Bioenergetics, Metabolism, and Enzyme Regulation

Vocabulary review covering cellular respiration, glycolysis stoichiometry, thermodynamics in biology, and enzyme regulation mechanisms.

Second Law of Thermodynamics (in Living Organisms)

The thermodynamic principle whereby an organism can decrease its own internal entropy during growth because it produces a greater increase in entropy in its surrounding environment.

First Law of Thermodynamics (in Living Organisms)

The law of energy conservation which dictates that an organism cannot create energy and must ultimately obtain all of the necessary energy for life from its environment.

Competitive Inhibition

A form of enzyme inhibition where an inhibitor competes directly with the substrate for the active site, which can be overcome by increasing substrate concentration.

Allosteric Inhibition

Enzyme regulation in which an inhibitor binds to a regulatory site away from the active site, altering the enzyme's three-dimensional shape and preventing substrate binding.

Phosphofructokinase (PFK)

A key glycolytic enzyme catalyzing an early energy-investment step that undergoes allosteric inhibition when ATP binds away from the active site.

Protein Kinases and Protein Phosphatases

Enzymes that act as molecular switches for protein activity by attaching (kinases) or removing (phosphatases) phosphate groups, altering a target protein's charge to induce a conformational change.

Phosphorylated Molecule

A molecule that has received a phosphate group, gaining increased chemical potential energy that primes it to perform cellular work.

Chemical Equilibrium

A dynamic state of a chemical reaction where forward and reverse reaction rates are equal, resulting in a system that can perform no work.

ATP (Adenosine Triphosphate)

A central metabolic molecule that drives cellular processes by energetically coupling exergonic and endergonic reactions.

Exergonic Metabolic Process

A spontaneous, energy-releasing pathway—such as $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O}$—that can occur without a net influx of energy from another reaction.

Cellular Respiration

A catabolic, exergonic metabolic pathway in which organic molecules are broken down with a negative change in free energy ($\text{delta}G < 0$).

High-Energy Foods (Carbohydrates and Fats)

Nutrient molecules rich in chemical energy because they contain abundant electrons associated with hydrogen atoms.

Aerobic Electron Flow Sequence

The downhill energy path traveled by electrons during aerobic cellular respiration: $\text{food} \rightarrow \text{NADH} \rightarrow \text{electron transport chain} \rightarrow \text{oxygen}$.

Reduced Electron Carrier Pathways

The metabolic stages of cellular respiration that generate reduced coenzymes (NADH and $\text{FADH}_2$), consisting of glycolysis, pyruvate oxidation, and the citric acid cycle.

Glycolysis Stoichiometry (ATP Yield)

The ATP balance during the oxidation of one mole of glucose to pyruvate, where $2\,\text{moles}$ of ATP are used (energy-investment) and $4\,\text{moles}$ of ATP are produced (energy-payoff).

Inner Mitochondrial Membrane Pores

Disruptive openings that immediately halt mitochondrial ATP synthesis by allowing the leakage of hydrogen ions ($\text{H}^+$) and destroying the electrochemical gradient.

Proton Gradient

An electrochemical concentration gradient across a membrane that directly supplies the potential energy driving the majority of ATP synthesis during cellular respiration.

Chemiosmotic Synthesis of ATP

The ATP production mechanism that requires electron transport along the inner mitochondrial membrane to be coupled directly to proton transport across that same membrane.

Distant Amino Acid Mutation (Enzyme Specificity)

A mutation located away from the active site that modifies an enzyme's substrate specificity by altering the overall shape and folding of the protein.