Lesson 07: Energetics of Living Systems

Energy

The capacity to do work or cause change; essential for biological processes.

Potential Energy

Stored energy due to position or structure, such as energy in chemical bonds.

Kinetic Energy

Energy of motion; used when molecules move or enzymes catalyze reactions.

Redox Reaction

A chemical reaction involving the transfer of electrons; includes oxidation (loss) and reduction (gain).

1st Law of Thermodynamics

Energy cannot be created or destroyed, only transformed or transferred.

2nd Law of Thermodynamics

Every energy transfer increases the disorder (entropy) of the universe.

Free Energy (G)

The energy available to do work in a system; determines reaction spontaneity.

Enthalpy

Total heat content of a system; reflects energy stored in chemical bonds.

Entropy

Measure of disorder or randomness in a system; increases in spontaneous processes.

Endergonic

A reaction that absorbs energy; non-spontaneous (ΔG > 0).

Exergonic 

A reaction that releases energy; spontaneous (ΔG < 0).

Activation Energy

The energy required to start a chemical reaction.

Catalyst

A substance that speeds up a reaction without being consumed.

Enzyme

A biological catalyst, usually a protein, that speeds up specific reactions.

Active Site

The region on an enzyme where the substrate binds and the reaction occurs.

Enzyme-Substrate Complex

Temporary structure formed when an enzyme binds its substrate.

Competitive Inhibition 

Inhibitor competes with substrate for the active site, blocking enzyme activity.

Noncompetitive Inhibition

Inhibitor binds elsewhere on the enzyme, changing its shape and reducing activity.

Allosteric Site

A site on an enzyme where a molecule can bind and regulate activity, not the active site.

Substrate

The reactant that an enzyme acts upon.

Metabolism

All chemical reactions in a cell, including energy production and molecule synthesis.

Anabolism

Metabolic pathways that build complex molecules from simpler ones; requires energy.

Catabolism

Metabolic pathways that break down molecules into simpler ones; releases energy.

Biochemical Pathway

A series of linked chemical reactions in a cell, often enzyme-catalyzed.

Feedback Inhibition

A process where the end product of a pathway inhibits an earlier step to regulate activity.

ATP

Main energy currency of the cell; stores and transfers energy for cellular work.

Coupled Reaction

Two reactions linked together; one releases energy to drive the other.

Kinase

An enzyme that adds a phosphate group to a molecule, often regulating activity.

Phosphatase

An enzyme that removes a phosphate group from a molecule.