Articles

C3 is the central complement amplifier — its deficiency causes broad opsonization failure and susceptibility to encapsulated bacteria like Strep pneumoniae, H.

In Prader-Willi and Angelman syndromes, the child has one intact chromosome 15 from the surviving parent — yet the syndrome still develops in full.

During the HBV window period — when HBsAg has cleared but anti-HBs has not yet appeared — the only detectable serologic marker is anti-HBc IgM.

When a mitochondrial mutation causes one sibling to be bedridden, one to have mild fatigue, and one to be asymptomatic — all three having inherited the same mutation from the same mother — that is heteroplasmy, not variable expressivity.

NK cells kill cells that are missing MHC I.

Pleiotropy and variable expressivity describe different observations about the same mutation, and Step 1 exploits the fact that students confuse them.

Anticipation in myotonic dystrophy can occur through either parent — but the congenital form, which presents at birth with profound hypotonia and respiratory failure, almost exclusively comes from the mother.

Dobutamine is a positive inotrope — it makes the ventricle squeeze harder.

The type of immune defect determines which Candida disease pattern you get.

In septic shock (warm phase), cardiac output is high and SVR is low — the opposite of cardiogenic and hypovolemic shock, where CO is low and SVR is high.

When a patient has Afib confirmed to have started within the past 48 hours, you don't need to wait 3 weeks on anticoagulation, and you don't need a TEE.

When a cord prolapses, C-section is the definitive management — but it is not the first intervention.

In HFrEF, carvedilol reduces mortality — that evidence is solid.

After McRoberts maneuver fails in shoulder dystocia, the next move is suprapubic pressure — not fundal pressure, not C-section.

Aldoses and ketoses differ in where the carbonyl group sits, not in how many carbons they contain.

When the MCAT gives you a disease prevalence for an autosomal recessive condition, you are looking at q² — the frequency of homozygous recessive individuals.

A buffer resists pH change by providing a weak acid and its conjugate base that can react with small amounts of added acid or base.

Unsaturated fats yield less ATP per carbon than saturated fats of the same chain length because their pre-existing double bonds cause one step of beta-oxidation to be skipped per double bond.

A proton leak through the inner mitochondrial membrane collapses the proton gradient before protons reach ATP synthase.

Crossing over occurs in Prophase I because that is the only stage of meiosis when homologous chromosomes are physically paired together.

Lactate fermentation produces zero ATP.

Net ATP from glycolysis is 2, not 4, because glycolysis spends 2 ATP before it makes any.

Osteosarcoma occurs in teenagers, in the metaphysis, and produces an aggressive periosteal reaction — sunburst pattern and Codman's triangle on X-ray.

When ischemia kills tissue in most solid organs — heart, kidney, spleen — the scaffold holds.

A pulmonary embolism causes a red (hemorrhagic) infarct because the lung has two blood supplies.

Histamine causes the immediate vascular leak in acute inflammation.

A tumor is defined as malignant the moment its cells breach the basement membrane into underlying tissue.