The Viroids and Prions

1. VIROIDS AND PRIONS
Presented by
John Avinash. R
I M.Sc. Applied Microbiology

2. Contents
▸ Introduction
▸ Viroids
i. History
ii. Definition
iii. Examples
▸ Prions
i. History
ii.Definition
iii. Examples
▸ Comparison between Viroids and Prions
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3. Introduction
▸ A virus is a non-cellular particle made up of genetic material (DNA) and
protein that can invade living cells.
▸ Beijerinck (1897) coined the Latin name “virus” meaning poison
▸ Basic Characteristics:
*Non living structures
*Non-Cellular
*Have a protein coat called the capsid
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*Have a nucleic acid core containing DNA or RNA
*Capable of reproducing only when inside a HOST cell

4. 1. VIROIDS
Virus - Like

5. i. History
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▸ In 1971, Theodor Diener, a pathologist working at the Agriculture Research
Service, discovered an acellular particle that he named a viroid, meaning
“virus-like.”
▸ Viroids consist only of a short strand of circular RNA capable of self-replication.
▸ The first viroid discovered was found to cause potato tuber spindle disease,
which causes slower sprouting and various deformities in potato plants.

6. Cont. History
6
• Like viruses, potato spindle tuber viroids
(PSTVs) take control of the host
machinery to replicate their
RNA genome.
• Unlike viruses, viroids do not have a
protein coat to protect their genetic
information.

7. 7
▸ Viroids are infectious RNA particle without a Protein
Coat (Major difference between Virus and Viroid)
▸ Viroids are much simpler than viruses.
▸ Structurally, viroids are smaller in size
▸ Comprising single-stranded, circular RNA molecules
having approximately 250-370 nucleotides.
▸ Viroids cannot replicate on their own. (as their RNA
does not encode any gene products.)
ii. Definition:

8. Structure:
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Rod – like Structure
Branched Structure
Single Stranded Circle

9. iii. Examples
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POTATO SPINDLE TUBER VIROID (PSTV)
which is typically spread when infected knives are used to cut healthy potatoes,
which are then planted.

10. Examples
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TOMATO PLANTA MACHO VIROID (TPMVd)
infects tomato plants, which causes loss of chlorophyll, disfigured and brittle leaves, and very
small tomatoes, resulting in loss of productivity in this field crop.

11. Examples
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AVOCADO SUNBLOTCH VIROID (ASBVd)
results in lower yields and poorer-quality fruit.

12. Examples
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PEACH LATENT MOSAIC VIROID (PLMVd)
can cause necrosis of flower buds and branches, and wounding of ripened fruit, which
leads to fungal and bacterial growth in the fruit.

13. Treatment
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Traditional anti-viroid methods have been
employed for treating the infections caused by
these viroids.

14. 2. PRIONS
Misfolded Protein

15. i. History
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▸ In 1982, Stanley Prusiner, a medical doctor studying scrapie (a fatal,
degenerative disease in sheep) discovered that the disease was caused by
proteinaceous infectious particles, or prions.
▸ Earlier the scientists believed that any infectious particle must contain
either DNA or RNA, but Prions proved it wrong.

16. Cont. History
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• Because proteins are acellular and do
not contain DNA or RNA.
• Prusiner’s findings were originally met
with resistance and skepticism;
However, his research was eventually
validated, and he received the Nobel
Prize in Physiology or Medicine in 1997.

17. 17
▸ Prions are “infectious proteins” or “misfolded proteins”
▸ They are normal body proteins that get converted into an
alternate configuration by contact with other prion proteins
▸ They have no DNA or RNA
▸The main protein involved in human and mammalian prion
diseases is called “PrP (Prion Protein)”
▸They are responsible for several neurodegenerative
diseases in mammals. These infectious agents are primarily
composed of sialoglycoprotein – a combination of sialic acid
and glycoprotein and usually lack nucleic acid.
ii. Definition:

18. Structure:
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19. iii. Examples
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CREUTZFELDT-JAKOB DISEASE (CJD)
is a fatal disease that causes degeneration of neural tissue.

20. Examples
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TRANSMISSIBLE SPONGIFORM ENCEPHALOPATHY (TSE)
in animals include mad cow disease, scrapie (in sheep and goats), and chronic wasting
disease (in elk and deer)

21. Treatment
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Currently, there is no treatment or cure for
neurodegenerative diseases because prions are extremely
difficult to destroy as they are resistant to chemicals,
heat, radiation and even standard sterilization procedures.

22. 3. Comparison between
Viroids and Prions

23. a. Definition
Viroids are
infectious RNA
molecules.
Prions are
infectious
protein
particles.
Viroids Prions

24. b. Terminology
Viroids are
“Virus-like”
Particles.
Prions are
“Infectious Protein”
or Misfolded
Protein.”
Viroids Prions

25. c. Size
Viroids are
smaller than
viruses.
Prions are
smaller than the
viroids.
Viroids Prions

26. d. Composition
Viroids are
composed of
single strands
of RNA.
Prions are
composed of
only protein
molecules.
Viroids Prions

27. e. Infections
Viroids Mostly
infect the
Plants.
Prions mainly
causes
neurodegenerative
diseases
in Mammals.
Viroids Prions

28. f. Types of Diseases
▸ Potato Spindle
Tuber Viroid (PSTV)
▸ Tomato Planta
Macho Viroid (TPMVd)
▸ Avocado
Sunblotch Viroid (ASBVd)
▸ Peach Latent Mosaic Viroid
(PLMVd)
▸ Mad cow diseases in cattle
▸ Scrapie in sheep and goats
▸ Creutzfeldt-Jakob disease in
humans
▸ Gerstmann-Straussler-
syndrome in humans
Viroids Prions

29. g. Treatment / Cure
Traditional anti-viroid
methods have been
employed for treating
the infections caused
by these viroids.
Currently, there is no treatment
or cure for neurodegenerative
diseases because prions are
extremely difficult to destroy as
they are resistant to chemicals,
heat, radiation and even standard
sterilization procedures.
Viroids Prions

30. 30
Table of Comparison
Viroids Prions
a. Definition
Viroids are infectious RNA
molecules.
Prions are infectious protein
particles.
b. Terminology Viroids are “Virus-like” Particles.
Prions are “Infectious Protein”
or Misfolded Protein.”
c. Size Viroids are smaller than viruses. Prions are smaller than the viroids.
d. Composition
Viroids are composed of single
strands of RNA.
Prions are composed of only protein
molecules.
e. Infections Viroids Mostly infect the Plants.
Prions mainly
causes neurodegenerative diseases
in Mammals.

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Viroids Prions
f. Types of
Diseases
• Potato Spindle Tuber Viroid (PSTV)
• Tomato Planta
Macho Viroid (TPMVd)
• Avocado Sunblotch Viroid (ASBVd)
• Peach Latent Mosaic Viroid
(PLMVd)
• Mad cow diseases in cattle
• Scrapie in sheep and goats
• Creutzfeldt-Jakob disease in
humans
• Gerstmann-Straussler- syndrome
in humans
g. Treatment /
Cure
Traditional anti-viroid methods have
been employed for treating the
infections caused by these viroids.
Currently, there is no treatment or
cure for neurodegenerative diseases
because prions are extremely
difficult to destroy as they are
resistant to chemicals, heat,
radiation and even standard
sterilization procedures.

32. For doubts and Queries,
Use the Comment Section
THANK
YOU
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