Viruses are microscopic parasites that cannot reproduce outside of a host cell. They contain either DNA or RNA as their genetic material. When a virus infects a susceptible host cell, it directs the cell to produce more viruses. The simplest viruses contain only the genetic material and protein coating, while more complex viruses can encode up to 200 proteins. Tobacco mosaic virus was the first virus studied by Wendell Stanley. Viruses are classified based on their genetic material as DNA or RNA viruses, with RNA viruses including notable human diseases like influenza, SARS, and COVID-19.

1. What is a virus?

2. Viruses are microscopic parasites, generally
much smaller than bacteria. They lack the
capacity to thrive(Grow & develop) and
reproduce outside of a host body.

3. Once it infects a susceptible cell, however, a
virus can direct the cell machinery to produce
more viruses.

4. Most viruses have either RNA or DNA as their
genetic material. The nucleic acid may be single-
or double-stranded.

5. The entire infectious virus particle, called a
virion, consists of the nucleic acid and an
outer shell of protein. The simplest viruses
contain only enough RNA or DNA to encode
for proteins.
The most complex can encode 100 – 200
proteins.

6. First Studied virus was TMV (Tobacco Mosaic
Virus) a plant virus by Wendell Stanley
Tobacco Mosaic Virus Wendell Stanley

7. Types of Virus:-
Tobacco Mosaic Virus
HIV An Animal Virus
Animal Viruses
BacteriophagesPlant Viruses
A Bacteriophage

8. On the basis of Genetic material,
Viruses can be grouped as:-

9. DNA Virus RNA Virus&

10. DNA Virus

11. DNA viruses have DNA (Deoxyribose Nucleic Acid). DNA
viruses can be divided into two classes:
•Single-strand DNA viruses
•Double-strand DNA viruses.
*Parvoviruses are the only virus family with a single-
strand DNA genome among the animal viruses.
DNA Virus
Herpes Virus
Hepadna
Virus

12. In contrast, double-strand DNA viruses can be subdivided
into three groups:
(1) those with a small size DNA genome (<10 kb), such as
polyomaviruses and papillomaviruses;
(2) those with a medium size DNA genome (ca., 35 kb),
such as adenoviruses; and
(3) those with a large size DNA genome (ca., 150–250 kb),
such as herpesviruses.
DNA Virus
Adeno Virus
Pox
Virus

13. If u want to remember name of some important DNA
viruses then have a look at this. 👇🏻
An interesting trick to
remember DNA Viruses
(H) A (P) P Y
2 2

14. (H) A (P) P Y2 2
Here, on splitting (H) A (P) P Y we get:- H H A P P Y
H- Herpes virus
H- Hepadna virus
A- Adeno virus
P- Pepo virus
P- Pox virus
2 2

15. RNA Virus

16. RNA Virus
•RNA viruses have RNA (Ribonucleic Acid).
•This nucleic acid is usually single-stranded RNA
(ssRNA) but may be double-stranded RNA (dsRNA).
•Another term for RNA viruses that explicitly excludes
retroviruses is ribovirus
•Notable human diseases caused by RNA viruses
include- Ebola virus disease, SARS, SARS-CoV-2, CoViD-19
rabies, common cold, influenza, hepatitis C, hepatitis E,
West Nile fever, polio and measles, etc..
Corona Virus
Ebola Virus

17. RNA Virus
•The International Committee on Taxonomy of Viruses (ICTV)
classifies
RNA viruses as those that belong to Group III, Group IV or Group V
of
the Baltimore classification system of classifying viruses and does
not consider viruses with DNA intermediates in their life cycle as RNA
viruses.
•Viruses with RNA as their genetic material which also include DNA
intermediates in their replication cycle are called retroviruses, and
comprise Group VI of the Baltimore classification. Notable human
retroviruses include HIV-1 and HIV-2, the cause of the disease AIDS.

18. How Viruses infects
Host Cell?

19. Viral Infection or Lysogenic
cycle of a virus.

20. Thank You

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