Lebanese University Faculty of Medical Sciences Entrance Examination - Second Year, General Medicine key terms

The passive movement of water across a selectively permeable membrane from a region of lower solute concentration to one of higher solute concentration, driven by a difference in water potential.

The potential energy of water per unit volume, expressed in pressure units; pure water at atmospheric pressure has a value of zero, and water moves spontaneously toward regions of lower water potential.

The ability of an external solution to cause a cell to gain or lose water by osmosis, classified as hypotonic, isotonic, or hypertonic relative to the cytoplasm of the cell.

The substrate concentration at which an enzyme-catalysed reaction proceeds at half its maximum velocity; a low value indicates high affinity of the enzyme for that substrate.

The maximum reaction rate reached when an enzyme is fully saturated with substrate, corresponding to the plateau of the hyperbolic rate-versus-substrate curve.

A reversible reduction in enzyme activity caused by a molecule that binds the active site and competes with the substrate; it raises the apparent Km but leaves Vmax unchanged at high substrate concentration.

Movement of a solute across a membrane against its gradient, powered by the downhill movement of a second solute; the two may travel in the same direction (symport) or opposite directions (antiport).

The mode of DNA copying in which each parental strand serves as a template, so that every daughter double helix contains one original strand and one newly synthesised strand.

A short stretch of DNA synthesised discontinuously on the lagging template strand during replication, later joined into a continuous chain by DNA ligase.

An enzyme that adds deoxyribonucleotides to a growing DNA strand, always extending the new chain in the 5' to 3' direction and requiring a pre-existing primer to begin.

A triplet of consecutive nucleotides in messenger RNA that specifies one amino acid or a stop signal during translation; the genetic code it represents is degenerate and nearly universal.

An insertion or deletion of a number of nucleotides not divisible by three, which shifts the reading frame downstream and usually alters every subsequent amino acid in the protein.

A single base substitution that changes one codon so that a different amino acid is incorporated, potentially altering protein function without necessarily destroying it.

A pattern in which a trait appears only when both copies of a gene carry the variant; carriers with one copy are usually unaffected, and consanguinity raises the risk of affected offspring.

Transmission of a gene located on the X chromosome; recessive variants typically affect males more severely because they carry only one X, while carrier females may show mild features.

The proportion of individuals carrying a particular genotype who actually display the associated phenotype, often expressed as a percentage for a defined population.

The condition in which allele and genotype frequencies in a large, randomly mating population remain constant across generations in the absence of selection, mutation, migration, and genetic drift.

The amount of substance containing exactly Avogadro's number of elementary entities, used to convert between mass in grams and numbers of particles in chemical calculations.

The number of elementary entities in one mole, approximately 6.022 × 10^23 per mole, a constant that links microscopic particle counts to measurable macroscopic quantities.

The mass of one mole of a substance in grams per mole, numerically equal to its relative molecular mass and obtained by summing the atomic masses of its constituent atoms.

A solution that resists large changes in pH when small amounts of acid or base are added, typically made from a weak acid with its conjugate base or a weak base with its conjugate acid.

A logarithmic measure of hydrogen ion activity in a solution, defined as the negative base-10 logarithm of the hydrogen ion concentration in moles per litre.

The stage of a titration at which the amount of titrant added is stoichiometrically equal to the amount of analyte present, not necessarily coinciding with neutrality of the mixture.

The rule that a system at equilibrium responds to a change in conditions, such as concentration, pressure, or temperature, by shifting in the direction that partly counteracts the imposed change.

The ratio of product concentrations to reactant concentrations, each raised to its stoichiometric coefficient, at equilibrium for a given reaction at a stated temperature.

The property of a molecule that is not superimposable on its mirror image, usually arising from a carbon atom bonded to four different groups and giving rise to enantiomers.

One of a pair of stereoisomers that are non-superimposable mirror images of each other and rotate plane-polarised light in opposite directions.

A molecule with the same molecular formula and atom connectivity as another but a different spatial arrangement of atoms, including enantiomers and diastereomers.

A species that donates an electron pair to form a new chemical bond, often an anion or a molecule with a lone pair, and is attracted to electron-poor centres.

A species that accepts an electron pair to form a new bond, typically electron-deficient and attracted to regions of high electron density such as double bonds or lone pairs.

The guidance that in addition of a hydrogen halide to an unsymmetrical alkene, the hydrogen adds to the carbon already bearing more hydrogens, generating the more stable carbocation intermediate.

The relationship stating that the net force on a body equals its mass multiplied by its acceleration, so that a given force produces smaller acceleration for a more massive object.

The energy a body possesses because of its motion, equal to one half of its mass multiplied by the square of its speed, and always non-negative.

The principle that the total momentum of an isolated system remains constant, so that in a collision or explosion the vector sum of momenta before and after is unchanged.

The instantaneous rate of change of a function with respect to a variable, geometrically the slope of the tangent line to its graph at a point.

The value that a function approaches as its input approaches a specified point, which may differ from the value of the function at that point or may not exist.

A mathematical quantity representing accumulated change, interpreted geometrically as the signed area under a curve over an interval and linked to the antiderivative by the fundamental theorem of calculus.

The maintenance of relatively stable internal conditions, such as temperature, pH, and blood glucose, through negative feedback loops that detect and correct deviations from a set point.

A control mechanism in which the output of a system reduces the original stimulus, damping fluctuations and keeping a physiological variable close to its reference value.

A rapid, all-or-none reversal of membrane potential in an excitable cell, produced by sequential opening of sodium and potassium channels and propagated along the axon.

An unmeasured factor that is associated with both the exposure and the outcome, distorting the apparent relationship between them unless controlled by design or analysis.

The comparison group in an experiment that does not receive the treatment under study, allowing investigators to attribute observed differences to the intervention rather than to other influences.

Two measures of a diagnostic test: sensitivity is the proportion of truly affected people correctly identified, while specificity is the proportion of truly unaffected people correctly classified as negative.

The probability that a person with a positive test result actually has the condition, which depends on test characteristics and on how common the condition is in the tested population.

A conclusion that an observed result is unlikely to have arisen by chance alone under a stated null hypothesis, conventionally judged against a preselected threshold such as p < 0.05.

The standard reference posture in which a person stands upright, facing forward, with arms at the sides and palms turned forward, used to describe directions and planes consistently.

The technique of deducing a medical term's meaning from its Greek or Latin components, such as a prefix for location, a root for structure, and a suffix for condition or procedure.