MCAT Comprehensive Vocabulary Flashcards

Key vocabulary terms and concise definitions spanning chemistry, biochemistry, biology, physics, and research methods for comprehensive MCAT review.

Atomic Number (Z)

Number of protons in an atom; identifies the element.

Mass Number (A)

Total number of protons and neutrons in an atom’s nucleus.

Pauli Exclusion Principle

No two electrons in an atom can have the same set of four quantum numbers.

Hund’s Rule

Electrons fill degenerate orbitals singly before pairing to maximize total spin.

Diamagnetic

All electrons are paired; substance is repelled by a magnetic field.

Paramagnetic

Contains one or more unpaired electrons; attracted into a magnetic field.

Effective Nuclear Charge (Zeff)

Net positive charge experienced by valence electrons; increases left→right across a period.

Electronegativity (EN)

Atom’s ability to attract electrons in a chemical bond; measured by Pauling scale.

Ionization Energy

Energy required to remove the most loosely bound electron from a gaseous atom.

Electron Affinity

Energy released when an atom gains an electron to form an anion.

Lewis Acid

Electron-pair acceptor in a chemical reaction.

Lewis Base

Electron-pair donor in a chemical reaction.

Covalent Bond

Chemical bond formed by the sharing of valence electrons between atoms.

Ionic Bond

Electrostatic attraction between oppositely charged ions after electron transfer.

Sigma (σ) Bond

Single covalent bond formed by head-to-head orbital overlap.

Pi (π) Bond

Bond formed by sideways overlap of p-orbitals; present in double/triple bonds.

Hybridization

Mixing of atomic orbitals to form equivalent hybrid orbitals (sp, sp2, sp3 etc.).

Formal Charge

Valence electrons − (dots + sticks); estimates charge on an atom in a molecule.

Arrhenius Equation

k = A·e^(−Ea/RT); relates rate constant to temperature and activation energy.

Rate-Determining Step

Slowest elementary step in a reaction mechanism; controls overall rate.

Le Châtelier’s Principle

A system at equilibrium responds to stress by shifting to relieve the stress.

Standard Conditions

298 K, 1 atm, 1 M concentrations; used for thermodynamics and electrochemistry.

Hess’s Law

Total enthalpy change equals sum of enthalpy changes for individual steps.

Raoult’s Law

Vapor-pressure of solution equals mole fraction of solvent times vapor-pressure of pure solvent (P = X·P°).

Boiling-Point Elevation

ΔTb = i·Kb·m; solute raises boiling point proportional to molality and van’t Hoff factor.

Buffer

Solution of weak acid/base and its conjugate that resists pH changes.

Henderson–Hasselbalch Equation

pH = pKa + log([A⁻]/[HA]); relates pH to buffer ratio.

Oxidizing Agent

Species that gains electrons and gets reduced in a redox reaction.

Reducing Agent

Species that loses electrons and gets oxidized in a redox reaction.

Galvanic Cell

Electrochemical cell with spontaneous redox reaction (ΔG

Electrolytic Cell

Cell where non-spontaneous redox reaction is driven by external voltage (ΔG>0).

Nernst Equation

E = E° − (0.0592/n)·log Q; calculates cell potential under non-standard conditions.

pI (Isoelectric Point)

pH at which a molecule carries no net electrical charge.

Competitive Inhibitor

Binds active site; increases Km, no change in Vmax.

Noncompetitive Inhibitor

Binds allosteric site; decreases Vmax, Km unchanged.

Michaelis Constant (Km)

Substrate concentration at which reaction rate is half of Vmax; measures affinity.

Cooperative Binding

Substrate binding increases affinity at other active sites; produces sigmoidal kinetics.

Glycolysis

Anaerobic pathway converting glucose to pyruvate, producing 2 ATP and 2 NADH.

Pyruvate Dehydrogenase Complex

Converts pyruvate to acetyl-CoA, producing NADH and CO₂.

Citric Acid Cycle

Mitochondrial cycle oxidizing acetyl-CoA to CO₂, generating NADH, FADH₂, and GTP.

Electron Transport Chain

Series of complexes that transfer electrons to oxygen and pump protons to create proton-motive force.

Oxidative Phosphorylation

ATP synthesis via ATP synthase powered by proton gradient across inner mitochondrial membrane.

Beta-Oxidation

Mitochondrial breakdown of fatty acids into acetyl-CoA units with FADH₂ & NADH production.

Gluconeogenesis

Hepatic synthesis of glucose from non-carbohydrate precursors during fasting.

Pentose Phosphate Pathway

Cytosolic pathway generating NADPH and ribose-5-phosphate for nucleotide synthesis.

Insulin

Pancreatic β-cell peptide hormone that lowers blood glucose and promotes anabolic processes.

