16 - Infeksi Virus

8/10/2019 16 - Infeksi Virus

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MUHAMMAD ASAAD MAIDIN

Department of Microbiology, Faculty of Medicine,Hasanuddin University, Makassar


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The objectives are that students should beable to know and understand

1. The nature, structure and classification

of viruses.2. The differences of replication cycle of

viruses between DNA and RNA.

3. The ability of viruses to cause disease

and effect viruses on host.


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PROPERTIES OF VIRUSES

1. Virus structure consist of : Nucleic acid ,

capsomer / capsid and envelope

2. Genome can be either DNA or RNA3. Viruses do not have ribosome

4. Viruses do not replicate by binary fission

5. Viruses range from 18 nm to 300 nmin diameter.


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6. Obligate intracellular organisms

7. Sensitive to interferon

8. No sensitivity to antibiotics

9. Can not grow on artificial media.


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STABILITY OF VIRUSES

- Stable when added MgCl2, MgSO4,Na2SO4

- Stable is important for preparing vaccine.

PH 5.00 -9,00

- When exposed to ultra violet lamp loss

activity.


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CHEMISTRY PROPERTIES OF VIRUSES

Destroyed on 50o-60oC,with in 30.

Can be kept in -70oC for several months

and in -170oC for years in Nitrogen tank.

To keep in -170C must be mixed with

dimethyl sulfoxide (DMSO) 5 % for

maintenance their activity.


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Gbr 3.

DNA double helix

Sugar-phosphate

backbone

Nucleotides


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DNA double helix

Three dimension


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NAKED ICOSAHEDRAL

NAKED HELICAL


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3. Enveloped icosahedral symmetry, e.g. herpesvirus, yellow fever virus, rubella virus

4. Enveloped helical symmetry, e.g. rabies virus,

influenza virus, para influenza virus, mumps

virus, measles virus

5. Complex symmetry e.g. poxvirus


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COMPLEX SYMMETRY; POX VIRUS


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Basic Classification of Viruses

Nucleic acid

- RNA or DNA

- single-stranded or double-stranded

- nonsegmented or segmented

- linear or circular

- if genome is single stranded RNA, canit function as mRNA?

- whether genome is diploid (it is in

retroviruses)

Virion structure

- symmetry (icosahedral, helical,complex)

- enveloped or not

- number of capsomers


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GLOSSARY :

1. Capsid : The protein coat that surrounds the

nucleic acid of a virus.

2. Nucleo Capsid : The virus structure composed

of the nucleic acid surrounded by the capsid.

3. Capsomer : Substructure of virus particle.

4. Genome : A set of genes


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5. Envelope : A host cell derived membrane,

containing virus specific antigens, thats is

acquired during virus maturation.

6. Virion : the mature virus particle, with all

of its structural components intact.


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T-Lymphocyte

Muh.Asaad Maidin

Glucoprotein virus

Attached to receptor CD4& co-receptor of sel T


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Muh.Asaad Maidin

Penetration anduncoating

T-Lymphocyte


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DNA Virus Replication


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DNA Virus Replication


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DNA VIRUS REPLICATION

e.g. Adeno virus

1. Attachment, Penetration and uncoating

Viral capsid proteins interact with cell

surface receptors and penetration is probably via

endocytosis.Virion are transported to the nucleus

and uncoated. DNA enter nucleus, probably

through a nuclear pore.


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2.Early transcription and early translation :

Adenovirus uses host cell polymerase, early

mRNA trascribed and mRNA processed by host

cell. The DNA replicateby a strand displacementmechanism.

3. Late transcription and late translation :

Late mRNA code predominantly forstructural proteins.


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4. Assembly :occurs in the nucleus DNA

enters the particles after immature capsidare formed.The capsid undergo amaturation process, after which the celllyse and the virion leak out.

5. Budding/ release. Virions may bereleased due to cell lysis.Budding virusesdo not necessarily kill the cell, some may

be able to set up persistence.


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RNA VIRUS REPLICATION

1). RNA virus do no t copy thei r RNA into

DNA.

2). RNA virus which copy thei r RNA into

DNA


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1). RNA virus do no t copy their RNA into DNA.

Need an RNA-dependent RNA-po lymerase to

repl icate their RNA.

No vira l protein can be made unt i l vi ra l m -RNA

available.


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1.1. Plus st randed RNA v iruses.

The virion RNA is the same sense as

m-RNAsofunct ion as m-RNA.Thism-RNA can be translated immediately

upon infection of the host cell.

eg. Picornavirus , polio virus, togavirus,flavivirus


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1.3. Doub le stranded RNA viru s (dsRNA)

The virion RNA is doub le stranded so

cannot function as m-RNA needed

RNA- po lymeraseto make mRNA

e.g. Rotavirus


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2). RNA viruses which copy their RNA into DNA .

Retroviruses although plus-sense, virion

RNA is not release in the cytoplasm,so

does not function as mRNA. Vir ion RNA serve

as a template for Reverse transcr iptaseenzyme (RT)imm ediately cop ied into DNA .Retroviruses need to code RT enzyme and

package it in virion.


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There are four main effects of virusinfection on the cell:

1. Death

2. Fusion of cells to form multinucleated cells.3. Malignant transformation

4. No apparent morphologic or function

change


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References ;

1. Cohen,J., Powderly,W.G.,et al, 2004.

Infectious Diseases, 3 rd edith. Mosby.2. Levinson, W., and Jawetz, E., 2002 Medical

Microbiology, a Lange medical book, seventh edith.

3. Metseelar, D., and Simpson,D.I.H.,1982.

Practical virology, For Medical Students andPractisioners in Tropical Countries, Oxford Univ.Press.

4. Mims,C.,Dockrell,H.M, et al, 2004.

Medical Microbiology, 3rdedith.Elsevier Mosby.

5. Virella, G., 1997. Microbiology and Infetious Diseases,

3rdedition,William & Wilkins a waverly company.

6. Internet.


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16 - Infeksi Virus