Chemical Concepts and Bioenergetics

These vocabulary flashcards cover the fundamental thermodynamic and kinetic concepts of bioenergetics, including Gibbs free energy, ATP functionality, and reaction rates.

Bioenergetics

The study of the transfer and utilization of energy in biologic systems.

Gibbs free energy ($G$)

A description of the potential energy of a chemical reaction or system with the capacity to do work, named after J. Willard Gibbs.

$$\Delta G$$

The change in free energy that determines whether a reaction will proceed spontaneously in the forward or reverse direction.

Equilibrium constant ($K$ or $K_{eq}$)

The ratio of the concentration of products to the concentration of reactants in a chemical system.

Standard free energy change ($\Delta G^{o'}$)

A reference value representing the change in free energy when going from reactants and products at $1\,M$ to their equilibrium values at $pH = 7$ ($[H^+] = 1 \times 10^{-7}\,M$).

Gas constant ($R$)

A constant used in the calculation of free energy, valued at $1.987\,cal/mol \cdot K$.

Thermodynamic coupling

The process by which a thermodynamically unfavorable reaction is driven by a thermodynamically favorable one if the reactions are linked by a common intermediate.

High-energy bonds

Bonds in which free energy is released upon hydrolysis, such as the phosphoanhydride bonds in ATP.

ATP (Adenosine Triphosphate)

The primary energy "currency" of the cell, often used to drive thermodynamically unfavorable reactions.

Charge repulsion

One of the reasons ATP hydrolysis is favorable; it occurs because several negatively charged oxygens are in close proximity in the phosphoanhydride bonds of ATP and are partially relieved in the product ADP.

Resonance stabilization

A factor contributing to the energy difference in ATP hydrolysis, specifically referring to the stability of the inorganic phosphate released during the reaction.

Activation energy ($E_a$ or $\Delta G^{\ddagger}$)

The energy required to excite molecules into a transition state to progress and form the products of a reaction; it is a major determinant of the reaction rate.

Transition state ($T^*$)

The highest energy and least stable form of the reactant during a chemical reaction.

Progress of reaction curve

A plot showing free energy for reactants and products on the Y-axis versus the hypothetical transition from reactants to products on the X-axis.

Enzymes

Biological catalysts, typically proteins, that increase the rate of a reaction by decreasing the activation energy ($E_a$).

Exergonic reaction

A reaction that releases energy and is characterized by a negative $\Delta G$.

Endergonic reaction

A reaction that requires an input of energy and is characterized by a positive $\Delta G$.