Glucagon

Pancreatic α-cell peptide hormone that raises blood glucose via glycogenolysis and gluconeogenesis.

Cortisol

Adrenal corticosteroid stress hormone that increases gluconeogenesis and protein catabolism.

Gene

Sequence of DNA that codes for a functional product (RNA or protein).

Transcription

Synthesis of RNA from a DNA template by RNA polymerase.

mRNA

Messenger RNA; carries genetic information from nucleus to ribosome.

tRNA

Transfer RNA; delivers specific amino acids to ribosome during translation.

Codon

Three-nucleotide mRNA sequence that specifies an amino acid.

Promoter

DNA region where RNA polymerase binds to initiate transcription.

Operon

Cluster of genes under control of a single promoter in prokaryotes.

PCR (Polymerase Chain Reaction)

In vitro technique to amplify specific DNA sequences via thermal cycling and Taq polymerase.

Southern Blot

Lab method to detect specific DNA sequences after electrophoresis.

Western Blot

Technique to identify specific proteins using antibodies after SDS-PAGE.

Osmotic Pressure (π)

π = iMRT; pressure required to stop osmosis, proportional to solute concentration.

Laminar Flow

Smooth orderly fluid motion characterized by parallel layers and low Reynolds number.

Poiseuille’s Law

Q = (πr⁴ΔP)/(8ηL); flow rate of viscous fluid through a cylindrical pipe.

Bernoulli’s Equation

P + ½ρv² + ρgh = constant; describes conservation of energy in fluid flow.

Snell’s Law

n₁ sinθ₁ = n₂ sinθ₂; governs refraction of light between media.

Total Internal Reflection

Complete reflection of light inside a medium when incidence angle exceeds critical angle.

Diffraction

Bending/spreading of waves when they encounter an obstacle or slit comparable in size to wavelength.

Photoelectric Effect

Ejection of electrons when light of sufficient frequency strikes a metal; evidence for particle nature of light.

Half-Life (t½)

Time required for half of a radioactive sample to decay.

Coulomb’s Law

Electrostatic force F = k·|q₁q₂|/r² between two point charges.

Electric Field (E)

Force per unit charge created by a source charge; E = kQ/r².

Capacitance (C)

Ability to store charge per unit voltage; C = Q/ΔV.

Faraday’s Constant

F = 96,485 C mol⁻¹; charge of one mole of electrons.

Elastic Potential Energy

Stored energy in a stretched/compressed spring; U = ½kx².

Work-Energy Theorem

Net work on an object equals its change in kinetic energy (W = ΔK).

Impulse

Change in momentum; J = F·Δt = Δp.

Entropy (S)

Measure of energy dispersal; for reversible processes, ΔS = Qrev/T.

Zwitterion

Molecule with equal positive and negative charges but overall neutral, common for amino acids at pI.

Antibody (Immunoglobulin)

Y-shaped glycoprotein that binds specific antigens to aid immune response.

Ligand-Gated Channel

Membrane protein that opens/closes in response to binding of a chemical messenger.

Signal Peptide

Short N-terminal sequence that directs a nascent protein to the endoplasmic reticulum.

Allosteric Regulation

Modulation of enzyme activity via binding at a site other than the active site, causing conformational change.

Michaelis-Menten Equation

v = (Vmax·[S])/(Km + [S]); describes rate of enzyme-catalyzed reactions.

Kcat (Turnover Number)

Number of substrate molecules converted to product per enzyme per second under saturating substrate.

Lineweaver–Burk Plot

Double-reciprocal graph of 1/v vs 1/[S] used to determine Km and Vmax.

Second Messenger

Intracellular molecule (e.g., cAMP, IP₃) that transmits signals from receptors to target molecules.

Epigenetics

Heritable changes in gene expression not involving alterations in DNA sequence (e.g., methylation, histone acetylation).

Aneuploidy

Abnormal number of chromosomes due to nondisjunction during meiosis or mitosis.

Hardy–Weinberg Equilibrium

Allele and genotype frequencies remain constant in an ideal population (p² + 2pq + q² =1).

Hill Coefficient

Parameter indicating degree of cooperative binding in an enzyme or receptor; >1 positive cooperativity.

Bohr Effect

Decrease in hemoglobin’s oxygen affinity at low pH/high CO₂, facilitating oxygen release in tissues.

Tidal Volume (TV)

Volume of air inhaled or exhaled in a normal breath.

Systolic Pressure

Maximum arterial pressure during ventricular contraction.

Hormone

Signaling molecule secreted into bloodstream that regulates physiology and behavior.

Second Law of Thermodynamics

Entropy of an isolated system never decreases; processes proceed toward disorder.

Precision

Closeness of repeated measurements to each other; reproducibility.

Accuracy

Closeness of a measured value to the true value; validity.