Chapter 6: Making Life Work - Cellular Metabolism and Enzymes

Vocabulary flashcards covering cellular requirements, metabolic classifications, thermodynamics, free energy, reaction types, and enzyme kinetics from Chapter 6.

Phototrophs

Organisms that capture their energy from sunlight.

Chemotrophs

Organisms that derive their energy from chemical compounds.

Autotrophs

Organisms that obtain carbon from inorganic sources, such as carbon dioxide ($\text{CO}_2$).

Heterotrophs

Organisms that obtain carbon from organic compounds.

Metabolism

The entirety of chemical reactions involving the building and breakdown of carbon sources to harness or release energy.

Anabolism

The set of metabolic reactions that build complex molecules from smaller units, requiring an input of energy ($\text{ATP}$).

Catabolism

The set of metabolic reactions that break down molecules into smaller units, producing energy ($\text{ATP}$).

Adenosine Triphosphate ($\text{ATP}$)

The primary energy currency of the cell, which stores potential energy in chemical bonds and releases energy when broken to fuel cellular reactions.

Potential Energy

Energy that is stored rather than associated with movement, such as the chemical energy held within molecular bonds.

Kinetic Energy

The form of energy associated with motion.

First Law of Thermodynamics

The physical law stating that energy cannot be created or destroyed, only transformed, meaning the total amount of energy remains constant.

Second Law of Thermodynamics

The physical law stating that energy transformations are not $100\%$ efficient, resulting in a decrease in energy available to do work and an increase in universal entropy.

Entropy ($S$)

The degree of disorder or randomness in a system, often increased by the release of energy in the form of heat during transformations.

Gibbs Free Energy ($G$)

The amount of energy in a system available to do work, related to enthalpy ($H$), temperature ($T$), and entropy ($S$) by the equation $\Delta G = \Delta H - T\Delta S$.

Endergonic Reaction

A nonspontaneous chemical reaction that requires a net input of free energy, characterized by a positive change in free energy ($+\Delta G$).

Exergonic Reaction

A spontaneous chemical reaction that releases energy, characterized by a negative change in free energy ($-\Delta G$).

Energetic Coupling

A thermodynamic mechanism in which a spontaneous reaction with a negative $\Delta G$ drives a nonspontaneous reaction with a positive $\Delta G$, resulting in an overall negative net $\Delta G$.

Activation Energy ($E_A$)

The initial input of energy required for a chemical reaction to reach the transition state and proceed.

Transition State

The intermediate, high-energy, unstable state during a chemical reaction that must be achieved for reactants to be converted into products.

Enzyme

A biological catalyst (typically a protein) that accelerates the rate of a chemical reaction by lowering the activation energy ($E_A$) without altering $\Delta G$.

Active Site

The specific region of an enzyme formed by folded amino acids where substrate molecules bind and catalysis takes place.

Enzyme-Substrate Complex ($ES$)

The temporary intermediate formed when an enzyme binds noncovalently to its specific substrate.

Competitive Inhibitor

A molecule that binds directly to an enzyme's active site, competing with the substrate and decreasing the reaction rate.

Noncompetitive Inhibitor

An inhibitor that binds to a site other than the active site, altering the enzyme's three-dimensional conformation and reducing the rate of reaction.

Negative Feedback

A regulatory mechanism in which the final product of a metabolic pathway inhibits an enzyme catalyzing an earlier step to conserve cellular resources.