TEST 2 Intro to Virology Flashcards
Define Capsid:
The protein shell, or coat, that encloses the
nucleic acid genome.
Define Nucleocapsid:
The protein–nucleic acid complex
representing the packaged form of the viral genome.
Define Capsomeres:
Morphologic units seen in the electron microscope on the surface of icosahedral virus
particles.
Define Envelope:
A lipid-containing membrane composed of lipids, proteins, and glycoproteins that surrounds some virus particles.
Define Virion:
The Complete virus particle
Define Icosahedral:
In which the capsomeres are arranged in 20 triangles that form a symmetric figure (an
icosahedron) with the approximate outline of a sphere.
Define Helical:
In which the capsomeres are arranged in a hollow coil that appears rod-shaped. The helix
can be either rigid or flexible.
A Naked Capsid has what properties?
- It is environmentally stable to the following:
- Temperature
- Acid
- Proteases
- Detergents
- Drying
- Is released from cell by lysis
A Envelope has what properties?
- It is environmentally labile—disrupted by the following:
- Acid
- Detergents
- Drying
- Heat
- Modifies cell membrane during replication Is released by budding and cell lysis
What are the components of a naked capsid?
Protein
What are the components of a envelope?
- Membrane, Lipids, Proteins, and Gylcoproteins.
What are two examples of internal viral proteins?
- Structural: Capsid proteins of the enveloped viruses.
- Enzymes: Polymerases that synthesizes the viral mRNA.
What is the tegument?
- Structure found in herpesvirus family
- Contains regulatory proteins including transcription and translation factors that control either viral or cellular processes.
Define envelope-associated proteins?
- Membrane lipoproteins
- (lipids derived from the host membrane; proteins are virus-specific)
- Glycoproteins
- (spikes, attach to host cell receptors, viral attachment proteins (VAP)
- Matrix Proteins
- (mediate the interaction between the capsid proteins and the envelope)
What are antigenic variants?
Surface proteins that allow the viruses to evade our host defenses. These variants give it a unique serotype that antibodies must be built to fight.
Describe the Early phase of infection?
- Virus recognizes target cell
- Attachment
- Penetration of plasma membrane and taken into the cell.
- Release (uncoat) its genome into the cytoplasm.
- If necessary, deliver genome to the nucleus.
Describe the Late phase of infection?
- Starts with genome replication and viral macromolecular synthesis.
- Viral Assembly
- Release
Describe the eclipse period?
- Period in which uncoating of the genome from the capsid or envelope abolishes its infectivity and identifiable structure.
Describe the latent period?
- Extracellular infectious virus is not detected
- Includes eclipse period and ends with the release of new viruses.
Describe defective particles?
- Noninfectious particles, resulting from mutations and errors in the manufacture and assembly of the virion.
- 90-99% of particles released are defective.
Describe Burst size?
- Yield of infectious virus per cell.
Describe productive infections?
Occurs in permissive cells and results in the production of infectious virus.
Describe Abortive infections?
- Fail to produce progeny
- Occurs due to the cell being nonpermissive (unable to support the expression of all viral genes or because the infecting virus may be) or due to the viral particles being defective.
Describe Latent infection?
Occurs with the persistence of viral genomes, the expression of no or a few viral genes, and the survival of the infected cell.
What are VAPs and how do they function?
- Virion attachment proteins, or spikes, are protein molecules on the surface of the virion that bind to receptors so that adsorption occurs.
Describe Host Range?
Virus is capable of only infecting a limited range of cells. Most viruses can infect only one species.
Describe tissue tropism?
The virus only infects a certain subset of cells in the host organism.
What is the cause of host range, and tissue tropism?
Due to the presence or absence of receptors.
Describe the Early gene products?
- DNA-Binding proteins and enzymes, including virus-encoded polymerases.
- These proteins are catalytic, and only a few are required.
Describe Late viral genes?
- Encode structural and other proteins
- Many copies of these proteins are required to package the virus but are generally not required before the genome is replicated.
What is the crucial step in the takeover of the cell by the virus?
The production of the first viral mRNAs at the beginning of the infection.
What directs synthesis of viral proteins?
Virus-specific mRNAs
Most DNA viruses synthesize their mRNAs by using what?
Host RNA polymerase.
How are RNA genomes of retroviruses copied into the DNA strands? and Which DNA strand?
- Reverse transcriptase (RNA dependent DNA polymerase)
- Subsequently converted to ds-DNA.
- (-) DNA
Host RNA polymerase transcribes what into what?
- viral DNA
- viral mRNA and genomic RNA
Describe the process of encapsidation?
The process of enclosing the viral genome in a protein capsid.
Describe the process of encapsidation?
The process of enclosing the viral genome in a protein capsid.
The four general principles that
- The process generally involves self-assembly of the component parts.
- Assembly is stepwise and ordered.
