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Curriculum of cambridge

international examinations( igcse ) ktsp

INTRODUCTION,

CHARATERISTIC ANDREPRODUCTION OF VIRUS

VIR

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VIR

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1.1.IRENA LUCYIRENA LUCY2.2.GITA YULIA SARIGITA YULIA SARI3.3.HENDI AVIANO PHENDI AVIANO P4.4.SAMUEL PIRDIONSAMUEL PIRDION

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LEARNING OUTCOMELEARNING OUTCOME

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MATERIALMATERIAL

INTRODUCTIONINTRODUCTIONqVirus is the latin word for toxin.

qVirus history began when a man named A.Mayer, a German scientist, discovered one in 1883. His

research was on the cause ofTobacco mosaicdisease.

qMayers hypotesis was tasted by a Russian scientistnamed Dmitri Iwanowski in 1892.

qSix years later, a Dutch scientist named Martinus W.

Beijerinck did the experiment the same as whatIwanowskis had done.

qViirology is the study of viruses.

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A. MAYER RESEARCHA. MAYER RESEARCH

Tobacco mosaic disease hindered the growth of tobacco plant (dw

Mayer conclude that The disease was caused by a very small bacterium

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DMITRI IWANOWSKI RESEARCHDMITRI IWANOWSKI RESEARCH

af extract in a way that wouldnt allow bacteria to pass through and obtained the tobac

He conclude that a bacterium was the cause

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MARTINUS W. BEIJERINCKMARTINUS W. BEIJERINCK

Beijerinck postulated the presence of an agent thatinfected the tobacco plant, although he didnt knowwhat it was.

He called the infected agent asfilterable virusbecause it couldnt pass through the bacterium filterand couldnt be observed with microscope.

The term filterable virus was shortened into Virus.

Iwanowski and Beijerinck were considered thediscoverers of Virus.

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1. SIZE1. SIZE Viruses are very small. They are between 25-300 nm

(1nm = 10-9 ).

The smallest known virus is poliovirus, it is only 25 nm

in length.Bacteriophages and Tobacco Mosai Virus (TMV) are

among the largest virusses known with 100 nm and300 nm in length,respectively.

Virus can only be observed through an electron

microscope since 1930.

A. VIRUS CHARATERISTICA. VIRUS CHARATERISTIC

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Viruses are infectious agents with both living and nonlivingcharacteristics.

1. Living characteristics of viruses

a. They reproduce at a fantastic rate, but only in

living host cells.

b. They can mutate.

2. Nonliving characteristics of viruses

a. They are acellular, that is, they contain no

cytoplasm or cellular organelles.

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b. They carry out no metabolism on their

own and must replicate using the host cell's

metabolic machinery. In other words, viruses

don't

grow and divide. Instead, new viral components

are synthesized and assembled within the

infected host cell.

c. The vast majority of viruses possess either DNA

or

RNA but not both.

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THE SIZETHE SIZE

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Viruses are usually much smaller than bacteria and are submicrosce from 5 to 300 nanometers (nm) , although some Paramyxoviruses can be up to 14,000

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Hepatitis B virus

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2. SHAPE2. SHAPEViruses have various shapes.

1. Sphere

Influenza viruses

AIDS-causing viruses (HIV) are shperes.

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AIDS-causing viruses/ HIV

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2. Rod- shaped

An example of rod- shaped virus is The Tobac

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Tobacco Mosaic Virus

bers of the family Solanaceae. The infection causes characteristic patterns (mottling an

http://en.wikipedia.org/wiki/Solanaceaehttp://en.wikipedia.org/wiki/Infectionhttp://en.wikipedia.org/wiki/Mottlinghttp://en.wikipedia.org/wiki/Mottlinghttp://en.wikipedia.org/wiki/Infectionhttp://en.wikipedia.org/wiki/Solanaceae

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Schematic model of TMV:

1. nucleic acid (RNA)2. capsomer (protomer)

3. capsid (a capsid is the protein shell of a virus.)

http://en.wikipedia.org/wiki/RNAhttp://en.wikipedia.org/wiki/Capsidhttp://en.wikipedia.org/wiki/Virus_(biology)http://en.wikipedia.org/wiki/Virus_(biology)http://en.wikipedia.org/wiki/Capsidhttp://en.wikipedia.org/wiki/RNA

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3. T- shaped

An example of T- shaped virus is the one infecting bacteria (Bacterioph

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Oval- shaped

The rabies virus is oval-shaped virus.

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3. STRUCTURE AND FUNCTION3. STRUCTURE AND FUNCTION

Virus is not a cell (Acellular).

A virus contains a particle called Virion, whichcancrystallized and shows a mineralcharacteristics rather than life.

Virus is composed of a nucleic acid and protein

coat called a capsid.

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1. Nucleic acid

vNucleic acid are moleculthat carrygenetic information.

vA virus has only one type of nucleic acidi.e. DNA (Deoxyribonucleic acid )or

RNA (Ribonuclei acid).

2. Protein envelope (capsid)vThe protein coat covering the genetic

material is called the capsid,composed of a large number proteinsubunits called capsomers.

vThe capsid giving the virus its shape.

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CAPSID / CAPSOMERSHelical Structure

Helical structure such as Tobacco

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Rod shape

Polyhedral

Polyhedral such asAdenovirus.

Capsomer

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Complex shape

Capsid

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Nucleic acid and capsid from a structure calledNucleocapsid.

In some viruses, the nucleocapsid has a membrane called

envelope.It is composed of lipids and proteins and helps the virus

to infect cells.

An example of a virus with an envelope is theInfluenzavirus.

Viruses without an envelope are called Naked Viruses.

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B. REPRODUCTION OF VIRUSB. REPRODUCTION OF VIRUS

Therere 5 steps in virus reproduction :1.Attachment

2.Penetration

3.Replication and synthesis

4.Maturation

5.Lysis