Transcript Prions and Viroids

The tiny, not-so-cute guys that you
don’t see coming!
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How they were
discovered:
Far to go:
First observed in
degenerative disease
Kuru. Discovered and
coined by Prusiner 1982.
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Not much is actually
know about prions.
Questions such as how
do they “replicate” are
still unanswered.
Examples of diseases
caused by prions:
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Prions cause
neurodegenerative
diseases such as: kuru,
Creutzfeldt-Jakob, scrapie,
and “Mad Cows Disease.”
Their structure:
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A prion is a protein found
mainly in the brain. It is
not the protein itself that
causes disease but only
the abnormally folded
version of the prion
protein also know as an
infectious prion.
How they work:
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The infectious prion is
somehow capable of
inducing of prion
proteins to adopt an
abnormal configuration.
These abnormal proteins
cannot be destroyed by
lysosomes and they
accumulate to cause cell
and spongy
degeneration of the
brain.
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Discovery:
Classification:
Considered a major
biological breakthrough
when discovered by
pathologist, Diener, 1971.
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Viroids have been
classified into two
families, three subfamilies, and eight genus
and species groups.
There are still many
unclassified viroids.
Diseases caused by
viroids:
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Viroids are primarily
associated with plants.
Viroids are responsible
for crop diseases such as
potato spindle tuber,
avocado sunblotch, etc.
Recently however, it is
found that a certain type
of viroid plays a role in
human hepatitis D.
Structure:

Viroids are 80 times
smaller than normal
viruses; formed without a
protein coat. Contains
short circular RNA
strands, but does not
encode for any protein
products in their
structures.
How they work:
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When a viroid enters the
host cell it takes over
RNA polymerase and
produces copies of itself.
In this manner it can
quickly spread and
grows to numerous
numbers within a cell
before breaking out and
spreading to other cells.
Pictures In order:
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http://www.nickcampos.com
http://student.biology.arizona.edu
http://pubs.acs.org
http://plantdiseasehandbook.tamu.edu
http://schaechter.asmblog.org
http://thevirologyblog.blogspot.ca
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http://www.atsu.edu/faculty/chamberlain/Website/Lects/PRIONS.HTM
http://www.els.net/WileyCDA/ElsArticle/refId-a0000434.html
Text Reference
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Audesirk T., Audeesirk G., Byers B. 2008, Pearson Prentice Hall, Pearson
Education, Inc, Upper Saddle River, NJ Biology Life on Earth with Physiology
pp381-385.
http://mcmanuslab.ucsf.edu
http://www.cdc.gov
http://www.news-medical.net