Metabolism, Thermodynamics, and Cellular Energy

Comprehensive vocabulary flashcards covering cellular metabolism, thermodynamic laws, free energy formulas, endergonic and exergonic reactions, enzymes, ATP energetics, and redox electron carriers.

Metabolism

All of the chemical reactions that take place within a cell, usually to transform matter and energy.

Metabolic pathways

Step-by-step sequences of reactions in cells where the product of one reaction serves as the reactant for the next, with each step catalyzed by a specific enzyme.

Anabolic reactions

Reactions that build complex molecules from simpler ones, requiring an input of energy.

Catabolic reactions

Reactions that break down large molecules into smaller products, releasing energy in the process.

Kinetic energy

The energy of motion.

Potential energy

Stored energy; free atoms possess more potential energy than the bonded compounds they form.

Bond energy

The energy involved in chemical bonds, where breaking a bond requires energy and forming a bond releases energy.

Thermodynamics

The study of energy changes within a system, which can be an entire organism or a specific collection of reactants and products.

Open systems

Systems that exchange both matter and energy with their surroundings, which characterizes all biological systems.

First Law of Thermodynamics

The principle stating that energy cannot be created or destroyed; it can only change form or be transferred between objects (also known as the Law of Conservation of Energy).

Second Law of Thermodynamics

The principle stating that the total entropy (disorder) of the universe increases during any energy transformation or process, with usable energy continuously converted into unusable heat energy.

Free energy ($G$)

The portion of energy from a chemical reaction that is available to perform work.

Enthalpy ($H$)

The total bond energy of a chemical system, denoted as change in enthalpy ($\Delta H$) in thermodynamic calculations.

Entropy ($S$)

A quantitative measure of disorder or randomness in a system, denoted as change in entropy ($\Delta S$).

Gibbs free energy equation

The formula used to calculate change in free energy: $\Delta G = \Delta H - T\Delta S$, where $T$ is temperature in Kelvin.

Endergonic reactions

Non-spontaneous chemical reactions with a positive free energy change ($\Delta G > 0$) where products contain more free energy than reactants, requiring an input of energy (e.g., photosynthesis).

Exergonic reactions

Spontaneous chemical reactions with a negative free energy change ($\Delta G < 0$) where products have less free energy than reactants, releasing energy as heat.

Activation energy

The initial push of energy required to destabilize existing chemical bonds and start a reaction.

Enzymes

Biological catalysts that speed up chemical reactions by lowering the activation energy without altering $\Delta G$ or being consumed by the reaction.

Adenosine triphosphate (ATP)

A cellular energy currency composed of an adenine base, a ribose sugar, and three phosphate groups, which stores usable energy in the unstable repulsive bonds between its negatively charged phosphate groups.

Hydrolysis of ATP

An exergonic reaction breaking down ATP with water: $\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i$, yielding $\Delta G = -30.6\,\text{kJ/mol}$.

Oxidation

The loss of electrons from a substance during a chemical reaction.

Reduction

The gain of electrons by a substance during a chemical reaction, which increases its energy level and reducing power.

Nicotinamide adenine dinucleotide

An electron carrier whose oxidized form is $\text{NAD}^+$ and reduced form is $\text{NADH}$.

Flavin adenine dinucleotide

An electron carrier whose oxidized form is $\text{FAD}$ and reduced form is $\text{FADH}_2$.