MCAT key terms

A rapid, self-propagating change in a neuron's membrane voltage triggered when depolarization reaches threshold, driven by voltage-gated sodium influx followed by potassium efflux and refractory recovery.

The steady negative voltage across a neuron's membrane at rest, maintained mainly by potassium leak channels and the sodium-potassium pump establishing ion concentration gradients.

The membrane voltage a neuron must reach to open enough voltage-gated sodium channels for an action potential to fire; signals below it decay without propagating.

The integration of excitatory and inhibitory postsynaptic potentials over space and time at a neuron's trigger zone, determining whether threshold is reached.

An ATP-driven membrane protein that exports three sodium ions and imports two potassium ions per cycle, sustaining the gradients that underlie resting potential and secondary active transport.

The quantitative study of reaction rates catalyzed by enzymes, described by parameters such as maximum velocity and the substrate concentration giving half-maximal rate.

The substrate concentration at which an enzyme works at half its maximum velocity; a low value indicates high substrate affinity under standard assumptions.

A reversible inhibitor that binds the enzyme's active site, raising the substrate concentration needed for half-maximal rate while leaving maximum velocity unchanged.

Control of enzyme or protein activity by a molecule binding a site other than the active site, shifting the protein between active and inactive conformations.

Binding of one ligand changing a protein's affinity for subsequent ligands, producing a sigmoidal saturation curve and sharpening the response to small concentration changes.

The cytosolic pathway that splits one glucose into two pyruvate molecules, yielding net ATP and NADH without requiring oxygen.

ATP production driven by the proton gradient built by the electron transport chain, with oxygen as the terminal electron acceptor in aerobic respiration.

ATP synthesis powered by protons flowing down their electrochemical gradient through a membrane enzyme complex, coupling electron transport to phosphorylation.

Anaerobic regeneration of NAD+ from NADH by transferring electrons to pyruvate or its derivatives, allowing glycolysis to continue without an electron transport chain.

Patterns of trait transmission explained by segregation of allele pairs and independent assortment of genes on different chromosomes during gamete formation.

The allele and genotype frequencies expected in an idealized population with no selection, mutation, migration, drift, or nonrandom mating; deviations suggest evolution is occurring.

Random fluctuation of allele frequencies between generations, strongest in small populations, which can fix or eliminate alleles independent of fitness.

Movement of alleles between populations through migration and interbreeding, tending to reduce genetic differences among groups.

Genes close together on the same chromosome that tend to be inherited together, with recombination frequency reflecting their physical separation.

Differential survival and reproduction of individuals whose heritable traits better fit the environment, changing allele frequencies across generations.

A system at equilibrium shifts to partially offset a change in concentration, pressure, or temperature, restoring a new equilibrium position.

The ratio of product to reactant activities at equilibrium for a given reaction; its magnitude indicates whether products or reactants are favored.

A thermodynamic quantity whose sign predicts reaction spontaneity at constant temperature and pressure; negative values indicate favorable, spontaneous processes.

The equilibrium constant for loss of a proton from an acid; a smaller value means a weaker acid, and its negative logarithm gives the pKa.

A solution of a weak acid and its conjugate base that resists pH change when small amounts of strong acid or base are added, working best near its pKa.

A relationship linking solution pH to the pKa of a buffer and the ratio of conjugate base to weak acid concentrations.

The three-dimensional arrangement of atoms in a molecule, including chirality and geometric isomerism, which can alter biological activity and reaction outcomes.

A property of molecules that are non-superimposable on their mirror images, usually due to a carbon bearing four different substituents; enantiomers differ in handedness.

An electron-rich species that donates an electron pair to an electron-poor center, driving substitution and addition reactions in organic chemistry.

The study of how liquids and gases flow, including relationships among pressure, velocity, and cross-sectional area in moving fluids.

For steady, nonviscous flow along a streamline, faster-moving fluid has lower pressure, explaining lift and flow through narrowed regions.

A relationship stating that flow through a tube rises with the fourth power of radius and the pressure difference, and falls with viscosity and length.

Learning in which the frequency of a behavior changes because of consequences such as reinforcement or punishment.

Learning in which a neutral stimulus paired repeatedly with an unconditioned stimulus comes to elicit a conditioned response on its own.

Weakening and eventual disappearance of a learned response when the conditioned or reinforcing stimulus is no longer presented.

The rule determining how often and when a consequence follows a behavior, strongly affecting how quickly a response is learned and how resistant it is to extinction.

The tendency to seek, interpret, and remember information that supports existing beliefs while discounting contrary evidence.

Judging the likelihood of an event by how easily examples come to mind, which can overweight vivid or recent occurrences.

The underlying prevalence of a condition in a population, which should be combined with test evidence when estimating the probability of a diagnosis.

The property of a hypothesis being testable through observations that could show it false, a core criterion distinguishing scientific claims from unfalsifiable ones.

A comparison group that does not receive the treatment under study, used to isolate the effect of the independent variable from other influences.

Placing participants into experimental conditions by chance so groups are similar on average, supporting causal inference by limiting confounding.

An unmeasured factor associated with both the presumed cause and the outcome, which can create a spurious association if not controlled.

A result unlikely to occur by chance alone under a specified null hypothesis, conventionally judged against a preselected probability threshold.

A standardized measure of the magnitude of a difference or association, complementing significance testing by showing practical importance.

A range of plausible values for a population parameter, constructed so that a stated proportion of such intervals would contain the true value across repeated samples.