Energy, Thermodynamics, and Metabolic Regulation

Vocabulary flashcards covering energy forms, enthalpy, entropy, thermodynamic laws, catalytic mechanisms, metabolic pathways, redox reactions, and protein regulation.

Energy

The ability to promote change and do work, which determines the direction and rate of a chemical reaction.

Kinetic Energy

A form of energy that depends on movement and temperature.

Potential Energy

Stored or unstable energy that depends on location, position, or structure, such as the energy in chemical bonds.

Enthalpy ($H$)

The total energy of a system, measured in $J\,mol^{-1}$, defined mathematically by the relationship $H = G + TS$.

Free Energy ($G$)

The amount of a system's energy that is available and can be used to promote change and do work, measured in $J\,mol^{-1}$.

Unusable Energy ($TS$)

The portion of enthalpy that is tied up in disorder and locked in the random jiggling, spinning, and vibrating of atoms, which cannot be extracted to do useful work.

Entropy ($S$)

A measure of the degree of disorder of a system and how many microscopic arrangements are accessible, measured in $J\,mol^{-1}\,K^{-1}$; it is not itself energy, cannot be created or destroyed, but can be generated.

Second Law of Thermodynamics

The principle stating that when energy transfers from one form to another, entropy will always increase ($\Delta S > 0$), and the state of a natural system cannot be reversed without increasing the entropy of a system.

Exergonic Reaction

A spontaneous chemical reaction with a negative change in free energy ($\Delta G < 0$) that releases free energy as reactants move down to products.

Endergonic Reaction

A non-spontaneous chemical reaction with a positive change in free energy ($\Delta G > 0$) in which the reactants have lower free energy than the products, requiring an input of energy such as $ATP$.

Catalyst

An agent that speeds up the rate of a chemical reaction without being changed or consumed during the reaction, without altering $\Delta G$ or the direction of the reaction.

Riboenzymes

RNA molecules that function as biological catalysts to increase the rate of a chemical reaction.

Activation Energy ($E_A$)

The initial input of energy required in a chemical reaction that allows molecules to get close enough to cause a rearrangement of bonds.

Catabolic Reaction

A chemical reaction in a metabolic pathway where a molecule is broken down into smaller components, releasing energy (frequently $ATP$) and cleaning up or producing useful molecules.

Anabolic Reaction

A biosynthetic chemical reaction in a metabolic pathway that involves the synthesis of larger molecules from smaller molecules and requires an input of energy.

Feedback Inhibition

A biochemical regulation mechanism where a high concentration of the final product binds to an allosteric site on enzyme 1, causing a conformational change that inhibits its ability to convert the initial substrate and prevents overproduction.

Metabolic Pathways

A coordinated series of chemical reactions occurring in living cells in which each individual step is catalyzed by a specific type of enzyme.

Redox Reaction

A coupled chemical reaction in which an electron removed during the oxidation of an atom or molecule is transferred simultaneously to another atom or molecule that becomes reduced.

Oxidation

The process involving the loss of electrons from an atom or molecule, which may occur during the breakdown of small organic molecules.

Reduction

The process involving the gain of electrons by an atom or molecule, such as when $NAD^+$ is converted into $NADH$.

Genetic Regulation

A metabolic control mechanism that operates at the transcription level by switching genes on or off, such as through DNA methylation (adding a $-CH_3$ group).

Cellular Regulation

A level of metabolic regulation operating through cell signaling pathways, such as protein kinases and hormones, via modifications like phosphorylation (adding a phosphate group).

Ubiquitin

A small protein that attaches in strings to target proteins to track their age and target them for destruction.

Proteasome

A eukaryotic protein complex composed of four rings forming a core with caps that unfolds ubiquitinated proteins and degrades them into small peptides and amino acids.

Autophagosome

A self-eating organelle responsible for degrading cellular components, pathogens, bacteria, and viruses.