Chapter 6: Energy and Metabolism Flashcards

Comprehensive vocabulary flashcards covering basic thermodynamics, free energy equations, enzyme structure/function, activation energy, ATP dynamics, and metabolic regulation from Chapter 6.

Energy

The capacity to do work, which exists in potential and kinetic states.

Potential Energy

Stored energy, such as chemical energy stored in the covalent bonds of molecules.

Kinetic Energy

The energy of motion.

Heat

A measure of the random movement of molecules; the most convenient form of energy to measure.

Kilocalorie (kcal)

A unit equal to $1000\text{ calories}$ (or $1\text{ Calorie}$ on food labels), where $1\text{ calorie}$ is the heat needed to raise $1\,g$ of water by $1^\circ\text{C}$.

Oxidation

A chemical reaction in which an atom or molecule loses an electron.

Reduction

A chemical reaction in which an atom or molecule gains an electron.

Redox Reactions

Paired oxidation-reduction reactions key to energy flow in biological systems, where an electron lost by one atom is picked up by another.

First Law of Thermodynamics

The principle that energy cannot be created or destroyed, but can only change from one form to another.

Second Law of Thermodynamics

The principle stating that energy conversions are not completely efficient and that energy is lost as disorder increases.

Entropy

The amount of disorder in a system.

Free Energy

The energy available to break and reform chemical bonds and do work in a system, expressed as $\Delta G = \Delta H - T\Delta S$.

Enthalpy (H)

The energy contained in the chemical bonds of a molecule or system.

Endergonic Reaction

A nonspontaneous reaction requiring an input of energy, in which the products contain more free energy than the reactants ($\Delta G > 0$).

Exergonic Reaction

A spontaneous reaction that releases free energy, in which the products contain less free energy than the reactants ($\Delta G < 0$).

Activation Energy

The extra energy required to destabilize existing chemical bonds and initiate a chemical reaction.

Catalysis

The process of stressing chemical bonds to lower activation energy, accelerating both forward and reverse reactions without altering the change in free energy.

Adenosine Triphosphate (ATP)

A nucleotide composed of ribose, adenine, and three strongly repulsive phosphate groups that acts as the cell's energy currency.

ATP-ADP Cycle

The cyclical system in which ATP is synthesized from ADP and $P_i$ using exergonic energy, and hydrolyzed to provide energy for endergonic cellular processes.

Substrate

A specific reactant molecule that binds to an enzyme to undergo a chemical reaction.

Active Site

A cleft or pocket on the surface of an enzyme where substrate binding and catalysis take place.

Enzyme-Substrate Complex

The complex formed when a substrate molecule binds to the active site of an enzyme.

Induced Fit

The slight conformational change in an enzyme caused by substrate binding that facilitates catalysis or the binding of additional substrates.

Multienzyme Complex

An assembly of several enzymes that catalyze sequential steps in a metabolic pathway.

Ribozymes

Nonprotein RNA molecules capable of intramolecular or intermolecular catalysis.

Optimum Temperature

The temperature at which an enzyme functions most efficiently, corresponding to $35\text{--}40^\circ\text{C}$ for most human enzymes.

Optimum pH

The pH range at which ionic interactions maintain optimal enzyme structure and activity, typically pH $6\text{--}8$ for most human enzymes.

Competitive Inhibitors

Regulatory molecules that decrease enzyme activity by competing directly with the substrate for binding at the active site.

Allosteric Site

A specific regulatory site on an enzyme distinct from the active site, serving as a chemical on/off switch when bound by inhibitors or activators.

Cofactors

Additional nonprotein chemical components, such as inorganic metal ions (zinc, molybdenum, manganese), that assist enzyme function.

Coenzymes

Nonprotein organic cofactor molecules, such as vitamins B6 and B12, that aid enzyme function.

Metabolism

The sum total of all chemical reactions carried out by an organism.

Anabolism

Metabolic reactions that expend energy to build complex molecules from simpler ones.

Catabolism

Metabolic reactions that harvest energy by breaking down complex molecules.

Biochemical Pathways

Sequential enzymatic reactions serving as organizational units of metabolism, where the product of one step becomes the substrate for the next.

Feedback Inhibition

A control mechanism in which the final end-product of a pathway binds to the allosteric site of the first enzyme, inhibiting the pathway when the product is abundant.