What is virus History of viruses Virus components How viruses act on genetic material Basic principles What is cancer TWO BASIC MECHANISMS Normal cell cycle ONCOGENES AND TUMOR SUPPRESSORGENES CONTROL THE CELL CYCLE Proto ontogenesis and normal cell division CONCEPT OF ONCOGENES

1. Represented by:Rabia Shehzadi
Roll num.17130814-012
REPRESENTED TO: DR.SADIA ROSHAN
VIRUSES AND VIRAL DISEASES

2. 1. Viruses are responsible for 20% of malignant conditions in
humans, including some of the most common cancers
worldwide, and are especially common in immunosuppressed
patients.
2. The identification of viruses associated with cancers may
provide prognostic information or alternative treatments.
3. Moreover, vaccines are now available for two classes of viruses
that are associated with cancer: hepatitis B virus and human
papilloma viruses (HPV).With new molecular approaches for
virus discovery, the number of cancers that can be linked to
viruses with certainty will grow in the next few years.

3. What is virus
A virus is a small infectious agent that can replicate only inside the
living cells of an organism.
Viruses can infect all types of organisms, from animals and plants to
bacteria and archaea.About 5,000 viruses have been described in
detail, although there are millions of different types.
Viruses are found in almost every ecosystem on Earth and are the
most abundant type of biological entity.

4. Virus particles (known as virions) consist of two or three parts the
genetic material made from either DNA or RNA, ii) a protein coat
that protects these genes; and in some cases iii) an envelope of lipids
that surrounds the protein coat when they are outside a cell.

5. History of viruses
Viruses initially isolated in 1898 as miniscule infectious microbes
that caused plant diseases.
In 1909 Karl Land Steiner implicated a virus as the cause of Polio.
By the early 1920-s the viruses that caused cowpox and herpes had
been isolated and grown in culture
Jenner and Shown inoculation with cowpox prevent small pox.

6. Virus components

7. How viruses act on genetic material
Termin showed that certain tumour viruses carried the enzymatic
ability to reverse the flow of information from RNA back to DNA
using reverse transcriptase.

9. Basic principles
Cancer is a disease of damaged genes. Chemicals and radiation directly damage the genes (the
DNA) of cells that result in
the loss of control of cell division.
Viruses damage/alter the genes of cells
by bringing new genes into the cell that
result in the loss of control of cell
division.

10. What is cancer
Cancer is unregulatedgrowth of cells.
Wound healing is regulatedgrowth of
cells.
Why does unregulated growth occur?

11. TWO BASIC MECHANISMS
What causes cells to lose control of cell
division?
1. Mutations in the genes that encode the
proteins that regulate cell division. The altered
proteins lose their ability to regulate cell
division.
2. Infection of a cell by a virus. The virus brings
new genes into the cell that encode proteins
that alter/inhibit the proteins that regulate cell
division.

12. Normal cell cycle

13. ONCOGENES AND TUMOR SUPPRESSOR
GENES CONTROL THE CELL CYCLE

14. Proto ontogenesis and normal cell
division

15. CONCEPT OF ONCOGENES

16. WHAT IS NORMAL FUNCTION OF PROTOONCOGENES
AND TUMOR SUPPRESSOR GENES?
Most of the proto-oncogenes encode either
growth factors such as epidermal growth
factor (EGF) or are kinasessuch as tyrosine
kinase. The latter are regulators of the cell
cycle.
One of the tumor suppressor genes (RB)
encodes a protein that inhibits E2F, a
transcription factor required for the cell cycle.

17. HOW DO VIRUSES CAUSE CANCER?
Viruses bring new genes into the cell.
Viral genes act in either of two ways:
1. Viral genes encode proteins that activate the cell
cycle to drive the cell into continuous cell division.
(”Foot on the accelerator” model)
2. Viral genes encode proteins that act as inhibitors
of tumor suppressor proteins. (”Foot off the brake”
model)
End result is loss of control of the proteins that
regulate the cell cycle

18. IMPORTANT HUMAN CANCER VIRUSES

19. IMPORTANT HUMAN CANCER
VIRUSES
Human T-cell leukemia virus is a member of the
Retrovirus family (RNA genome)
Epstein-Barr virus and Kaposi’s sarcoma virus are
members of the Herpesvirus family (DNA genome)
Human papilloma virus is a member of the
Papillomavirusfamily (DNA genome)
Hepatitis B virus is a member of the Hepadnavirus
family (DNA genome)
Hepatitis C virus is a member of the Flavivirus
family (RNA genome)

20. VIRAL DNA ENTERS HUMAN DNA

21. HOW RETROVIRUSES CAUSE CANCER:
TRANSDUCTION OF CELLULAR ONCOGENE

22. ONCOGENES AND TUMOR SUPPRESSOR
GENES CONTROL THE CELL CYCLE

23. Tumor suppressor genes

24. Tumor suppressor genes act like a brake
pedal

25. Vaccine against HPV

26. TWO SUCCESSFUL VACCINES
AGAINST HUMAN CANCER
HPV vaccine - protects against cervical,
penile, and anal cancer
HBV vaccine - protects against liver
cancer, the most common cancer worldwide