Bioenergetics: Free Energy Changes (Vocabulary Flashcards)

Vocabulary flashcards covering key terms from the lecture notes on Gibbs free energy, equilibrium, ATP/ADP, cellular work, energy flow, and related calculations.

ΔG (Gibbs free energy change)

Change in Gibbs free energy for a reaction under given conditions; determines direction: ΔG < 0 means spontaneous forward progress, ΔG > 0 means non-spontaneous, ΔG = 0 at equilibrium.

ΔG°’ (standard biochemical free energy change)

Free energy change under biochemical standard conditions (25 °C, 1 atm, 1 M reactants, pH 7); constant for a given reaction and used to compare reactions.

Spontaneity (thermodynamic spontaneity)

A reaction is spontaneous under conditions when ΔG < 0; non-spontaneous when ΔG > 0.

Gibbs free energy

Energy capable of performing work in a system at constant temperature and pressure; drives whether reactions proceed.

Equilibrium

A state where forward and reverse reaction rates are equal, with no net change in reactant and product concentrations.

Equilibrium constant (Keq)

Ratio of product concentrations to reactant concentrations at equilibrium; related to ΔG°’ by ΔG°’ = -RT ln Keq.

Exergonic reaction

A reaction with negative ΔG°’; releases free energy and tends to proceed to completion; Keq > 1 under standard conditions.

Endergonic reaction

A reaction with positive ΔG°’; requires energy input and tends to have Keq < 1 under standard conditions.

ATP (adenosine triphosphate)

Cellular energy currency; hydrolysis to ADP + Pi releases energy to drive cellular work.

ADP (adenosine diphosphate)

Product of ATP hydrolysis; can be rephosphorylated to regenerate ATP.

Pi (inorganic phosphate)

Inorganic phosphate released or transferred during ATP hydrolysis and ATP synthesis.

Phosphoryl group transfer potential

Tendency of a molecule to donate a phosphate group; ATP has high transfer potential and readily donates phosphate.

Coupling (energy coupling)

Linking a thermodynamically unfavorable reaction with a highly favorable one (often ATP hydrolysis) so the overall ΔG is negative.

Hexokinase

Enzyme that catalyzes the phosphorylation of glucose to glucose-6-phosphate in glycolysis.

Glycolysis phosphorylation step (glucose to glucose-6-phosphate)

Thermodynamically unfavourable under standard conditions; becomes favorable when coupled to ATP hydrolysis.

Three basic cellular work types

Chemical work (biosynthesis), Transport work (membrane transport), Mechanical work (cell/organism movement).

Sunlight as energy source

Visible light energy captured by phototrophs and converted to chemical energy via photosynthesis.

Photosynthesis

Process by which light energy is converted to chemical energy stored in glucose; involves chlorophyll and pigments.

Chemolithoautotrophy

Organisms deriving energy by oxidizing inorganic compounds rather than from light.

Photolithoautotrophs

Organisms using light energy and inorganic carbon to synthesize organic molecules.

Cell energy currency cycle

Energy captured in ATP from energy-producing processes and used to perform work; ATP is regenerated from ADP and Pi.

ΔG = ΔG°’ + RT ln ([products]/[reactants])

Relation showing how actual free energy depends on standard free energy and current concentrations/temperature.

R (gas constant)

R = 8.3145 J·K⁻¹·mol⁻¹ (or 1.9872 cal·K⁻¹·mol⁻¹); used in thermodynamic calculations.

ΔG°’ for ATP hydrolysis

Standard free energy change for ATP hydrolysis is about -7.3 kcal/mol in biochemical contexts.

Calorie vs Joule

Calorie: amount of heat to raise 1 g of water by 1°C; 1 cal ≈ 4.184 J; Joule is the SI unit of work.

Phosphoryl group transfer potential (summary)

A measure of a molecule’s tendency to donate a phosphate group; ATP has a high potential and drives coupled reactions.