- Individual protein structural subunits or protomers are usually preformed into capsomeres in prep for the final assembly process.
- Assembly often initiates at a particular locus on the genome, the packaging site.
What are the two main strategies of viral release?
- Cell Death
- Common in naked capsid viruses
- Budding
- Common in enveloped viruses.
- This is how they gain their envelope.
The process by which viruses cause disease in the host is termed?
Viral Pathogenesis
Complex interactions between the virus and susceptible host result in?
Disease
The time between exposure to the organism and appearance of the first symptoms of the disease.
Incubation period.
What is the incubation period said to be if it proceeds without symptoms?
Asymptomatic
What is the term for when the incubation period produces nonspecific early symptoms, such as fever, head/body aches, or chills?
Prodrome
The ability of the organism to shed in secretions, which may occur early in the incubation period.
Communicability
Example of a virus that can integrate into the host genome?
HIV
Example of a virus that survive by slow replication in the presence of an immune response?
Hepatitis B and C
Describe a localized infection?
The virus spreads mainly by infecting adjacent or neighboring cells
Describe systemic disease?
- The virus spreads from the site of entry to the target tissue, where they cause cell injury after multiplication.
- Occurs via bloodstream and neural paths.
Describe Viremia?
Develops when the virus is detected in blood.
Describe viral replication in a semipermissive cell.
May be very inefficient, or the cell may support some but not all the steps in viral replication.
Define Virulence?
Relative ability of a virus to cause disease.
Define Cytopathogenicity?
The ability of a virus to cause degenerative changes in cells or cell death.
Define virulent viruses?
Viral strains that kill target cells and cause disease.
Describe avirulent or attenuated strains?
Strains that have mutated and lost their ability to cause cytopathic effects (CPE) and disease.
Describe unapparent infections?
Subclinical, and the individual is referred to as a carrier.
What are the three major outcomes of viral infection?
- Abortive infection
- Lytic infection
- Persistent infection
Describe Abortive Infection
No progeny virus particles are produced, but the cell may die because early viral functions can occur.
Describe Lytic Infection?
Active virus production is followed by cell death.
Describe persistent infection?
Small numbers of virus particles are produced with little or no CPE.
What are the three types of persistent infections??
- Latent infection
- Chronic infection
- Viral Transformation
Describe Latent infection?
Viral genetic material remains in host cell without production of virus and may be activated at a later time to produce virus and/or transform the host cell.
Describe chronic infection?
Involves low level of virus production with little or no CPE.
Describe Viral Transformation?
Viral infection or viral gene product induces unregulated cellular growth, and cells form tumors in the host.
Describe viral interference?
When two closely related viruses infect a host, infection by the first virus can inhibit the function of the second virus.
The relative susceptibility of a person and the severity of the disease depend on the following factors:
- The mechanism of exposure and site of infection.
- Immune status, age, and general health of the person.
- Viral dose
- Genetics of the virus and the host.
The two major host defenses are?
Nonspecific (innate)
Specific (adaptive)
Describe interferons?
- Part of innate immune response.
- Cytokines, produced by virally infected cells that inhibit virus production in infected and other cells.
- Activate pathways that:
- degrade mRNA
- inhibit protein synthesis.
- Activate pathways that:
Describe two of the components of the adaptive immune response.
- Directed by antigens
- Antibodies are effective in eliminating cell-free virus
- Cytotoxic T lymphocytes (CTL) destroy virus-infected cells.
Describe the Viral cytopathologic effects discussed in class.
- Cell Death
- Characteristic histologic changes
- Syncytia
- Cell surface changes
Describe Hemadsorption?
- Attachment of erythrocytes to the surface of virus-infected cells.
- Limited to viruses that have:
- Hemaglutinin protein on their envelope.
- Mumps, parainfluenza, and influenza.
Describe Interference?
- Formation of a CPE by a second virus.
- Examples:
- Rubella virus which does not cause a CPE.
- Can be detected by interference with the formation of a CPE by certain enteroviruses.
- Rubella virus which does not cause a CPE.
Describe the detection of a decrease in acid production by infected, dying cells.
The indicator remains red (alkaline) in the presence of virus-infected cells but turns yellow in the presence of metabolizing normal cells.
Can detect enteroviruses.
Describe seroconversion?
Term used to describe the finding of antibody to a virus in a patient’s serum when the patient previously had no antibody.
Neutralization and Hemagglutination Inhibition tests assay what?
Antibody based on its recognition of and binding to virus.
What are the Limitations of Serologic Methods?
- Presence of antiviral antibody indicates previous infection but not when it occurred.
- False-positive or false-negative test results may confuse the diagnosis.
- Serologic cross-reactions between different viruses may also confuse the identity of the infecting agent.
- Antibody used in the assay may be too specific and may not recognize strains of virus. (False-negative)
How are protein patterns detected?
Electrophoresis
How are enzyme activities detected?
Reverse transcriptase
