Biology · Biological Classification · NEET
No. A prion has NEITHER DNA nor RNA. It is made of protein only. This is the most tested point in NEET. Remember: a virus has nucleic acid (DNA or RNA) plus a protein coat, a viroid has free RNA only, and a prion has protein only. So a prion is the one agent with no genetic material at all.
A viroid is free RNA with no protein coat (it causes plant diseases like potato spindle tuber disease). A prion is an abnormally folded protein with no nucleic acid (it causes mad cow disease). Easy memory: viroID = RNA (has 'genetic' info), pRIOn = PROtein. Do not swap them; NEET loves to test this exact mix-up.
Mad cow disease is caused by a prion, which is an abnormally folded protein. NEET has asked this directly in 2019 and again in 2026. If the options include 'abnormally folded protein', that is the answer. Mad cow disease is also called bovine spongiform encephalopathy (BSE). The human version is Creutzfeldt-Jakob disease.
The prion protein is a copy of a normal brain protein but it is folded the wrong way. When this wrongly folded prion touches normal proteins, it forces them to also fold wrongly. This chain reaction spreads and damages the brain, making it spongy (full of holes). So the prion 'multiplies' by changing shape of normal proteins, not by copying genes.
Prions are considered non-living infectious agents, like viruses and viroids. They cannot carry out life processes on their own and only 'work' inside a host. For NEET, just remember prions are grouped with the acellular infectious agents (viruses, viroids, prions) at the end of the Biological Classification chapter.
NCERT says: prions consist of abnormally folded proteins, and this abnormally folded protein causes mad cow disease in animals and a similar disease (Cr-Jakob disease) in humans. This exact line was tested as a 'correct statement' in NEET 2019.
Mad cow disease in cattle is caused by an organism which has:
Mad cow disease is caused by _______.
Which of the following statements is incorrect?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Stanley Prusiner proposed prions and won the Nobel Prize for this work. NCERT does not stress the name, but it helps you remember that prion = protein-only infectious agent.
BSE (bovine spongiform encephalopathy) is the scientific name for mad cow disease in cattle. Creutzfeldt-Jakob disease (Cr-Jakob disease) is the very similar prion disease in humans. Both damage the brain.
No. A protein coat (capsid) is a virus feature that protects the genetic material inside. A prion has no genetic material and is simply the protein itself, so the term 'protein coat' does not apply to it.
Prions are proteins folded in a very stable, abnormal way. They resist heat and normal sterilisation that would kill bacteria or viruses. NEET rarely asks this, but it explains why mad cow disease was hard to control.
No. A virus has nucleic acid (DNA or RNA) plus a protein coat, while a prion is protein only with no nucleic acid. They are two different acellular infectious agents in the NCERT chapter.
