This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
[{'content': 'Receptor for diphtheria toxin lies at ? \nSelect and explain. \nA. Cell membrane, B. Mucous membrane, C. Nucleus, D. None', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Cell membrane Diphtheria toxin The diphtheria toxin acts by inhibiting protein synthesis. It inhibits polypeptide chain elongation in the presence of nicotinamide adinine dinucleotide (NAD) by inactivating elongation factor, EF - 2. The diphtheria toxin is a protein which consists of two fragments, A and B. Both fragments are necessary for the toxic effect : Fragment A - has enzymatic activity and inhibits protein synthesis by inhibiting the chain elongation by inactivating the elongation factor - 2 (Ef - 2). Fragment B - responsible for binding the toxin to the cells. The toxin binds to specific receptors (HB-EGF receptors) present on susceptible cells and enters by receptor-mediated endocytosis. Toxin has special affinity for ceain tissues such as myocardium, adrenals and nerve endings.", 'role': 'assistant'}]