) • Q > Keq , reverse reaction predominates. • Q < Keq , forward reaction predominates. ATP Hydrolysis Example ′ • ATP hydrolysis: ∆G◦ = −32.2 kJ/mol. • Mass Action Ratio: Q= [ADP ]′ [Pi ]′ ≈ 10−4 [AT P ]′ (6) • Q is 9 orders of magnitude lower than Keq , strongly favoring the forward reaction. Coupled Reactions • Exergonic ATP hydrolysis (−32.2 kJ/mol) drives less favorable reactions. • Example: Glucose phosphorylation. Glucose + Pi → Glucose-6-P, ′ ∆G◦ = +13.8 kJ/mol ◦′ ATP → ADP + Pi , ∆G = −32.2 kJ/mol Glucose + ATP → Glucose-6-P + ADP, 2 ′ ∆G◦ = −18.4 kJ/mol (7) (8) (9)