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

34 cards. Read the term and the definition here. The deck at the top of this page is optional.

Central dogma

The flow of genetic information from DNA to RNA to protein: DNA is transcribed into mRNA, which is translated by ribosomes into a polypeptide chain.

Michaelis constant Km

The substrate concentration at which an enzyme works at half its maximum velocity. A low Km indicates high enzyme affinity for substrate; a high Km indicates low affinity.

Competitive inhibition

An inhibitor competes with substrate for the active site. It raises the apparent Km but leaves Vmax unchanged, because high substrate can outcompete the inhibitor.

Na+/K+-ATPase

A membrane pump that moves three sodium ions out and two potassium ions in per ATP hydrolyzed. It maintains resting membrane potential and cell volume.

Okazaki fragments

Short DNA segments synthesized discontinuously on the lagging strand during replication. DNA ligase later joins them into a continuous strand.

Mendel's law of segregation

The two alleles of a gene separate during meiosis I, so each gamete receives only one allele. Fusion at fertilization restores the pair in the offspring.

Test cross

A cross between an individual showing a dominant phenotype and a homozygous recessive individual. It reveals whether the dominant individual is homozygous or heterozygous.

Hardy–Weinberg equilibrium

Allele and genotype frequencies remain constant across generations when there is no selection, mutation, migration, genetic drift, or non-random mating. Expressed as p² + 2pq + q² = 1.

Codominance

A condition in which both alleles are fully expressed in the heterozygote, producing a combined phenotype. Human AB blood type is the classic example.

X-linked recessive inheritance

A pattern where the gene lies on the X chromosome. Males are affected more often; affected fathers transmit the allele to all daughters but no sons.

pH definition

The negative base-10 logarithm of hydrogen ion concentration: pH = −log[H⁺]. At 25 °C, pH + pOH = 14, and pH 7 is neutral.

Henderson–Hasselbalch equation

pH = pKa + log([A⁻]/[HA]). It describes buffer behavior and shows that buffer capacity is greatest when the solution pH equals the pKa.

Limiting reagent

The reactant that is fully consumed first in a chemical reaction and therefore determines the maximum amount of product formed, based on stoichiometry.

Le Chatelier's principle

When a system at equilibrium is disturbed by a change in concentration, pressure, or temperature, the equilibrium shifts to counteract that change.

Markovnikov's rule

In addition of HX to an alkene, hydrogen adds to the carbon with more hydrogens, giving the more stable carbocation intermediate. Peroxides reverse this selectivity.

SN1 versus SN2

SN1 is a two-step substitution via a carbocation, favored by tertiary substrates and polar protic solvents. SN2 is one concerted step, favored by primary substrates.

Chirality

A property of a molecule that is not superimposable on its mirror image. It usually requires a carbon with four different groups attached.

Hückel's aromaticity rule

A cyclic, planar, fully conjugated molecule with 4n + 2 pi electrons is aromatic. Benzene has six pi electrons and undergoes substitution rather than addition.

Ohm's law

The current through a conductor equals the voltage across it divided by its resistance: V = IR. Power dissipated is P = VI = I²R.

Snell's law

For light crossing an interface, n₁sinθ₁ = n₂sinθ₂. It predicts bending toward the normal when entering a denser medium.

Conservation of momentum

In an isolated system with no external force, total momentum before an interaction equals total momentum after. Kinetic energy is conserved only in elastic collisions.

Quadratic formula

For ax² + bx + c = 0, the roots are x = (−b ± √(b² − 4ac))/(2a). The discriminant b² − 4ac determines the number of real roots.

Chain rule

The derivative of a composite function f(g(x)) equals f'(g(x)) multiplied by g'(x). It is the key rule for differentiating nested functions.

Logarithm product rule

log(ab) = log a + log b. Related rules are log(a/b) = log a − log b and log(aⁿ) = n log a, useful for solving exponential equations.

Cardiac output

The volume of blood pumped by one ventricle per minute, equal to heart rate multiplied by stroke volume. Normal resting value is about 5 litres per minute.

Bohr effect

A rightward shift of the oxygen–hemoglobin dissociation curve caused by increased CO2, H⁺, temperature, or 2,3-BPG, which lowers hemoglobin's oxygen affinity.

Nephron reabsorption

The process by which the kidney returns filtered water and solutes to the blood. Most glucose and amino acids are reabsorbed in the proximal tubule.

Action potential phases

Depolarization from sodium influx, repolarization from potassium efflux, and hyperpolarization. The Na+/K+ pump later restores the original ion gradients.

Sensitivity and specificity

Sensitivity is the proportion of true cases correctly identified. Specificity is the proportion of non-cases correctly identified as negative.

Correlation versus causation

Correlation means two variables change together; causation means one produces the other. A confounding variable can create a correlation without causation.

p-value

The probability of observing data at least as extreme as the study data, assuming the null hypothesis is true. It is not the probability that the null is true.

Anatomical position

The reference posture with the body upright, face forward, arms at the sides, and palms facing forward. Directional terms such as medial and proximal are defined relative to it.

Medical suffix -itis

A suffix meaning inflammation, as in arthritis (joint inflammation) or hepatitis (liver inflammation). It is distinct from -osis, which denotes a condition or degeneration.

Precision versus accuracy

Precision is how closely repeated measurements agree with each other. Accuracy is how close a measurement is to the true value; a measure can be precise but inaccurate.