Viruses are submicroscopic entities consisting of nucleic acid surrounded by a protein coat. They are non-cellular and lack the ability to metabolize or reproduce outside of a host cell. Viruses can be classified based on their capsid structure, nucleic acid content, and presence of an envelope. They infect host cells by landing on the surface, attaching to receptors, injecting their nucleic acid, and hijacking the cell's machinery to replicate through lytic or lysogenic cycles. As obligate intracellular parasites, viruses are completely dependent on host cells for replication.

2. WHAT NOT TO BEWHAT NOT TO BE
STUDIED TODAYSTUDIED TODAY
COMPUTER VIRUS VIRU Sahastrabuddhe

4. Sub microscopic entity consisting
of a single nucleic acid surrounded
by a protein coat and capable of
replication only within the living
cells of bacteria, animals or
plants.

5. WHAT AREWHAT ARE
VIRUSES?VIRUSES? IN LATIN, VIRUS MEANS POISON
 VIRUS ARE SUBMICROSOPIC ENTITIES
 THEY ARE NON CELULAR
 VIRUSES LACK PROTEIN SYNTHESIS
MACHINERY
 VERY MUCH DEPENDANT ON HOSTS FOR
THEIR MULTIPLICATION
 MOSTLY HAVE RNA AS THE GENETIC
MATERIAL BUT DNA MAY ALSO BE PRESSENT
IN SOME CASES BUT NOT BOTH.
 THEY ARE INCAPABLE OF METABOLISM
 THEY SHOW NO INCREASE IN SIZE

7. HE, WAS
THE ONE
WHO FIRST
TIME
DISCOVERE
D VIRUS
(TOBACCO
MOSAIC

11. VIRUSES CAN BE CLASSIFIED ON THE
FOLLOWING CRITERIA:
 FORM OF CAPSID:
o HELICAL
o ICOSAHEDRAL
o COMPLEX
 NUCLEIC ACID:
o DNA
o RNA
 PRESENCE OF ENVELOPE
o NAKED
o ENVELOPED

13. IT IS A PROTEIN COAT OF THE VIRUS
COMPRISED OF MONOMERS CALLED
‘CAPSOMERES’

14. THESE ARE SPIKES THAT ARE LOCATED ON THE
CAPSID OR ON ENVELOPE
THESE HELP THE VIRUS TO ATTACH TO THE HOST
CELL
THEY ARE NOT FOUND IN ALL VIRUSES

15. IN SOME VIRUSES, A COVERING OVER THE
NUCLEOCAPSID IS SEEN.
THIS CAPSID IC MADE UP OF LIPOPROTEIN
BILAYER.

16. IT MAY BE COMPRISED OF DNA OR RNA,
MOSTLY- RNA

17. BACTERIOPHAGEBACTERIOPHAGE

18. BACTERIOPHAGE INFECTINGBACTERIOPHAGE INFECTING
BACTERIABACTERIA

19. A VIRUS ATTACKS THE HOST
CELL IN THE FOLLOWING
ORDER:
• LANDINGLANDING
• ATTACHMENTATTACHMENT
• TAIL CONTRACTIONTAIL CONTRACTION
• PENETRATION & UNPLUGGINGPENETRATION & UNPLUGGING
• NUCLEIC ACID INJECTIONNUCLEIC ACID INJECTION
MECHANISM OF VIRALMECHANISM OF VIRAL
ATTACKATTACK

20. LANDINGLANDING

21. ATTACHMENTATTACHMENT

22. TAIL CONTRACTIONTAIL CONTRACTION

23. PENETRATION & UNPLUGGINGPENETRATION & UNPLUGGING

24. NUCLEIC ACID INJECTIONNUCLEIC ACID INJECTION

25. LYTIC CYCLELYTIC CYCLE
VIRUSES REPLICATE THROUGH THE
LYTIC CYCLE. BUT MAY ALSO ENTER
INTO THE LYSOGENIC PHASE.
VIRUSES IN EXTRACELLULAR
CONDITION ARE INACTIVE BUT ONCE
THEY ENTER THE HOST CELL, THEY
BECOME VERY ACTIVE

26. LYTIC CYCLELYTIC CYCLE

27. Respiratory transmission
Influenza A virus
Faecal-oral transmission
Enterovirus
Blood-borne transmission
Hepatitis B virus
Sexual Transmission
HIV
Animal or insect vectors
Rabies virus

28. VIRUSES LACK THE PROTEIN
SYNTHESIS MACHINERY,
HENCE THEY CANNOT
REPLICATE WITHOUT
ABSORBING NUTRIENTS FROM
HOST BODY
THIS IS THE REASON WHY
VIRUSES ARE TERMED AS
OBLIGATE INTRACELLULAR
PARASITES.
REPLICATIONREPLICATION