AP Bio Unit 3 Quiz

Metabolism

The totality of an organism's chemical reactions, consisting of catabolic and anabolic pathways that manage material and energy resources.

Metabolic pathway

A linked sequence of biochemical reactions catalyzed by specific enzymes, transforming a starting precursor molecule into a final product.

Catabolic pathway

A metabolic pathway that releases free energy by breaking down complex molecules into simpler compounds (e.g., cellular respiration).

Anabolic pathway

A metabolic pathway that consumes energy to build complicated molecules from simpler building blocks (e.g., protein synthesis from amino acids).

Bioenergetics

The quantitative study of energy flow, transfer, and transformation through living biological systems.

Kinetic energy vs. Potential energy

Energy associated with relative motion of matter versus stored energy possessed by matter due to its location, spatial arrangement, or structure.

Thermal energy

A form of kinetic energy associated with the random movement of atoms or molecules, transferred between bodies of matter as heat.

Chemical energy

A form of potential energy available for release during a chemical reaction, stored within molecular bonds.

First law of thermodynamics

The principle of conservation of energy stating that energy can be transferred and transformed, but cannot be created or destroyed.

Second law of thermodynamics

The physical principle stating that every spontaneous energy transfer or transformation increases the total entropy of the universe.

Entropy

A quantitative thermodynamic measure of randomness, molecular disorder, or dispersed unusable thermal energy in a system.

Adenosine triphosphate ($ATP$)

The primary energy-transfer molecule of cells, composed of ribose, adenine, and three phosphate groups, driving work via high-energy bond hydrolysis.

Energy coupling

The cellular strategy of using an exergonic reaction (such as $ATP$ hydrolysis) to power an energetically unfavorable endergonic reaction.

Activation energy ($E_a$)

The initial investment of energy required to contort reactant bonds into an unstable transition state so a reaction can proceed.

Enzyme

A macromolecular biological catalyst (typically a protein) that accelerates reaction rates by lowering activation energy without being altered or consumed.

Active site

The specific pocket or groove on a catalytic protein where substrate molecules bind and undergo chemical reaction.

Substrate

The specific reactant molecule upon which an enzyme binds and acts.

Induced fit

The subtle conformational change of an enzyme's active site around a substrate to optimize catalytic interaction.

Competitive inhibitor

A regulatory molecule that reduces enzyme activity by binding directly to the active site, physically mimicking and blocking the normal substrate.

Noncompetitive inhibitor

A regulatory molecule that reduces enzyme efficacy by binding to an allosteric site away from the active site, inducing a conformational change.

Allosteric regulation

The control of enzyme activity occurring when a regulatory molecule binds to a site other than the catalytic center, stabilizing either active or inactive forms.

Environmental factors affecting enzyme activity

Temperature, pH, and concentration of both catalyst and substrate, which influence molecular collisions, chemical bonding, and tertiary structure.

Enzyme denaturation

The disruption of an enzyme's native secondary and tertiary protein structure caused by extreme temperature or pH shifts, destroying active site function.

Phosphorylation

The covalent addition of an inorganic phosphate group to a molecule, often altering protein conformation, activity, or chemical reactivity.

Cellular respiration

A catabolic pathway in which fuel molecules (such as glucose) are systematically oxidized to extract energy and synthesize $ATP$, releasing $CO_2$ and $H_2O$.

Aerobic respiration vs. Fermentation

Complete catabolism requiring molecular oxygen as the final electron acceptor versus an anaerobic catabolic pathway producing $ATP$ solely via substrate-level phosphorylation without an electron transport chain.

Oxidation vs. Reduction

The loss of electrons and associated hydrogen atoms from a substance versus the gain of electrons and associated hydrogen atoms by a substance.

$NAD^+$ / $NADH$

A coenzyme and central mobile electron carrier that accepts two electrons and one proton during catabolic redox reactions to store reducing power.

Glycolysis

A ten-step cytoplasmic pathway that splits one glucose ($C_6H_{12}O_6$) into two pyruvate molecules, producing a net of $2\,ATP$ and $2\,NADH$.

Pyruvate oxidation

The mitochondrial transition reaction converting pyruvate to acetyl $CoA$, releasing one $CO_2$ and generating one $NADH$ per pyruvate.

Citric acid cycle (Krebs cycle)

An eight-step cyclical pathway in the mitochondrial matrix that oxidizes acetyl groups to $CO_2$, yielding $NADH$, $FADH_2$, and $ATP$/$GTP$.

Electron transport chain ($ETC$)

A collection of protein complexes embedded in the inner mitochondrial cristae that shuttle electrons down an exergonic path to pump protons ($H^+$).

Oxygen's primary role in cellular respiration

Acting as the terminal electron acceptor at the conclusion of the electron transport chain, pulling electrons and combining with protons ($H^+$) to yield $H_2O$.

Proton-motive force

The electrochemical gradient generated by pumping hydrogen ions ($H^+$) from the mitochondrial matrix into the intermembrane space.

Chemiosmosis

The movement of ions across a semipermeable membrane down their electrochemical gradient to power biochemical work such as $ATP$ generation.

$ATP$ synthase

A membrane-bound protein complex that harnesses the proton-motive force to catalyze the addition of inorganic phosphate to $ADP$.

Oxidative phosphorylation

The metabolic stage combining electron transfer along an electron transport chain with chemiosmotic synthesis to generate the majority of cellular $ATP$.

Mitochondrial structure suited for respiration

Folded inner cristae provide extensive surface area for electron transport chains, while the compartmentalized intermembrane space and matrix maintain steep proton gradients.

Alcohol fermentation

An anaerobic catabolic pathway converting pyruvate to ethanol and $CO_2$, regenerating $NAD^+$ to maintain continuous glycolysis.

Lactic acid fermentation

An anaerobic catabolic pathway where pyruvate is reduced directly by $NADH$ to form lactate, regenerating $NAD^+$ without producing $CO_2$.