Energetics of Living Systems

Vocabulary practice flashcards covering thermodynamics, free energy calculations, enzyme catalysis, regulation, and ATP energetics from Biology 1105.

Energy

The capacity to do work.

Kinetic energy

The energy of motion.

Oxidation

The loss of an electron from a chemical substance, resulting in a lower level of energy.

Reduction

The gain of an electron by a chemical substance, resulting in a higher level of energy.

Oxidation-reduction (redox) reactions

Paired chemical reactions involving the breaking and forming of chemical bonds through the transfer of electrons from one substance to another.

First Law of Thermodynamics

The principle stating that energy cannot be created or destroyed, though some is lost as heat during energy conversion, resulting in a continuous flow of energy through the biological world from the Sun to heat.

Second Law of Thermodynamics

The principle stating that entropy (disorder) is continuously increasing, causing energy transformations to proceed spontaneously to convert matter from a more ordered / less stable form to a less ordered / more stable form.

Entropy ($S$)

A measure of the disorder in a system that is continuously increasing in the universe.

Gibbs free energy ($G$)

The energy available to do work in a system, defined by the equation $G = H - TS$, where $H$ is enthalpy, $T$ is absolute temperature ($^\circ\text{C} + 273$), and $S$ is entropy.

Endergonic reaction

A non-spontaneous chemical reaction requiring supplied energy, characterized by a positive change in free energy ($\Delta G > 0$) where the products have more free energy than the reactants.

Exergonic reaction

A spontaneous chemical reaction that releases energy, characterized by a negative change in free energy ($\Delta G < 0$) where the products have less free energy than the reactants.

Activation energy

The extra energy required to destabilize existing chemical bonds and initiate a chemical reaction.

Catalyst

A substance that lowers the activation energy of a reaction without violating thermodynamic laws or changing the final proportion of reactant converted to product.

Enzyme

A biological catalyst—typically a protein, though some are RNA molecules—whose specific shape stabilizes transient associations between substrates.

Active site

A pocket or cleft on an enzyme where a substrate binds and experiences bond-distorting stress that lowers activation energy.

Induced fit

The conformational shape change an enzyme undergoes upon substrate binding to maximize contact and catalyze the reaction.

Competitive inhibitor

An inhibitor molecule that binds directly to the active site of an enzyme, competing with the substrate to prevent reaction occurrence.

Non-competitive inhibitor

An inhibitor molecule that binds to an enzyme at an allosteric site rather than the active site, causing a conformational change that prevents substrate binding.

Allosteric site

A specific location on an enzyme distinct from the active site where regulatory molecules bind to influence enzyme activity.

Metabolism

The total of all chemical reactions carried out by an organism.

Catabolism

Metabolic reactions that harvest energy through the breakdown of larger molecules.

Biochemical pathway

A sequential series of chemical reactions in which the product of one reaction serves as the substrate for the subsequent reaction.

Feedback inhibition

A regulatory mechanism in which the end-product of a biochemical pathway binds to the allosteric site of the first enzyme, shutting down the pathway to prevent wasting energy and materials.

Adenosine triphosphate (ATP)

The cellular source of chemical potential energy containing high-energy bonds between phosphate groups whose hydrolysis drives endergonic reactions.

ATP cycle

The cyclic coupling of ATP hydrolysis (releasing energy to drive endergonic cellular processes and yielding ADP and $\text{P}_i$) with ATP synthesis (powered by exergonic cellular reactions).

Phosphorylation / dephosphorylation

A molecular light switch mechanism controlling protein activity in which kinases add a phosphate group and phosphatases remove a phosphate group.