Chapter 6-Viruses and Prions Flashcards
Define: virus
-submicroscopic, infectious agents
Define: virion
-single,infectious virus particle
Define: virology
- the study of viruses
Define: bacteriophage
-viruses that infect bacteria
Define: pandemic
- worldwide outbreak of disease
Define: Hemagglutinin
- glycoproteins which cause red blood cells to agglutinate or clump together
Define: Neuraminidase
-an enzyme that catalyzes the breakdown of glycosides
Define: attenuated strain
- genetic changes that limit infectivity
Define: prophage
- in the lysogenic pathway, the result of the phage genome being incorporated into the host cells genome
Define: provirus
-formed when some viruses that cause persistent infections integrate their genome into the host cell
Define: reverse transcriptase
- virally encoded enzyme that enables retroviruses to use their single stranded RNA genome to direct formation of DNA
*basically special enzymes that carry out reverse transcription
Steps of viral replication
Attachment: naked viruses attach to host cell membranes through capsid proteins
Penetration: enveloped viruses enter through endocytosis or membrane fusion while naked viruses enter by endocytosis
Uncoating: capsid is digested by enzymes in the endocytic vesicle or cytoplasm, or nucleus
Replication: genome is replicated and viral proteins are made
Assembly: new virions are formed
Release:
*know table 6.1
*Be able to diagram and label the parts of an enveloped and non-enveloped virus
*know the function of the parts of a virus
capsid: protein shell that packages and protects the genome (also accounts for the bulk of a virions mass)
capsomere: 3D subunits that account for a capsids shape
genome: entire collection of genetic material in a cell or virus
spikes: peplomers that protrude from the viral capsid or viral envelope
envelope: lipid based; surrounds the capsid
How are viruses classified?
- ) type of nucleic acid present (DNA or RNA)
- ) capsid symmetry (helical, icosahedral, or complex)
- ) presence or absence of an envelope
- ) genome architecture (ssDNA, ssRNA, etc.)
What is antigenic drift?
- changes to the HA and NA spikes
- minor changes
- allow the virus to evade a quick antibody response by making the new strains different enough to go unrecognized by the immune system-even if the host had a prior interaction with a related strain
What is antigenic shift?
- major genetic reassortment
- broader mutations that lead to viral strains with new features, such as increased infectivity or expanded host range
What is viral genome reassortment?
-when different viral strains coinfect a host cell, their genomes mix and can generate new viral combinations
Lytic Replication (cycle)
*type of bacteriophage replication
-this pathway kills the host cell as newly made bacteriophages are released
Lysogenic Replication (cycle)
*type of bacteriophage replication
How is bacteriophage replication different from viral replication in animal cells?
- bacteriophages have a lytic or lysogenic cycle
- bacteriophages inject DNA into the host cell, while animal viruses enter via endocytosis or membrane fusion
- bacteriophages do not go through uncoating
What is an acute infection?
-viruses infect a host cell and new virions are made (nonpersistant)
What is a chronic infection?
- continuous release of virions over time and a slow progression of disease (persistent)
- HIV
What is a latent viral infection?
- flare ups with intermittent periods of dormancy (persistent)
- herpesviridae
How does HIV replicate in human cells?
How are viruses grown in the laboratory? (Bacteriophages)
Plaque assays
- bacteria are grown on a petri plate
- phage infects cell then lyse out of the cell
- infect adjacent cells
- lysed cells leave a clear zone
*each plaque represents a bacteriophage
Plaque forming units: quantity of bacteriophages in an initial volume of sample
Viral titer: quantity of virus present in a given volume of sample
How are viruses grown in the laboratory? (Animal Viruses)
- more difficult to cultivate than bacteriophages
- most are grown using tissue culture techniques
- live animal hosts may be used to support growth of some viruses
- embryonated eggs are useful for growing certain viruses
What is an oncogenic virus? What cancers does it cause?
- virus that causes cancers
- cause cancer by stimulating uncontrolled host cell division and/or decreasing host cell responsiveness to death signals
ex. ) - Human papilloma virus (HPV)
- Human T-lymphotropic virus (HTLV)
Agglutination Test
- purified antibodies linked linked to tiny latex beads
- mixed with the sample
- antibodies bind the viral antigen
- beads agglutinate
Latex Agglutination Test
- viral antigens linked to tiny latex beads
- mixed with the sample
- patient antibodies bind the viral antigen
- beads agglutinate
ELISA Test
- can be adapted to detect either antigens or antibodies in a sample (early or later infections)
- target adheres to surface
- change of color indicates binding
DNA Test
How do antiviral drugs work?
- antiviral drugs treat infections but don’t typically cure them
- vaccinations are an effective means for limiting infection
- viruses are obligate intracellular pathogens
- antivirals should be selectively toxic
- viruses have fewer chemically distinct targets than living pathogens
Antiviral Drugs
Drugs that block viral attachement, penetration and uncoating
Postexposure prophylaxis
- laboratory prepared mixture of injectible antibodies prevents viruses from binding and entering host cells
- used directly after exposure
- used to treat rabies and HIV
Docosanol
-blocks viral entry into host cells
-used to treat cold sores caused by HHV-1
Palivizumab
- injectable antibody preparation
- blocks fusion of the respiratory syncytial virus (RSV)
Antiviral Drugs-
Drugs that target viral replication, assembly, and release
Nucleoside analogs
- block replication
- activated into compounds that mimic normal nucleotides
- chemical dead end for nucleic acid replication
ex. )Acyclovir-inhibits DNA replication of HHV-1, HHV-2
Ribavirin-targets RNA polymerases syncytial virus, hepatitis C
Nucleoside reverse transcriptase inhibitors
-targer reverse transcriptase enzymes
(AZT)
Antisense antivirals
-short sequences of nucleotides complementary to the viral DNA
- bind to viral RNA inhibiting translation
- targeted RNA destroyed by cellular enzymes
- ex.) Vitravene
Interferons
- signal the presence of a virus
- neighboring, uninfected cells make defensive changes to limit viral entry and replication
seltamivir (Tamiflu) and zanamivir (Relenza)
-Prevent influenza A and influenza B virions from
budding off the host cell surface
What is a prion?
–Infectious proteins; no genetic material
–Do not replicate
–Cause transmissible spongiform encephalopathies
(TSEs)
Prion Infections
Gerstmann-Straussler-Schienker syndrome (Genetic)
•
Creuzfeldt-Jakob disease (CJD)
–
Consumption of contaminated meat
•
Chronic Wasting Disease- (Deer, Elk)
MT- S f Billings >50 deer tested positive 2017
N of Chester 3 deer tested positive
Spread thru urine, saliva, central nervous system
tissue, direct contact (feces?)
Not passed to humans?
•
Scrapie- Sheep
How are prions spread/ treatments?
Death of the host occurs from
nerve cell death leading to
sponge-like holes in brain tissue.
–
Symptoms include:
dementia.
weakened muscles.
loss of balance.
–
This results from insoluble
aggregates of abnormal prions in
the brain.
•
The human form of TSE is called
variant CJD (Creutzfeldt-Jakob
disease)
