What this page covers
Practice Step 1-style biochemistry questions on Diphtheria toxin mechanism (EF-2 ADP-ribosylation), including Unvaccinated child, gray adherent pseudomembrane, bleeding on removal, bull neck, with emphasis on enzyme / mechanism and answer-choice reasoning.
How to use this page
Review the topic and reasoning focus, then practice Step 1-style questions inside BiochemStep. The question set emphasizes mechanism-first answer-choice reasoning rather than passive content review.