"The secret of life is not to do what you like, but to like what you do."

1. ORGANIZATION AND CHARACTERSTICS OF VIRUSES
BARKATULLAH UNIVERSITY
BHOPAL
PRESENTED
BY
MUHAMMAD ASIF KANTH
SUBMITTED TO :-
DEPARTMENT OF ZOOLOGY AND APPLIED AQUACULTURE
M.SC IV SEM

2. VIRUS is either DNA or RNA, that is protected by a protein coat
called a CAPSID.
Viruses:A
• are noncellular or Acellular
infectious agents
Virology:
• study of viruses
Virologists:
• scientists who study viruses
VIRUS:

3. The concept of a virus as an organism
challenges the way we define life:
* Viruses do not breathe.
* Viruses do not metabolize.
* Viruses do not grow.
* However, they do reproduce.
ASIF KANTH

4. General features of Viruses
Viruses are infectious agents with both living
and nonliving characteristics.
1. Living characteristics of viruses
a. They reproduce at a fantastic rate, but only
in living host cells.
b. They can mutate.

5. …General features of Viruses
2. Nonliving characteristics of viruses
 They are acellular, that is, they contain no
cytoplasm or cellular organelles.
 They carry out no metabolism on their own
and must replicate using the host cell's
metabolic machinery.

6. GENERAL FEATURES OF VIRUSES
 Virus particles contains either DNA or
RNA (not both)
Nucleic Acid is surrounded or coated by
a protein shell (capsid)
Some viruses possess a membrane-like
envelope surrounding the particle

7. …General Properties of viruses
Consists of ≥1 molecule of DNA or RNA
enclosed in coat of protein
May have additional layers
Cannot reproduce independent of living
cells nor carry out cell division as
procaryotes and eucaryotes do
 An intact viral particle is called a virion.

8. Replication Phases
V - Release
- Assembly of virus
DNA and protein
coat into whole
new viruses
- Leaving the cell
ASIF KANTH M.SC IV SEM
Phase I
Phase II
Phase IV Phase VPhase III
I, II, III - Viruses enter cell
- Attachment to cell membrane
- Penetration inside cell
- Losing virus protein coat
IV - Replication
- Tricks cell into making
more viral DNA
- Tricks cell into
making viral protein
coat

9. Viruses Can Help Cells, Too
- Since viruses can transport DNA and RNA
into cells, scientists are exploring Gene
Therapy
- In Gene Therapy, viral genetic material is
replaced with new DNA
- In time, this could be used to cure genetic
diseases. Currently we have no cure for these
types of illnesses

10. DISEASE VIRUSES
AIDS HIV
Wart
Herpes Simplex
Virus
Flu Influenza
Measles Morbillivirus .
Cancer Hepatitis B
ASIF KANTH
Examples of some viral diseases:

11. The Size and Morphology of
Selected Viruses
11

12. Generalized Structure of Viruses
Viral components
Nucleic acids
Capsid
Envelope
12

13. …Generalized Structure of Viruses

14. The Structure of Viruses
Virion size range is ~10-400 nm
All virions contain a nucleocapsid which is
composed of nucleic acid (DNA or RNA) and
a protein coat (capsid)
Some viruses consist only of a nucleocapsid,
others have additional components
Envelopes
 virions having envelopes = enveloped
viruses
 virions lacking envelopes = naked viruses

15. VIRAL ENVELOPES
• Many viruses that infect humans and
other animals are enveloped.
• Envelopes form when viral glycoproteins
and oligosaccharides associate with the
plasma membrane of the host cell.
• All envelopes have a phospholipid
bilayer.

16. The End! And Review
Viruses are very simple: a shell containing
either DNA or RNA.
They infect by hijacking cells’ machinery to
force them to make more viruses.
Viruses are tiny, even compared to a cell.
Some viruses may prove useful in gene
therapy as natural carriers of DNA that was
specially designed to be good for a particular
reason.