Microbiology Chapter 13 Flashcards
general characteristics of viruses
Obligate intracellular parasites No ATP-generating mechanism No ribosomes Contain DNA or RNA at one time Contain a protein coat Some viruses 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
virion, an entire virus particle, consisting of an outer protein shell called a capsid and an inner core of nucleic acid (either ribonucleic or deoxyribonucleic acid—RNA or DNA)
All viruses Nucleic acid DNA or RNA at one time Protein Coat = Capsid Building blocks known as capsomeres Some viruses Envelope Spikes
Virion Morphology
Polyhedral(mastedenovirus animal virus)
Helical(ebola virus nonevelope) (influenza envelpoed virus)
Complex(bacteriophage, T-even virus)
viral structures
polyhedral: nucleic acid,capsomere, capsid
helical: nucleic acid, capsomere, capsid, (enveloped) spikes
complex: capsid head, sheath stem, dna, tail fiber, pin baseplate
Family names end in -viridae Genus names end in -virus Viral species: a group of viruses sharing the same genetic information and ecological niche (host) Common names are used for species Subspecies are designated by a number
Virus Taxonomy
Viruses must be grown in living cells
Bacteriophages form plaques on a lawn of bacteria Animal viruses Living animals Embryonated eggs Cell culture Continuous cell lines
Cytopathic effects Serological tests Detect antibodies against viruses in a patient Use antibodies to identify viruses in patient Neutralization tests Viral hemagglutination Western blot Nucleic acids RFLPs PCR
viral identification
Results of Multiplication of Bacteriophages
Lytic cycle Phage causes lysis and death of host cell Lysogenic cycle Prophage DNA incorporated in host DNA Phage conversion Specialized transduction
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: production of phage DNA and proteins
Maturation: assembly of phage particles
Release: phage lysozyme breaks cell wall
Multiplication of Animal Viruses
Attachment: viruses attach to cell membrane
Penetration by endocytosis or fusion
Uncoating by viral or host enzymes
Biosynthesis: production of nucleic acid and proteins
Maturation: nucleic acid and capsid proteins assemble
Release by budding (enveloped viruses) or rupture
Know meachnism of various kinds of viruses
DNA coating animal virus, RNA containing virus, Retrovirus
Cancer
Activated oncogenes transform normal cells into cancerous cells
Transformed cells have increased growth, loss of contact inhibition, tumor-specific transplant antigens, and T antigens
The genetic material of oncogenic viruses becomes integrated into the host cell’s DNA
Latent and Persistent Viral Infections
Virus remains in asymptomatic host cell for long periods
Cold sores, shingles
Disease process occurs over a long period; generally is fatal
Subacute sclerosing panencephalitis (measles virus)
DNA Viruses/Single-Stranded DNA
Nonenveloped
Parvoviridae
Fifth disease
Anemia in immunocompromised patients
DNA Viruses/Double-Stranded DNA
noneveloped
Adenoviridae Respiratory infections in humans Tumors in animals Papovaviridae Papillomavirus Human wart virus Polyomavirus Cause tumors; some cause cancer
