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Viruses
1.
2. WHAT NOT TO BEWHAT NOT TO BE
STUDIED TODAYSTUDIED TODAY
COMPUTER VIRUS VIRU Sahastrabuddhe
3.
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
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
12.
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
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
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
Editor's Notes
What is a virus
“Sub microscopic entities 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.”[1]
The key features of this definition are as follows:
Single type of nucleic acid – either DNA or RNA but not both
Replication of the virus only with a living cell – they are obligate intracellular parasites.
These characteristics are typical for ALL viruses whether they infect bacteria, plants or animals. [1] Adapted from Collins English Dictionary
Respiratory aerosoles can be generated from the respiratory tract by various means – from speaking to sneezing.
During a sneeze, millions of tiny droplets of water and mucus are expelled at about 200 miles per hour (100 metres per second). The droplets initially are about 10-100 micrometres diameter, but they dry rapidly to droplet nuclei of 1-4 micrometres, containing virus particles or bacteria. This is a major means of transmission of several diseases of humans.
As with many infections viruses can be transmitted between susceptible individuals by a variety of means. The details provided related mainly to viruses infecting humans.
Many animal viruses do not remain infectious for very long outside the host.
Respiratory: Influenza A virus (and rhinovirus). Transmission in the form of aerosols during coughing and sneezing. The viruses are fairly sensitive to drying and their transmission is highest when individuals are in close contact.
Faecal-oral: Enteroviruses (e.g. poliovirus) A lot of viruses are excreted in faeces following high levels of replication in the gut.
Blood borne: Hepatitis B (and HIV). Transferred through contaminated blood products or via shared needles with drug abuse.
Sexual transmission: (HIV)
Animal/insect vector: Rabies. In many instances the virus infection is a specific pathogen of the animal and is not normally transmitted to humans by any other means.
