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
DNA Viruses/Double-Stranded DNA
enveloped
Enveloped Poxviridae Orthopoxvirus (vaccinia and smallpox viruses) Molluscipoxvirus Smallpox Molluscum contagiosum Cowpox Herpesviridae Simplexvirus (HHV-1 and HHV-2) Varicellovirus (HHV-3) Lymphocryptovirus (HHV-4) Cytomegalovirus (HHV-5) Roseolovirus (HHV-6 and HHV-7) Kaposi’s sarcoma (HHV-8) Some herpesviruses can remain latent in host cells Hepadnaviridae Hepatitis B virus Use reverse transcriptase
RNA Viruses/Single-Stranded
noneenveloped
\+ strand Picornaviruses Enterovirus Poliovirus and coxsackievirus Rhinovirus Hepatitis A virus Caliciviridae Hepatitis E virus Norovirus causes gastroenteritis
RNA Viruses/Single-Stranded
enveloped
+ strand
Togaviridae Alphavirus Transmitted by arthropods; includes EEE and WEE Rubivirus (rubella virus) Flaviviridae Arboviruses can replicate in arthropods; include yellow fever, dengue, SLE, and West Nile viruses Hepatitis C virus Coronaviridae Upper respiratory infections Coronavirus SARS
RNA Viruses/Single-Stranded
enveloped
- strand
Rhabdoviridae Vesiculovirus Lyssavirus (rabies virus) Cause numerous animal diseases Filoviridae Filovirus Ebola and Marburg viruses Paramyxoviridae Paramyxovirus Morbillivirus Parainfluenza Mumps Newcastle disease (chickens) Deltaviridae Hepatitis D virus Depends on coinfection with hepadnavirus
RNA Viruses/Single-Stranded
enveloped
- strand
Multiple strands Orthomyxoviridae Influenzavirus (influenza viruses A and B) Influenza C virus Bunyaviridae Bunyavirus (CE virus) Hantavirus Arenaviridae Helical capsids contain RNA-containing granules Lymphocytic choriomeningitis VEE and Lassa fever
RNA Viruses/Double-Stranded
Nonenveloped Reoviridae Reovirus (respiratory enteric orphan) Rotavirus (mild respiratory infections and gastroenteritis) Colorado tick fever
Retroviridae
Single-stranded RNA, two RNA strands, produce DNA
Use reverse transcriptase to produce DNA from viral genome
Lentivirus (HIV)
Oncogenic viruses
Includes all RNA tumor viruses
Prions
Proteinaceous infectious particle
Inherited and transmissible by ingestion, transplant, and surgical instruments
Spongiform encephalopathies: sheep scrapie, Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker syndrome, fatal familial insomnia, mad cow disease
PrPC: normal cellular prion protein, on cell surface
PrPSc: scrapie protein; accumulates in brain cells, forming plaques
Plant Viruses and Viroids
Plant viruses Enter through wounds or via insects Viroids Infectious RNA No protein coat Example: potato spindle tuber disease
