Microbiology Chapter 13; General Characteristics of viruses
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)