* <spoiler text="What toxins are involved in the pathogenesis of diphtheria?">C. diphtheriae has only one toxin, which is encoded by a lysogenic phage. Thus, C. diphtheriae cannot cause diphtheria unless the phage first infects the bacteria and provides it with the DNA necessary for production of the toxin.</spoiler>

* <spoiler text="How does diphtheria toxin cause cell killing?">The toxin is composed of fragment B that attaches to host cells and fragment A which is linked to fragment B by a disulfide bridge. Bound diphtheria toxin enters the acidic endosome of cells, fuses with the endosomal membrane, and then enters the cell cytoplasm. There the disulfide bond of the toxin is broken, releasing the enzymatically active fragment A which then catalyzes the covalent transfer of adenosine diphosphate ribose (ADPR) from nicotinamide-adenine dinucleotide (NAD) to EF-2. EF-2, a ribosomal elongation factor necessary for protein synthesis, is thus inactivated. One molecule of diphtheria toxin can kill a cell by ADP-ribosylating more than a million EF-2 molecules.</spoiler>

{{IPLab 9}}

[[Category: IPLab:Lab 9]]