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Lecture 2 on 1/10

What is Virion?

single virus particle

What is Capsid?

major protein component of the shell of the core; protective shell surrounding the nucleic acid genome

What is Nucleocapsid/Core?

Nucleic acid-protein assembly packaged within the virion that is a discrete substructure of the particle and surrounding protein shell. Not all virus have. HIV has one.

What is Envelope?

membrane surrounding virus core; host-cell derived lipid bilayer carrying viral glycoproteins that forms outer layer of a virus particle

What are Viruses?

smallest of all self-replicating organisms historically called filterable infectious agents

How would you describe physical features of a virus?

contains DNA or RNA as genetic material encased in a protein shell (with or without an envelope) but lacks metabolic and protein synthesis machinery

What is a Mega Virus?

an intermediate between virus and bacteria in that it has a large genome, host machinery tRNA and ribosomal elements

What is the diameter size range of Viruses?

20 nm - 450 nm

What structure do many virus tend to adopt?


Where does replication of RNA viruses occur?


Where does replication of DNA viruses occur?


What different types of Nucleocapsid Morphology are there?

helical, icosahedral, spherical, ovoid

What is host range?

the cells, tissues, species that a virus can productively infect

What is host cell range determined by?

receptor availability, presence of intracellular factors

What is susceptibility?

capacity of a cell, tissue, or species to support virus replication

What is a icosahedral?

a solid with 20 triangular faces and 12 vertices related by 2-, 3-, and 5- fold axes of symmetry

Wat are the advantages of the envelope?

protective lipid membrane full of proteins and sugars can protect against chemicals and enzymes

What are the disadvantages of envelopes?

less stable in the environment

What host cell membranes do viruses bud through to acquire their membrane?

plasma, ER, golgi aparatus, nuclear

T/F: Viral envelope proteins are post-transcriptionally targeted to the appropriate membrane


What are the general steps in virus replication?

fusion and entry into the cell, replication, assembly, release, maturation

In virus binding, what must occur?

recognition of specific protein receptors

In virus fusion/entry, what are three major mechanism?

fusion with plasma membrane, endocytosis, penetration through plasma membrane

In what case does fusion with plasma membrane occur?

enveloped virus

Explain fusion with plasma membrane.

receptor binding causes conformational change in envelope resulting in fusion with cell membrane

Explain Endocytosis

pH change causes conformational change in envelope protein and fusion with endosomal membrane and release into cytosol; virus is internalized into endosome

In what case does penetration through plasma membrane occur

non-enveloped viruses

How is uncoating initiated?

cellular signals: receptor binding, pH change

What is the virus replication complex?

must have partial to complete uncoating in order for replication to occur

What can be said about RNA viruses?

replication using viral specific polymerase; synthesis of viral proteins using host machinery

What can be said about DNA viruses?

replication of host genome may or may not use host machinery (some virus carry own polymerase); synthesis of viral proteins using host machinery

Explain the Assembly process of replication

genome incorporated as Core

Where does assembly occur?

site of membrane acquisition for enveloped viruses

What 3 types of budding/release in replication?

lytic, exocytosis, out of plasma membrane

What happens in Lytic release?

accumulation of particles until critical mass is achieved; cell death induce by viral signs and release of virions

What happens in exocytosis via cellular pathways?

recycling out of the golgi

What happens in budding out of the plasma membrane?

requires that virus has acquired plasma membrane

What happens in HIV maturation during/after budding?

viral protease protein will cleave into subunits; drug is protease inhibitor that binds protease and stunts process so virus cannot enter new target cell

T/F: Viruses are limited to particular host or cell type


T/F: Most DNA viruses replicate in the nucleus and are budded off the cytoplasm.


What are common manifestations of viral disease?

rashes, respiratory involvement, fever, swollen lymph

How does body react to viral disease?

interferon, antibodies, cytotoxic T cells

Where do most viruses enter the body through?

mucosal site in respiratory system

What are chronic infections?

virus is detectable in tissue samples, multiplying at a slow rate; symptoms mild or absent

What is an example of chronic infection?

Norwalk disease; Norovirus

What are latent infections?

after a lytic cycle, virus enters a dormant phase; generally not detectable, no symptoms; can reactivate and result in recurrent infections

What is an example of a latent infection?


What are some viruses that can cause oncolytic transformation of cells?

Epstein-Barr, Hep B (DNA) & Hep C (RNA), papillomavirus, human T-cell leukemia virus

What are some diagnostics used for viral disease?

ELISA, PCR or RT-PCR, isolation/growth in cell or animal culture

What is ELISA?

serological test for antibodies or antigens

What is PCR?

detection of viral nucleic acids in blood, mucus, excretion, tissue samples using sequence-specific viral primers; cheap and fast

What is Ribavirin?

Synthetic nucleoside analog of guanosine; activity against a broad range of both RNA and DNA viruses through multiple mechanisms of action

What are the best targets for treatment of viral disease?

unique enzymes like viral polymerases

What is Ribavirin approved for?

respiratory syncytial virus (RSV) and in combination with a-interferon for hepatitis C virus (HCV)

What DNA viruses does Ribavirin acts against?

laviviruses, paramyxoviruses, bunyaviruses, arenaviruses, retroviruses, herpesviruses, adenoviruses, and poxviruses

What mechanisms of action does Ribavirin have?

nucleoside analog; capping & elongation of RNA (RNA polymerase inhibitor); reverse transcription inhibitor

T/F: Vaccines typically do not completely block infection, but prevent disease by rapid clearance, aborting infection, or blocking transmission to target organs.


What is Active immunization?

Induces immunologic memory; can be induced by natural infection or vaccination.

What is Passive immunization?

Transfer of temporary immunity without immunologic memory.
Example: Administration of virus-specific immunoglobulins; Rabies, hepatitis B

What are prophylactic/preventative vaccinations?

ones we got as kids

What are postexposure vaccinations?

Rabies, hepatitis B, vaccinia; Can be combined with passive immunization.

What are Therapeutic vaccinations?

immunization of elderly adults reduce recurrence and symptoms

What is Adjuvant?

Immunostimulating chemicals typically derived from natural products; Makes some vaccines feel painful

When is eradication possible?

for viruses without animal reservoir, do not undergo major antigenic changes, with distinct clinical signs

What diseases are possible candidates for eradication by vaccine?

Polio, measles, smallpox

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