(Lecture 4) Metabolism and Cellular Respiration

Vocabulary practice flashcards covering basic thermodynamics, enzymatic activity and regulation, stages of cellular respiration, and anaerobic fermentation processes based on the lecture.

Metabolism

The study of chemical reactions in a cell or organism, examining how reagents produce products, transfer energy, and convert food into energy to sustain life.

Catabolic Pathways (Catabolism)

Metabolic pathways that release energy by breaking down complex molecules into simpler compounds, such as degrading complex sugars into smaller sugars.

Anabolic Pathways (Anabolism)

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

Kinetic Energy

The form of energy associated with the motion of an object or molecule.

Potential Energy

Energy that matter possesses due to its spatial location or its structure.

Thermal Energy (Heat)

A form of kinetic energy associated with how fast atoms and molecules move or vibrate inside a solid or liquid.

Chemical Energy

A form of potential energy stored in molecules based on the proximity and bonds between their atoms, such as the energy held in the phosphate groups of $ATP$.

First Law of Thermodynamics

The principle stating that the energy of the universe is constant; energy cannot be created or destroyed, but can only be transferred and transformed.

Second Law of Thermodynamics

The principle stating that every energy transfer increases the entropy or disorganization of the universe, resulting in some energy being lost as heat.

Exergonic Reaction

A spontaneous chemical reaction that naturally releases free energy and moves the participating molecules toward equilibrium.

Endergonic Reaction

A nonspontaneous chemical reaction that absorbs free energy from its surroundings, moving away from equilibrium and producing products with higher energy than the reactants.

ATP (Adenosine Triphosphate)

The primary energy-transporting molecule that powers cellular work, composed of adenine, ribose, and three negatively charged phosphate groups that repel each other.

Hydrolysis of ATP

A reaction requiring water that breaks the terminal phosphate bond of $ATP$, releasing a phosphate group, forming $ADP$, and releasing stored energy.

Phosphorylated Intermediate

The recipient molecule that receives a released phosphate group from $ATP$, thereby gaining energy to perform cellular work.

Enzymes

Catalytic proteins that accelerate and facilitate specific chemical reactions in living cells without being consumed by the reaction.

Activation Energy ($E_a$)

The initial investment of free energy—often supplied as thermal energy from the surrounding environment—required to initiate a chemical reaction.

Substrate

The specific reactant molecule upon which an enzyme acts.

Active Site

The specialized catalytic region on an enzyme's three-dimensional protein structure where the substrate binds to undergo a chemical reaction.

Competitive Inhibitor

A regulatory or toxic molecule that mimics the substrate and binds directly to the active site of an enzyme, physically preventing the substrate from attaching.

Noncompetitive Inhibitor

A molecule that binds to a region of the enzyme other than the active site, inducing a conformational shape change that prevents the substrate from binding.

Sarin Gas

A nerve weapon that binds to the enzyme acetylcholinesterase, blocking the degradation of acetylcholine and leading to lethal hyperactivation of the nervous system.

Allosteric Regulation

A regulatory mechanism where a molecule binds to an enzyme at a specific regulatory site, stabilizing either its active form to stimulate reaction or its inactive form to inhibit it.

Cooperativity

A form of allosteric regulation where the binding of one substrate molecule to an active site alters the shape of the enzyme, increasing the activity of other active sites.

Feedback Inhibition

A metabolic control mechanism where the end product of a synthetic pathway binds to an enzyme operating early in that pathway to stop its own overproduction.

Redox Reactions

Oxidation-reduction chemical reactions involving the transfer of electrons between reactants, transferring stored chemical energy.

Oxidation

The loss of negatively charged electrons from a chemical substance, making that substance more positively charged.

Reduction

The gain of negatively charged electrons by a chemical substance, making that substance more negatively charged.

NAD+ (Nicotinamide Adenine Dinucleotide)

A coenzyme electron shuttle that acts as an oxidizing agent by accepting two electrons and a proton to become reduced to $NADH$.

Glycolysis

An anaerobic process occurring in the cytoplasm that splits one molecule of glucose into two molecules of pyruvate, generating a net of $2\text{ ATP}$, $2\text{ NADH}$, and $2\text{ }H_2O$.

Energy Investment Phase

The initial stage of glycolysis in which the cell expends $2\text{ ATP}$ molecules to initiate the breakdown of glucose.

Energy Payoff Phase

The second stage of glycolysis in which the cell forms $4\text{ ATP}$, $2\text{ NADH}$, and $2\text{ pyruvate}$ molecules.

Pyruvate Oxidation

The aerobic mitochondrial process that converts pyruvate into acetyl CoA, releasing $CO_2$ and transferring electrons to reduce $NAD^+$ to $NADH$.

Citric Acid Cycle (Krebs Cycle)

A cyclic series of reactions in the mitochondria that oxidizes acetyl CoA derivatives, producing $3\text{ }CO_2$, $1\text{ ATP}$, $3\text{ NADH}$, and $1\text{ }FADH_2$ per turn.

Oxidative Phosphorylation

The stage of cellular respiration consisting of the electron transport chain and chemiosmosis that synthesizes up to $34\text{ ATP}$ using high-energy electrons transported by $NADH$ and $FADH_2$.

Electron Transport Chain

A collection of iron- and sulfur-containing protein complexes located in the inner mitochondrial membrane that use electrons from $NADH$ and $FADH_2$ to pump $H^+$ protons into the intermembrane space.

ATP Synthase

A rotary membrane enzyme complex powered by the flow of $H^+$ protons across the inner mitochondrial membrane to catalyze the synthesis of $ATP$ from $ADP$ and inorganic phosphate.

Chemiosmosis

An energy-coupling mechanism that uses energy stored in a proton gradient (proton-motive force) across the mitochondrial membrane to drive cellular work, specifically $ATP$ synthesis.

Fermentation

An anaerobic process that couples glycolysis with pathways to regenerate $NAD^+$ from $NADH$, allowing the continuous generation of $ATP$ when oxygen is absent.

Alcohol Fermentation

A pathway in which pyruvate is converted to acetaldehyde and then to ethanol, producing carbon dioxide and regenerating $NAD^+$ without requiring oxygen.

Lactic Acid Fermentation

A metabolic pathway in which pyruvate is directly reduced to lactate to generate $ATP$ and regenerate $NAD^+$ in the absence of oxygen, used by human muscle cells and certain bacteria.

Saccharomyces cerevisiae

The species of single-celled, egg-shaped microscopic yeast used in baking and brewing that ferments sugars into carbon dioxide and ethanol.