Energy, Cell Metabolism, Enzymes, and Glucose Catabolism

Matter

Material that takes up space and has mass or weight, including atoms, molecules, macromolecules, and cells.

Energy

The capacity to do work, cause change, move matter, or change the arrangement of matter.

Potential Energy

Stored energy derived from an object's position, location, or the arrangement of its parts.

Kinetic Energy

The energy of motion, which includes thermal energy (random movement of atoms and molecules) and particles or ions moving down a concentration gradient.

Chemical Energy

A form of potential energy stored within chemical bonds due to the arrangement of atoms, available for release during chemical reactions.

First Law of Thermodynamics

The law of energy conservation stating that energy in the universe is constant; it can be transferred and transformed, but cannot be created or destroyed.

Second Law of Thermodynamics

The principle stating that every energy transfer or transformation results in an increase in the entropy (disorder) of the universe, with useful energy declining spontaneously as some energy is lost as heat.

Entropy

A measure of disorder or randomness in a system that increases spontaneously throughout the universe.

Exergonic Reaction

A spontaneous chemical reaction ($\Delta G < 0$) that releases energy, in which the reactants possess more potential energy than the products.

Endergonic Reaction

A non-spontaneous chemical reaction ($\Delta G > 0$) that requires an input of energy from the cell, yielding products that possess more potential energy than the reactants.

Catabolism

Metabolic degradation pathways that break down complex molecules into simpler compounds, releasing energy for cellular work (exergonic).

Anabolism

Metabolic synthesis pathways that build larger, complex molecules from simpler precursors, requiring an input of energy (endergonic).

Metabolism

The sum total of all chemical reactions (both catabolic and anabolic) occurring within a cell or organism.

Activation Energy ($E_a$)

The minimum amount of energy required to contort reactant chemical bonds and initiate a chemical reaction.

Transition State

The high-energy, unstable intermediate state in a chemical reaction at which reactant bonds are broken and product bonds begin to form.

Catalyst

A substance that accelerates the rate of a chemical reaction without being consumed or produced by positioning reactants so they react more easily.

Enzyme

A specialized catalytic protein with a specific three-dimensional conformation that accelerates biochemical reactions by lowering activation energy ($E_a$).

Active Site

The specific region within an enzyme's tertiary structure where a substrate binds and catalysis takes place.

Substrate

The specific reactant molecule that binds to an enzyme's active site and is chemically converted into a product.

Induced Fit

The slight conformational change in an enzyme's active site upon substrate entry that binds the substrate snugly and strains its chemical bonds.

Catalytic Cycle

A multistep reaction mechanism in which an enzyme binds a substrate, converts it to products, releases the products, and returns to its original shape for reuse.

Denaturation

The permanent loss of an enzyme's native three-dimensional shape and biological activity, typically caused by temperatures above $50\,^{\circ}\text{C}$ or non-optimal $\text{pH}$.

Competitive Inhibitor

A regulatory substance that reduces an enzyme's activity by mimicking the substrate structure and physically blocking the active site.

Noncompetitive Inhibitor

A regulatory substance that reduces enzyme activity by binding to an allosteric site rather than the active site