Posted: July 13, 2011 in Uncategorized

What is viruses ?

Viruses are acellular organisms without organelles, cannot independently perform metabolic activities and reproduce themselves, and require other organism cells to live within.

History of viruses discovery

¢In 1883, Adolf Meyer (Germany) observed a disease causing yellow spots on tobacco leaves, he concluded that the cause was an organism which was smaller than bacteria.
¢In 1893, Dimitry Ivanowysky (Russian) → he concluded that the organism caused tobacco disease was pathogenic bacteria and produced toxic compounds.
¢In 1897, M.W. Beijerinck (Dutch) → he concluded that organism causing the tobacco disease could only reproduced themselves in the living organisms.
¢In 1935, Wendell Stanley (USA) → TMV (Tobacco Mosaic Viruses) which was contained protein and nucleic acid.
Characteristics of viruses

1. Size of body is within the range of  0,02 – 0,3 μm and the biggest size is about 200 nm.

2. Consists of nucleic acid (DNA or RNA) surrounded by a protein coat (capsid).

3. Have various shape, such as polyhedral, filament,

T-shape, and bacilli.

4. Can be either inside the cell or outside the cell (as chemical substances).

5. Can reproduce themselves within living cell only.

6. Stable at pH 5.0 to 9.0.

7. Can be freed by ultraviolet and X-rays.

8. Can acts as disease agents.

9. Can act as genetic agents .

Viruses structure

Outside : Capsid (protein)  and Lipoprotein sheath (not all viruses have it)
Inside : Nucleic acid molecules and Various protein (enzymes)
¢Capsid is a virus coat that consists of subunit protein → capsomer. Capsid plays roles in protecting nucleic acid, determining the types of cell that will be attached by virion, and help viruses inserting their virion into host cells.
¢Lipoprotein layer functions in producing viruses genetic materials.
¢The inside of virion consists of one type of material genetic, DNA (deoxyribonucleic acid) or RNA (ribonucleic acid).
Viruses reproduction
¢Lytic cycle → virulent

a. Adsorption and Penetration Stage

→ the virus typically attaches to a specific receptor found on host cell surface, this step is followed by penetrating the viral (material genetic DNA or RNA into host cytoplasm. Virus releases lysosim enzyme to hydrolysis host cell.

b. Replication Stage

→ viral material uses the metabolic machinery of host cells to replicate its own viral particles and arrange virus coat. New viruses being reproduced within host cell.

c. Lysis Stage

→ new viruses destroy (lyses) cell wall of host cell. Once released, the viruses infect other host cells.

¢Lysogenic cycle → temperate virus

a. Adsorption and Penetration Stage

→ viruses attached to host cell and their genetic materials into host cells cytoplasm.

b. Gene Insertion Stage

→ viral genetic material is inserted into host cells DNA, performing provirus. Host cell inserted is called profage.

c. Division Stage

→ provirus replicates itself following host cell replication. On suitable environment, mature provirus will enter to lytic cycle.

Diversity of viruses

a. Based on the types of infected host cell

1. Animal Viruses, such as : rabies viruses, NCD viruses, mouth and nail viruses.

2. Plant Viruses, such as : CVPD viruses, PYDV, TMV, tungro viruses, pox viruses.

3. Human Viruses, such as : HIV, hepatitis virus, herpes virus, DHF virus, chickenpox virus.

4. Bacterial Viruses, such as : bacteriophage.

b. Based on the types of material genetic

1. DNA viruses, such as : bacteriophage, adenovirus, herpes virus.

2. RNA viruses, such as : HIV, polio viruses, rabies viruses, influenza viruses.

Ways of disease transmission by viruses

¢Direct transmission via direct contact or tools they use.
¢Transmission via digestive tract (foods and drinks).
¢Transmission via animal vektor.
The best prevention from virus transmission
¢Natural preventation way is done by antibody.
¢Human-made preventation way is done by vaccine to healthy people.
¢Building suitable houses in which ultraviolet radiation can pass through inside and inactive the viruses.
  1. citra X5 says:

    pak besok kelas X5 memulai materi baru apa masih ditahap pengumpulan LKS … ?? materi selanjutnya tentang archaebacteria , eubcteria khan pak ???

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