Abnormal protein and their intro

2. ROLL NO: 226
SUBJECT: BOTANY

3. contents
INTRODUCTION
DISCOVERY
STRUCTURE
FORMS
REPLICATION
HISTORY

5. Introduction TO PRIONS
Pronounced as “pree-on”.
Shortened for : PROTANACEOUS
INFECTIOUS PARTICLE
Causes TSE (Transmissible Spongiform
Disease) which attacks the central nervous
system (the brain).
Covered only with protein coat.

6. PRIONS
 Infectious proteins- proteins which cause
disease.
Discovered by PRUSINER in 1982 in SCRAPIE
(neurological disease in sheep).
Prusiner won the Nobel Prize in MEDICINE in
1997
Misfolded proteins in animals which are
pathogenic. Normally folded versions are non-
pathogenic
Causes the similar proteins also to misfold.

8. BASIC
STRUCTURE
Normal prions
contain about
200-250 amino
acids twisted into
a three telephone
chord-like coils
known as
helicles,with tails
of more amino
acids.

9. Basic structure
The mutated and
infectious form is
built from the
same amino acids
but takes a
different shape.
It is folded
abnormally.

11. INTERESTING FACTS!
Prions are extremely resistant to heat and
chemicals.
Prions are very difficult to decompose
biologically, they remain in soil for many
years.
Prions do not contain any nucleic acid, they
don’t have DNA or RNA.
Hundred times smaller than the smallest
known virus.

14. PrP-sen(sensitive)
Both the forms contain exact same string of amino
acids however, the two forms have different
shapes.
PrP-sen is produced by normal healthy cells. This
version is sensitive to being broken down.
It is present mainly in neurons in brain.
Scientists don’t know the exact function of PrP-
sen, but there is evidence that it may be involved
in communication between neurons, cell death
and controlling sleep patterns.

15. PrP-res(resistant)
The second type of prion protein is PrP-res,
is the disease causing form.
Organisms with it develop spongiform
disease.
This form is resistant to being broken down.
Because of their abnormal shape, PrP-res
proteins tend to stick to each other. Over
time, the PrP-res molecules attack up to
form long chains called “amyloid fibres”.

17. REPLICATION
Converts properly folded normal proteins into
infected ones.
Normal form of prions is PrP-sen while infectious is
PrP-res.
PrP-res comes in contact with PrP-sen and convert it
into PrP-res.
These newly formed proteins cause others to convert
and thus start a CHAIN REACTION.
These prions cause other similar proteins to lose
function , cause disease.

24. CONTROVERSY!
DNA and RNA are the only substances now
known to replicate in body tissues, then how
do prions replicate without nucleic acids?
Some believe that TSEs are caused by an
unidentified slow-acting virus.
Others believe a small virus accompanies a
prion and they work together to cause
disease.