CH 13: Viruses, Viroids, and Prions

Viruses

•Viruses contain DNA or RNA

•And a protein coat

•Some are enclosed by an envelope

•Some viruses have spikes

•Most viruses infect only specific types of cells in one host

•Host range is determined by specific host attachment sites and cellular factors

•Multiply inside living cells using the machinery of the host

Virion

is a fully developed, infectious viral particle composed of nucleic acid surrounded by a protein coat

Viruses

are classified by differences in the structures of these coats

bacteriophages/ phages

•Viruses that infect bacteria

Shapes - Helical Viruses

shapes - Polyhedral Viruses

Shapes - Complex Viruses

Viral Taxonomy

(Family, Genus, Species, Subspecies)

1.Herpesviridae

2.Herpesvirus

3.Human herpes virus 1, HHV 2, HHV 3

1.Retroviridae

2.Lentivirus

3.Human Immunodeficiency Virus 1, HIV 2 (AIDS)

Growing Viruses

•Viruses must be grown in living cells.

•Bacteriophages form plaques or clearing areas

Growing Viruses

•In the laboratory, three methods are commonly used for culturing animal viruses: using living animals, embryonated eggs or cell cultures & use cell lines

•Animal viruses may be grown in living animals or in embryonated eggs

Virus Identification – cytopathic effect

Multiplication cycle of phages occurs in five distinct stages

1. Attachment

2. Penetration 

3. Biosynthesis

4. Maturation

5. Release

Attachment

Phage attaches by tail fibers to host cell

• Viruses attaches to cell membrane

Penetration

Phage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell

• By endocytosis or fusion

uncoating

• By viral or host enzymes

Biosynthesis

Production of phage DNA and proteins

• Production of nucleic acid and proteins

Maturation

Assembly of phage particles

• Nucleic acid & capsid proteins assemble

Release

Phage lysozyme breaks cell wall

• By budding (enveloped viruses) or rupture

Lytic cycle

Phage causes lysis and death of host cell

Lysogenic cycle 

Prophage DNA incorporated in host DNA

Attachment, Penetration, and Uncoating

Release of an enveloped virus by budding

Multiplication of a Retrovirus* (like HIV)

Cancer

•Almost anything that can alter the genetic material of a eukaryotic cell has the potential to make  normal cell cancerous

•These cancer-causing alterations to cellular DNA affect arts of the genome called oncogenes

•Activated oncogenes transform normal cells into cancerous cells

•Mutagenic chemicals, radiation and some viruses can activate oncogenes and lead to cancer

•Transformed cells have increased growth, loss of contact inhibition

•The genetic material of oncogenic viruses becomes integrated into the host cell's DNA

Very general knowledge question like how its carcinogenic and the chemicals being bad for you etc.

Just read it

Latent Viral Infections:

•Virus remains in asymptomatic host cell for long periods

• Cold sores

Persistent Viral Infections:

•Disease processes occurs over a long period, generally fatal

• Subacute sclerosing panencephalitis (measles virus)

Prions

•Infectious proteins

•Inherited and transmissible by ingestion, transplant, & surgical instruments

•Spongiform encephalopathies: Sheep scrapie, Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker syndrome, fatal familial insomnia, mad cow disease

Plant Viruses

enter through wounds or via insects

Viroids

are infectious RNA; potato spindle tuber disease