Biology 1: Energy, Enzymes, and Metabolism

Flashcards covering the principles of biological energy transformations, thermodynamics, enzyme kinetics, regulation, and an introduction to glucose metabolism based on Lecture 10.

Energy

The capacity to do work, or the capacity to change.

Potential Energy

Stored energy, existing as chemical bonds, concentration gradients, or charge imbalances.

Kinetic Energy

The energy of movement.

First Law of Thermodynamics

The law stating that the total amount of energy before a transformation equals the total amount after; energy is neither created nor lost.

Second Law of Thermodynamics

The law stating that although total energy remains constant, the amount of usable energy (free energy) decreases and unusable energy (entropy) increases after any transformation.

Entropy ($S$)

A measure of disorder in a system; it tends to increase during energy transformations.

Enthalpy ($H$)

The total energy of a system, defined by the formula $H = G + TS$.

Free Energy ($G$)

The usable energy in a system available to perform work.

Change in Free Energy ($\Delta G$)

The difference between the free energy of the products and the free energy of the reactants: $\Delta G = G_{products} - G_{reactants}$.

Exergonic Reaction

A reaction where $\Delta G < 0$ and free energy is released.

Endergonic Reaction

A reaction where $\Delta G > 0$ and an input of free energy is required.

Metabolism

The sum total of all chemical reactions occurring within a biological system.

Anabolic Reactions

Metabolic reactions where complex molecules are synthesized from simple molecules; they are endergonic ($\Delta G > 0$) and store energy in chemical bonds.

Catabolic Reactions

Metabolic reactions where complex molecules are broken down into simpler ones; they are exergonic ($\Delta G < 0$) and release energy.

Adenosine Triphosphate (ATP)

A molecule consisting of adenine, ribose, and three phosphate groups that captures and transfers free energy.

ATP Hydrolysis

The exergonic reaction where ATP reacts with water to form ADP and inorganic phosphate ($P_i$), releasing approximately $30\,kJ\,mol^{-1}$ ($7.3\,kcal\,mol^{-1}$) of energy.

Coupling Reactions

The process of pairing an exergonic reaction (like ATP hydrolysis) with an endergonic reaction to make the overall $\Delta G$ negative and allow the reaction to proceed.

Activation Energy ($E_a$)

The initial energy input required to start a chemical reaction; it determines the rate of the reaction.

Enzyme

A biological catalyst (usually a protein) that speeds up chemical reactions by lowering the activation energy ($E_a$) without changing the reaction equilibrium ($\Delta G$).

Active Site

The specific region on an enzyme where substrates bind and the reaction is catalyzed.

Coenzymes

Non-protein, carbon-containing molecules required for the function of some enzymes.

Competitive Inhibitor

A subtsance that binds to the active site of an enzyme, competing directly with the substrate.

Noncompetitive Inhibitor

A substance that binds to an enzyme at a site other than the active site, changing the enzyme's shape so that the active site no longer functions.

Allosteric Regulation

A change in enzyme shape caused by the noncompetitive binding of an inhibitor or activator, which alters the affinity of the active site for the substrate.

Feedback Inhibition

A mechanism where the end-product of a metabolic pathway allosterically inhibits the enzyme of the commitment step to shut down its own production.

Redox Reaction

A chemical reaction involving the transfer of electrons from one substance (oxidation) to another (reduction).

Oxidation

The loss of one or more electrons by an atom, ion, or molecule.

Reduction

The gain of one or more electrons by an atom, ion, or molecule.

Reducing Agent

The reactant that becomes oxidized by donating electrons (the electron donor).

Oxidizing Agent

The reactant that becomes reduced by accepting electrons (the electron acceptor).

Electronegativity

The attractive force that an atomic nucleus exerts on shared electrons in a covalent bond.

NAD (Nicotinamide adenine dinucleotide)

An electron carrier coenzyme that exists in an oxidized form ($NAD^+$) and a reduced form ($NADH$).

Glycolysis

A metabolic pathway that breaks down glucose into pyruvate, occurring in the cytoplasm of both prokaryotes and eukaryotes.

Fermentation

A catabolic pathway that occurs in the absence of oxygen ($O_2$) to produce lactate or alcohol from pyruvate.