Thermodynamics and Biochemical Pathways

These flashcards cover key concepts and terms in thermodynamics and its application in metabolic pathways.

First Law of Thermodynamics

Energy cannot be created or destroyed, only transformed.

ΔE

Change in internal energy, calculated as ΔE = q + w.

Heat (q)

Energy flow from surroundings to a system, considered positive when transferred to the system.

Work (w)

Energy transferred as a result of a force moving an object, considered positive when transferred to the system.

Enthalpy (ΔH)

The heat content of a system at constant pressure, indicating whether a reaction is exothermic (ΔH < 0) or endothermic (ΔH > 0).

Exothermic

A chemical reaction that releases heat, leading to a negative change in enthalpy (ΔH < 0).

Endothermic

A chemical reaction that absorbs heat, resulting in a positive change in enthalpy (ΔH > 0).

Entropy (S)

A measure of disorder or randomness in a system; the total entropy change in the universe for any process is greater than zero.

Second Law of Thermodynamics

The total entropy of an isolated system can never decrease over time and will increase until reaching equilibrium.

Gibbs Free Energy (ΔG)

A thermodynamic potential that can be used to predict the direction of a reaction; calculated as ΔG = ΔH - TΔS.

Exergonic Reaction

A reaction with a negative Gibbs Free Energy (ΔG < 0) that proceeds spontaneously.

Endergonic Reaction

A reaction with a positive Gibbs Free Energy (ΔG > 0) that is non-spontaneous.

Standard Conditions

Specific conditions set at 0°C (273 K) and 1 atm for comparing laboratory measurements.

Near Equilibrium Reactions

Reactions where ∆G is approximately zero, sensitive to substrate or product concentration changes.

Metabolically Irreversible Reactions

Reactions with a significantly negative ∆G that cannot proceed in reverse.

ATP (Adenosine triphosphate)

The central energy intermediate in cellular metabolism, driving numerous biochemical reactions.

Energy Coupling

The linking of an endergonic process to an exergonic process to drive a combined favorable reaction.

NADH

The principal electron carrier in cellular metabolism, essential for redox reactions.

Oxidation

The process of losing electrons during a chemical reaction.

Reduction

The process of gaining electrons during a chemical reaction.

Creatine Phosphokinase

An enzyme that catalyzes the conversion of creatine and ATP to creatine phosphate and ADP.

NDP Kinase

An enzyme that facilitates the transfer of phosphate between nucleotides, maintaining ATP levels.

Adenylate Kinase

An enzyme that catalyzes the reaction of ATP and AMP to form two ADP molecules, maintaining energy balance.

Mobile Cofactors

Energy intermediates such as ATP, ADP, NADH, and others that connect various metabolic pathways.

Prosthetic Groups

Cofactors that are permanently attached to enzymes, essential for their activity.

Hydride Ion Transfer

The transfer of a hydrogen atom with two electrons to another molecule, primarily seen in redox reactions.

Standard Free Energies of Hydrolysis

The energy change associated with the hydrolysis of ATP and related nucleotides.

Pathway View

An approach to visualize connections between metabolic reactions, where products of one reaction serve as substrates of another.

Chelation with Mg2+

The process of binding magnesium ions to stabilize ATP, essential for its function in biochemical reactions.