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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