Campbell Biology Chapter 8: Energy and Metabolism

Vocabulary practice flashcards covering thermodynamics, free energy, metabolic pathways, ATP energetics, redox reactions, and enzyme regulation based on Campbell Biology Chapter 8.

Metabolism

The totality of an organism's chemical reactions, functioning as an emergent property of life that arises from orderly molecular interactions within the cell.

Metabolic Pathway

A series of defined chemical steps starting with a specific molecule and ending with a product, where each step is catalyzed by a specific enzyme.

Catabolism (Catabolic Pathways)

Metabolic pathways that release energy by breaking down complex molecules into simpler compounds, such as the breakdown of glucose during cellular respiration.

Anabolism (Anabolic Pathways)

Metabolic pathways that consume energy to synthesize complex molecules from simpler ones, such as building proteins from amino acids.

Bioenergetics

The study of how energy flows through living organisms and how organisms manage their energy resources.

Kinetic Energy

Energy associated with the relative motion of objects that is actively performing work.

Potential Energy

Energy that matter possesses because of its location or spatial arrangement, including the capacity to do work stored in chemical bonds.

Thermodynamics

The study of the energy transformations that occur in a collection of matter.

Isolated System

A system that is physically separated from its surroundings and unable to exchange either energy or matter with them, approximated by liquid in a thermos.

Open System

A system in which energy and matter can be continuously transferred between the system and its surroundings; all living organisms are open systems.

First Law of Thermodynamics

The principle of conservation of energy stating that the total energy in a closed system remains constant; energy can be transferred and transformed, but cannot be created or destroyed.

Second Law of Thermodynamics

The principle stating that every energy transfer or transformation increases the entropy of the universe because no energy conversion is $100\%$ efficient, with some energy lost as heat.

Entropy

A quantitative measure of disorder or randomness, representing the spreading of energy throughout the universe.

Free Energy ($G$)

The portion of a biological system's energy that is available to perform work when temperature and pressure are uniform throughout the system.

Dynamic Equilibrium

A state in which forward and reverse reaction rates are equal, resulting in constant relative concentrations of reactants and products and a minimum free energy ($G$), preventing work from being done.

Exergonic Reaction

A spontaneous chemical reaction accompanied by the net release of free energy, in which the free energy of the products is lower than that of the reactants ($\Delta G < 0$).

Endergonic Reaction

A non-spontaneous chemical reaction that absorbs free energy from its surroundings, yielding products with higher free energy than the reactants ($\Delta G > 0$).

Energy Coupling

In cellular metabolism, the use of energy released from an exergonic process to drive an endergonic, energy-consuming process, primarily mediated by ATP.

ATP (Adenosine Triphosphate)

A nucleotide functioning as the primary energy currency of cells, composed of the nitrogenous base adenine, the sugar ribose, and a chain of three phosphate groups.

ATP Cycle

The continuous cyclical shuttling of inorganic phosphate and energy whereby ATP is hydrolyzed into ADP and $P_i$ to release energy for cellular work, and regenerated by phosphorylating ADP using catabolic energy.

Redox Reactions

Paired chemical reactions involving the complete or partial transfer of electrons between substances, wherein oxidation and reduction occur simultaneously for cellular energy harvesting.

Oxidation

The complete or partial loss of electrons from a substance in a redox reaction, which generally releases energy.

Reduction

The complete or partial gain of electrons by a substance in a redox reaction, which generally increases the substance's chemical energy.

Enzyme

A macromolecular catalyst (typically a protein, or an RNA molecule known as a ribozyme) that accelerates the rate of a chemical reaction without being consumed by the process.

Catalyst

A chemical agent that speeds up the rate of a chemical reaction by lowering its activation energy barrier without participating as a consumed reactant.

Activation Energy ($E_A$)

The initial investment of energy required to contort reactant molecules into an unstable transition state so that chemical bonds can break and reform.

Active Site

The specific region of an enzyme molecule, usually a pocket or groove, where the substrate binds and catalysis takes place.

Induced Fit

The slight conformational change in the shape of an enzyme's active site and substrate that occurs upon binding, ensuring a tighter embrace and positioning chemical groups for catalysis.

Enzyme-Substrate Complex

A short-lived, unstable intermediate formed when an enzyme binds non-covalently to its specific reactant molecule(s).

Cofactor

Any nonprotein molecule or ion that is required for the proper functioning of an enzyme; can be inorganic, such as metal ions ($\text{Ca}^{2+}$, $\text{Mg}^{2+}$, $\text{Fe}^{3+}$), or organic.

Coenzyme

An organic cofactor that assists enzyme activity, often derived from or consisting of vitamins, such as $\text{NAD}^+$, $\text{NADP}^+$, and $\text{FAD}$.

Apoenzyme

The inactive protein component of an enzyme that requires the binding of a specific cofactor or coenzyme to become catalytically active.

Optimal Temperature

The specific temperature at which an enzyme's catalytic rate is fastest; for typical human enzymes this is approximately $37\,^{\circ}\text{C}$, while thermophilic bacterial enzymes operate optimally near $77\,^{\circ}\text{C}$.

Optimal pH

The specific pH level at which an enzyme maintains its optimal three-dimensional conformation and highest reaction rate, such as $\text{pH } 2$ for pepsin and $\text{pH } 8$ for trypsin.

Competitive Inhibitor

A regulatory substance that reduces the activity of an enzyme by mimicking the structure of the substrate and directly competing for entry into the active site.

Noncompetitive Inhibitor

A regulatory molecule that impedes enzymatic reactions by binding to an allosteric site away from the active site, altering the enzyme's conformation so the active site becomes ineffective.

Allosteric Site

A specific receptor site on an enzyme distinct from the catalytic active site, where regulatory molecules bind to stabilize either the active or inactive form of the enzyme.

Feedback Inhibition

A metabolic control mechanism in which the final end product of a multi-step pathway allosterically binds to and inhibits an early enzyme (such as isoleucine inhibiting threonine deaminase), shutting down the pathway to prevent resource waste.