Replication is the duplication process by which a DNA molecule produces exact copies of itself. Retroviruses are enveloped animal RNA viruses that consist of particles about 100nm in diameter containing a dsRNA genome organized with coding regions flanked by untranslated regions. Adenoviruses are medium-sized non-enveloped viruses containing a dsDNA genome that causes respiratory, eye, and intestinal infections. Viroids are the smallest known infectious agents, naked circular RNA molecules without capsids that infect only plants and require host RNA polymerase to replicate. Prions are infectious agents composed solely of misfolded protein that can propagate without nucleic acids and cause fatal neurological diseases by converting the normal form of the prion protein into an abnormal

2. REPLICATION
Replication is the is the duplication process by which
a DNA molecule produce exact copies of its own
organism.

3. EXAMPLE OF REPLICATION

4. RETROVIRUS
Retroviruses are enveloped animal RNA
viruses.Retroviruses consist of enveloped particles
about 100 nm in diameter.

5. GENOME STRUCTURE
Retroviruses are dsRNA virus. The retroviral genome
is organized with internally located coding regions
flanked by 5 and 3’ untranslated regions. which
function in viral replication . The RNA genome is
7000–10,000 Nucleotides long.

7. Steps
 Adhesion
 Internalization
 Reverse transcription
 Integration
 Assembly
 Release

10. ADENOVIRUS
Discover:-
Adenoviruses were first discovered
in 1953 by “Wallace Rowe” & his
colleagues.
Adenoviruses are medium-sized (90–100nm) , non developed virus
containing a double stranded DNA genome. Their name derives from
their initial isolation from human adenoids in 1953.They Cause
respiratory, eye, and intestinal infections

11. GENOME STRUCTURE
The adenovirus genome is linear, dsDNA have 26 and
48 kbp Adenovirus replication is a protein-primed
process that occurs in the nucleus .Although this is
larger than other viruses in its baltimore group. DNA
replication process finished in 40 h, an infected cell
produces approximately one million copies of viral
DNA.

13.  Adhesion
 internalization
 Transcription & Viral genome replication
 assemply
 Release

17. VIROIDS
Viroids are among smallest infectious molecule.
They are only larger than prions. They are cause over
20 plant diseases.About 30 distinct viroids have been
identified.
Naked RNA molecules
VIROIDS No capsid
No coatings

18. Discover:-
“Theodor Otto Diener” is an american
plant pathologist agriculture research
service in maryland in 1971and
discover the virods.

19.  They are too small to encode for even a single enzyme
 Don’t know how they cause disease
They infect only plants :
EXAMPLE:
 tomatoes
 potatoes
 cucumbers
 citrus trees
 chrysanthemums

20. The first viroid was identified was the
potato spindle tuber viroid [PSTVd.]

21. Animal disease
But, they may be involved in animal diseases like:
 arthritis
 encephalopathies
 cancerous lymphomas

22. GENOME STRUCTURE
viroids are circular ssRNAs about 250-370 nuclotides
long.Viroid genome are extremely small in size .It
affect only plants. requires host cell DNA-dependent
RNA polymerase to replicate.

23. A
type
• A SYMMETRIC
ROLLING
CIRCLE
MECHANISM
B
type
• SYMMETRIC
ROLLING
CIRCLE
MECHANISM

25. PRION
Prions are infectious agent that can replicate without
genetic material. They are also called
 Proteinaceous particle
 Slow viruses
They are self-propagating misfolded conformer protein that
is responsible for a number of disease that affect the brain
and other neural tissue.

26. Discovery:-
“Stanley Benjamin Prusiner” is
an American neurologist and chemist
he won the novel prize In 1997.

27. GENOME STRUCTURE
prpC prpSC
They have no
nucleic acids, it is
a product of a
human gene,
termed the PRNP
gene, found on
chromosome 20.
This gene contains
two exons
separated by a
single intron.

28. Prions cause “8” known animal diseases all 8 are
neurological diseases.
They are,
 Mental derangement
 Loss of muscle control
 Progressive and fatal etc..

29. Other diseases :
 Eg. Kuru
Is an incurable degenerative neurological disorder,
caused by a prion found in humans.

30.  A newly discovered prion disease attacks the PNS
rather than the brain causing
 Chronic diarrhea.

31. some evidence prions may be involved in:
Parkinsons disease
Alzheimers disease
Huntington’s disease

32.  PrPC (prion protein) is present in
“normal” form but, their
abnormal form of prion protein is
PrPSc.
 Newly produced PrPSc molecules
convert more normal molecules to
the abnormal form through
unknown mechanism.

33. Neural Loss :
 Evidence suggests that PrPC must be present for
neural degeneration to occur
 Interaction of PrPSc with PrPC may cause PrPC to
crosslink and trigger apoptosis
 PrPC conversion causes neuron loss, PrPSc is the
infectious agent

34. All prion caused diseases
 –have no effective treatment
 –result in progressive degeneration of the brain and
eventual death