Viruses are ultra-microscopic, non-cellular agents that can only multiply inside host cells. They contain genetic material such as DNA or RNA encased within a protein coat called a capsid. Some viruses have an outer envelope as well. Viruses infect organisms by injecting their genetic material inside host cells and using the cell's machinery to replicate themselves. They are classified based on their structure, type of nucleic acid, size and shape of capsid, and presence of enzymes or envelope. Viruses can be transmitted between organisms in various ways including mechanically, through vectors like insects or fungi, or vertically through seeds or grafts. They have many applications in fields like molecular biology, biotechnology, and nanotechnology.

1. VIRUSES
By
Nisha Kataria

2.  Virus is a group of ultra-microscopic, non-cellular,
highly infectious agents.
 Multiply only intracellularly (inside the living host
cells) without involving growth and division.
 Outside the host cells they are inert particles .
 They are nucleoproteins having one or more
nucleic acid molecule, either DNA or RNA,
encased in a protective coat of protein or
lipoprotein.
Definition :-

3. General characters of viruses
 All viruses have a capsid or head region that contains its genetic material.
The capsid is made of proteins and glycoproteins.
Some viruses, mostly of the type infecting animals, have a membranous envelope
surrounding their capsid. This allows viruses to penetrate host cells through
membrane fusion.
The virus's genetical material rests inside the capsid; that material can be either
DNA, RNA, or even in some cases a limited number of enzymes.
some viruses, mostly those that infect bacteria, have a tail region.
The tail is an often elaborate protein structure.
It aids in binding to the surface of the host cell and in the introduction of virus
genetic material to the host cell.

4. Structure of virus
Viruses are classified on the basis of structure :
1) Type and size of nucleic acid
2) Size and shape of capsid
3) Lipid envelope surrounding nucleocapsid
4) Enzymes
Envelope –
 Virus posses an outer thin loose covering called envelope.
 Composed of proteins, lipids and carbohydrates.
 Many viruses also develop spikes made of glycoprotein on their
envelopes that help them to attach to specific cell surfaces.
Capsid -
 The capsid is the protein shell that encloses the nucleic acid; with its
enclosed nucleic acid, it is called the nucleocapsid.
 This shell is composed of protein organized in subunits known as
capsomers.

5. ;cc4
Structure of virus continue…
Enzymes –
Only few virus contain certain enzymes . For example,
lysozyme in bacteriophages, reverse transcription in
retrovirus.
Nucleoid-
The nucleic acid present in virus is called nucleoid. The
genetic material of virus is of four types:-
1) Double stranded DNA – Occur in Herpes virus, pox
virus, Hepatitis-B-virus(circular)
2) Single stranded DNA - Occur in coliphage
fd(linear), coliphage f *174(cyclic).
3) Double stranded RNA - Occur in Reo virus , wound
tumour virus.
4) Single stranded RNA - Occur in Tobacco mosaic
virus, polio virus, retrovirus(e.g. HIV)

6. REPRODUCTION

7. Transmission of Plant Viruses:
1. Mechanical Transmission
2. Vegetative and Graft
Transmission
3. Pollen Transmission
4. Seed Transmission
5. Nematode Transmission
6. Fungal Transmission
7. Insect Vector Transmission
8. Dodder Transmission

8. Viruses contain the characteristics of both living and non-living organisms, they are utilized in the field
of Biotechnology research. Applications of Viruses:
•Molecular Biology, Cellular Biology, Molecular genetics, such as DNA replication, transcription, RNA
processing, translation, protein transport, and immunology.
•Virotherapy uses viruses as vectors to treat various diseases, as they can specifically target cells and DNA.
It shows promising use in the treatment of cancer and in gene therapy.
•The viruses represent largest reservoirs of unexplored genetic diversity on Earth. They can be used as
alternative to the antibiotics because of the high level of antibiotic resistance now found in some pathogenic
bacteria.
•Viruses contain protein and this property can be used in production of various proteins such as vaccine
antigens and antibodies.
•In nanotechnology, viruses can be regarded as organic nanoparticles. Because of their size, shape, and
well-defined chemical structures, viruses have been used as templates for organizing materials on the
nanoscale.
ECONOMIC IMPORTANCE OF VIRUS

9. THANK YOU