Prions

 

 Introduction

Prions are infectious proteins that lack nucleic acids (DNA or RNA)

Characteristics of Prions:

1. Prions are infectious proteins without any nucleic acids (DNA or RNA).

2. Discovered by Stanley B. Prusiner in 1982 (Nobel Prize 1997).

3. They are abnormal forms of naturally occurring proteins, capable of inducing other normal proteins to misfold.

4. Prions cause neurodegenerative diseases in animals and humans (e.g., Mad cow disease, Creutzfeldt–Jakob disease).

2. Non-living and Living Characteristics

2.1 Non-living Characteristics

1. Lack nucleic acids, no metabolism, no cell-like features.

2. Do not reproduce independently.

2.2 Living Characteristics

1. Self-propagating misfolded proteins.

2. Resistant to heat and radiation.

3. Cause heritable neurodegenerative diseases.

3. History of Prions

1. 1950s–60s – Kuru disease studied in Papua New Guinea tribes.

2. 1982 – Stanley Prusiner introduced the term 'prion' (proteinaceous infectious particle).

3. 1980s–90s – Recognized as the cause of Mad Cow Disease (BSE) epidemic.

4. Structure

1. Made up of a misfolded protein called PrP^Sc (scrapie form).

2. The normal protein is PrP^C, present in nerve cells.

3. PrP^Sc converts PrP^C into abnormal form, leading to brain damage.

5. Importance

1. Humans: Cause Creutzfeldt–Jakob disease, Kuru, Fatal familial insomnia.

2. Animals: Cause Scrapie (sheep), Bovine Spongiform Encephalopathy (cattle), Chronic wasting disease (deer).

3. Medical importance: Cause incurable, fatal brain diseases.

FAQs on Prions

1. How are prions different from viruses?
 Prions contain only proteins (no nucleic acids), while viruses contain nucleic acids.

2. Why are prion diseases fatal?
Because prions damage brain tissue, leading to progressive neurodegeneration.

3. Why are prions resistant to sterilization?
Prions are abnormally folded proteins that resist heat, chemicals, and radiation.

MCQs on Prions

1. Prions are composed of:
(a) DNA only (b) RNA only (c) Protein only ✅ (d) DNA + RNA

2. The normal cellular form of prion protein is:
(a) PrP^Sc (b) PrP^C ✅ (c) RNA (d) DNA

3. Which of the following is a prion disease in humans?
(a) Scrapie (b) Kuru ✅ (c) Avocado sunblotch (d) Potato spindle tuber

Worksheet

Fill in the blanks:

1. Prions are infectious agents made up of __________.

2. The abnormal prion protein is called __________.

3. The normal cellular form of prion protein is __________.

4. Mad cow disease is caused by __________.