This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Infectious Disease, Subject name: Pathology
Prion includes 
Select and explain. 
A. DNA and RNA, B. Only RNA, C. Proteins, D. Only DNA
C: Proteins
Answer: C: Proteins 
Explanation: Ans. is 'c' i.e. Proteins Prions are infectious proteins that cause degeneration of the central nervous system.They are infectious particles that lack nucleic acid.Prions are composed largely, if not entirely of PrP molecules.Four important points about prions are: -Prions are the only known infectious pathogens that are devoid of nucleic acid, all other infectious assents possess genomes composed of either RNA or DNA that direct the synthesis of their progeny.Prions disease may manifest as infectious, genetic and sporadic disorders; no other group of illness with a single etiology presents with such a wide spectrum of clinical manifestations. Prions disease results from the accumulation of PrPSc the conformation of which differs substantially from that of its precursor PrPc.PrPSc can exist in a variety of different conformations each of which seems to specify a particular disease phenotype.Prions reproduce by binding to the normal cellular isoform of prion protein and stimulating conversion of PrP into the disease causing isoform.