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Home , Adenoviridae, Animal virus, Baltimore classification, Caliciviridae, Capsid, Cytopathic effect

Chapter 6 - in Action!!

• Topics – – Classification – Multiplication – Cultivation and replication – Nonviral infectious agent – Teratogenic/Oncogenic

- Viruses have a range. That is, viruses infect specific cells or tissues of specific hosts, or specific , or specific .

Common - Viral specificity refers to the specific Cold kinds of cells a can infect. It is regulated by the specificities of attachment, penetration and replication of the virus

Properties of viruses A virion is an infectious virus - not all virus Viruses are not cells, do not have nuclei or are infectious mitochondria or or other cellular Viruses are composed of a , RNA or DNA components. - never both . Viruses replicate or multiply. Viruses do not grow. All viruses have a coat or shell that surrounds Viruses replicate or multiply only within living cells. and protects the nucleic acid core. Viruses are obligate intracellular parasites . Some viruses have a envelope or membrane surrounding a nucleocapsid core. The source of the The term virus was coined by Pasteur, and is from envelope is from the membranes of the host . the Latin word for . Some viruses package - e.g. RNA- Components of viruses - dependent-RNA or other enzymes - some do not package enzymes

1 Size comparison of viruses - how big are they? Structure

• Size and morphology • • Envelope • Complex • Nucleic acid

Mycoplasma?

There are two major of viruses called the naked nucleocapsid virus and Capsid the enveloped virus • Protective outer shell that surrounds viral nucleic acid • Capsid spikes - used for binding to cell surface • Composed of capsomer subunits - collectively protect the nucleic NAKED Enveloped acid from the environment

Nucleic acid Envelope • Viruses contain either DNA or RNA • Lipid and proteins - basically a • Possess only the to invade modified version of our and regulate the metabolic activity membranes of host cells • Envelope spikes - bind to cell • Ex. B (4 genes) and surface proteins herpesviruses (100 genes) • During release of viruses, • No viral metabolic genes , as the a part of the host membrane is virus uses the host’s metabolic taken resources

2 • – Polyhedral head – Helical tail – Fibers for attachment • Are considered either LYTIC or TEMPERATE • Are often associated with genes in bacteria - EX. - diphtheria in Clostridium diphtheriae - also Bo-Tox from C. botulinum

T-even bacteriophage penetrate the host curve for a bacteriophage by specifically binding and injecting their DNA into the host cell

After replication, bacteriophage release lysozyme , weaken/destroy/rupture cell and release numerous virions

3 Plaque

Temperate phage - formation of a Temperate phages can cause disease and LYSOGENY For example, Corynebacterium diphtheriae and Clostridium botulinum contain that have genes which encode for Without these prophages, they DO NOT produce the toxin – without toxin, no disease Thus, they are examples of bacteria and viruses interacting to cause medically relevant disease

PROPHAGE

Baltimore Classification of Animal Viruses VII ds/ss DNA Class I ds DNA (+/-) Classification Papovaviridae Class II ss DNA (+ or -) • Structure Class VI ss RNA (+) • Chemical composition Retroviridae RNA

• Genetic makeup mRNA (+) Class III ds RNA (+/-) DNA • Host relationship Class V ss RNA (-) • Type of disease Class IV ss RNA (+) Picornaviridae • of Togaviridae Flavivirida Bunyaviridae Viruses Arenaviridae Astroviridae

4 General Steps in Viral Multiplication Viruses recognize • Adsorption • Penetration specific receptors • Uncoating Figure 6.12 and then • Synthesis the virus penetrates the • Assembly cell Figure 6.13 • Release

Endocytosis Membrane Fusion

5 General Steps in Viral Multiplication • Adsorption • Penetration Replication • Uncoating • Synthesis • Assembly • Release

General replication scheme for an A Magnified View of Viral - animal virus ENVELOPED VIRUSES

Fig. i6.2a Worst case What scenario - happens if it HIV virions is a dsDNA exiting from virus??? a Examples: Herpesvirus

6 Most simple - and efficient Fig. i6.2b case = ss+RNA virus

Examples:

RETROVIRUS

Replication of RNA viruses Cytopathic effects Insight 6.2 - Note differences between + sense, - sense • Damage to the host cell due to a and replication viral –Transformation Also, be able to compare - contrast phage and animal virus replication

Viral transformation of cells –

Fig. 6.16 Cytopathic changes in cells and cell cultures infected by viruses

7 Cultivation and Replication Cultivation of animal viruses – It is possible to study viruses in , • In vivo methods but due to the complexity of the animal, expense of animals and the political – Laboratory animals environment relative to the use of animals, – Embryonic tissues alternatives have been developed. • In vitro methods Chick in - – Cell or culture Persistent infection – transformation/

A monolayer of monkey kidney cells is a cell Making the Influenza culture enabling the propagating viruses.

Noncellular Infectious – Stanley Pruisner – Nobel Agents Prize in : 1978 Prions are proteinaceous infectious • Prions agents - Prions do not have nucleic acid . Prions are considered to be the causative agents of Creutzfeld Jakob disease, , bovine spongiform encephalopathy and .

8 of the two forms of the protein GOOD!!!! BAD!!! Oncogenic potential of viruses - Cancer is a set of diseases known to disturb the normal functioning and properties of cells. Tumors may be malignant or benign - malignant tumors spread by metastasis. Peyton Rous in 1911 discovered that a filterable agent could transmit a (a type of cancer) in - - the first retrovirus described.

At least six viruses have been found to cause Viral are found usually in human cancer - Epstein-Barr virus, . virus, virus, human papilloma virus (HPV-8, HPV-16), HTLV-I (adult T-cell and ), HTLV-II (hairy cell V-oncogenes are viral homologs of the leukemia), cellular oncogenes. Oncogenes are normal cellular regulatory genes. When modified, these genes code for V-oncogenes can disturb normal products that disturb the normal regulatory patterns of cells and can result in a regulatory properties by certain loss of the normal properties of cell growth and mechanisms. division resulting in “cancer”.

Malignant tumor formation

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