Microbiology Chapter 13; General Characteristics of viruses

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Plaques

Formed from bacteriophges, clearing on a lawn of bacteria

HIV-2

Related to viruses that infect monkeys

Temperate phages

latent(non-productive cycle)

Lytic replication

replication cycle usuallyresults in death and lysis of host cell -produces more virions:productive cyle

Virion

Complete, fully developed viral particle

Generalist

Infect many kinds of cells in many different hosts

Lysogenic replication

infected host cells grow and reproduce normally for generations before they lyse

HIV-1

related to viruses that infect chimpanzee and gorillas

Virion

two identical RNA strands packaged into conical capsid

Characteristics of viruses

-contain DNA or RNA -contain a protein coat -no ribosomes, cytoplamic membran, cytosol, organelles

Lysogeny

Phage remains latent phage DNA incorporates into host cell dna

Spikes

projections from outer surface; glycoproteins used for attachment

Specialized transduction

Specific bacterial genes transferred to another bacterium via phage -changes genetic properties of bacteria

Cytopathic effects

visible effects of viral infection on a cell -loss of contact inhibition leading to cancer -producing interferons to protect uninfected cells

Prions

inherited and transmissible by ingestion, transplant, and surgical instruments -brain degeneration -transmissible spongiform encephalopathies -symptoms don't appear for years

Lytic cycle

phage causes lysis and death of host cell -Generalized transduction

Viruses and cancer

-genetic material of oncogenic viruses often becomes integrated into host cells dna and induce tumors

Lysogenic cycle

-prophage DNA incorporatd in host DNA

Multiplication of animal viruses

Attachment:Viruses attach to cell membrane using spikes Penetration:endocytosis or fusion Biosynthesis: RNA virus replication and protein synthesis Maturation: nucleic acid and capsid proteins assemble Release:budding, rupture/lysis, exocytosis, or host cell apoptosis

The Lytic cycle

Attachment:phage attaches by tail fibers to host cell Penetration:phage lysozyme opens cell wall;tail sheath contracts to force tail core and dna into cell Biosynthesis:prodoction of phage dna and proteins Maturation: Assembly of phage particles Release:phage lysozyme breaks cell wall

Complex viruses

Complicate structures, bacteriophage

Polyhedral viruses

Many-sided

PrPsc

Mutated scarpie protein; foldsdifferently and accumulated in brain cells forming plaques -resistant to proteases -resist UV light and nucleases

Bacteriophages

Viruses that infect bacteria

Nonlatent hiv

can survive more than 1.5 days inside a cell

Helical viruses

hollow, cylindrical capsid

Envelope

lipid, protein, and carbohydrate coating

PrPc

normal cellular prion protein , on the cell surface

Activate oncogenes

transform normal cells into cancerous-derived from animal cells

Host range

the spectrum of host cells a virus can infect

Transformed cells exhibit

-increased growth -loss of contact inhibition -immortalization -lose anchorage dependency -have fewer growth factor requirements

Intracellular state

-metabolically active -capside removed -virus exists as nucleic acid

Obligatory intracellular parasites

-no atp generation -require living host cells to multiply -no response to environment

Impact of HIV infection

-older adults and young children do not have fully developed immune system = more susceptible

embryonated eggs

-virus injected into the egg -viral growth signaled by changes or death of the embryo

Retroviridae

Viral RNA is transcribed to DNA using reverse transcriptase which can integrate into host DNA

Lysogenic conversion

When phages carry genes that alter phenotype

HIV transmission

intimate sexual contact, breast milk, transplacental infection, contaminated needles, organ transplant, blood transfusion

Tissue/cell culture

tissues are treated with enzymes to seperate cells viral infected cells are detected via their deterioration(cytopathic effect)


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