Viruses Flashcards
What are the main components of viruses?
- Protein
- Nucleic acids
- Lipids
- Sugars
Virion:
The entire virus particle
Capsid:
The protein coat that surrounds the inner part of the virus
Nucleocapsid:
The protein coat that surrounds the genome
Capsomere:
Subunit of nucleocapsid
What is the basic unit of virus structure?
Capsid (coat) protein
What are the functions of capsid proteins?
- protect viral nucleic acid from environmental stresses
- interact specifically with the viral nucleic acid for packaging
- interact with host receptors for entry to cell
- allow for release of nucleic acid upon entry into new cell
- Assist in processes of viral and/or host gene regulation
Icosahedral protein coat:
Spherical
Amount of nucleic acid that can be packaged is limited by the size of the particle
“closed”
Helical protein coat:
Rod-shaped, varying widths and specific architectures
No theoretical limit to the amount of nucleic acid that can be packaged
“open”
e.g. rabies, influenza
What are DNA viruses?
- Poxviridae
- herpesviridae
- adenoviridae
- papoviridae
- hepadnaviridae
- parvoviridae
What are important RNA viruses?
- Paramyxoviridae
- orthomyxoviridae
- coranoviridae
- arenaviridae
- retroviridae
- reoviridae
- picornaviridae
- rhabdoviridae
- togaviridae
- bunyaviridae
What are functions of the viral genome?
- Genome replication
- Genome assembly and packaging
- Regulation of replication cycle
- Modulation of host defenses
What is not in the viral genome?
Genes that encode for protein synthesis machinery
Energy metabolism
Membrane biosynthesis
What are the means of virus classification?
- Presence of envelope
- Type of genome
- Disease process and/or tissue tropism
- Ability to establish latency
- Routes of transmission
Rotavirus, norovirus, and enterovirus are all known pathogens of the intestines / GI tract. Are these enveloped or non-enveloped viruses?
Non-enveloped, because lipids don’t survive gastic pH well.
Are enveloped or naked viruses more susceptible to head, acids, and drying?
Enveloped
Describe the broad differences/similarities among the Herpesvirus family?
Same/similar genome structure and general properties (all viruses with dsDNA genome, icosahedral capsid, enveloped). Alpha, beta, or gamma herpesviruses can establish latency.
Different cell tropisms and disease processes
What are the similarities/differences among the hepatitis A-D viruses?
They are primarily hepatotropic, but otherwise have many differences
HSV-1, HSV-2
- Primary infection: gingovostomatitis (mouth) or genital herpes
- Infection via direct contact
- Reactivation: cold sore or genital herpes
- Multiple other disease processes (encephalitis, hepatitis)
Varicella Zoster Virus (VSV):
- Primary infection is chickenpox (varicella)
- Reactivation is shingles (zoster)
- Varicella is much more contaigous (1-2 prior to rash onset until crusted) vs. zoster only by contact
- Varicella complications: bacterial superinfection, also pneumonitis, hepatitis, encephalitis
- Prevention: vaccine
CMV:
- Often asymptomatic, can be “infectious mono”
- Significant disease processes: congenital infections, disease in immunocompromised
EBV:
- Infectious mononucleosis
- complications varies (could cause hepatitis)
- Sequelae in the immunocompromised host
Define Sequelae:
a condition that is the consequence of a previous disease or injury.
Influenza A Virus:
- Orthomyxovirus Group
- Genome negative sense, single stranded RNA in segments
- Subtypes based on envelope hemagglutinin and neuraminidase
- Important cause of upper respiratory disease and pneumonia
Once inside cells, viruses _____, direct the production of ______ and ______, and assemble into ______
Once inside cells, viruses DISASSEMBLE, direct the production of STRUCTURAL PROTEINS and PROGENY GENOMES, and assemble into PROGENY VIRIONS
What is the generic virus life cycle?
- attachment
- entry
- uncoating
- synthesis of protein and nucleic acid
- assembly
- release
Explain the steps/regions of this one-step growth curve of virus replication
- adsorption and penetration (virion is still detectible)
- eclipse period (no intracellular virions detectible)
- maturation (progeny virion formation)
- latent period (no extracellular infectious virus detectible)
- release (budding, exocytosis, or following necrosis)
adenovirus, parainfluenza, and rhabdovirus enter host cell via ___________
Receptor mediated endocytosis
herpesvirus, HIV, and orthomyxovirus enter host cells via _____
membrane fusion
All DNA viruses except _______ replicate in the _______
All DNA viruses except Poxvirus replicate in the NUCLEUS
All RNA viruses except for _____ and _____ replicate in the ______
All RNA viruses except for RETROVIRUSES and INFLUENZA replicate in the CYTOPLASM
The site of viral genome replication is dependent on the _____
virus
Describe the process of nucleocapsid formation during the virus replication cycle:
- Accumulation of structural proteins in same cellular compartment where replication of progeny genomes occurs
- Capsid formation can happen via self-assembly or with help from scaffold proteins
For naked DNA and RNA viruses, infectious progency formation occurs as soon as genomes are encapsulated
Describe the maturation step of the virus replication cycle:
Maturation is an additonal step required only for enveloped viruses, via:
-Internal envelopment happens with ER, golgi followed by exocytosis
OR
-Cell surface envelopment
Herpesviruses, coranoviruses, bunyaviruses, and poxviruses undergo viral maturation via _______ envelopment
Internal
Rhabdoviruses, togaviruses, orthomyxoviruses, paramyxoviruses, and retroviruses undergo viral maturation via _______ envelopment
Cell-surface envelopment
The release stage of virus replication cycle has directionality, whch has implications for ______
Directionality (apical vs. basolateral) has implications for pathogenesis (localized v. disseminated infection)
Egress/release _____ often function to complete the release and maturation process
Enzymes (e.g. orthomyxo-NA, HIV-protease)
[Some enzymes are required to cleave to complete the budding, or undergo other enzymatic reactions to make sure the proteins are inactivated otherwise the virus is non-infectious]
Cytopathic Effect (CPE):
The combined effects of virus replication and inhibition of host cell macromolecular synthesis results in alteration in the appearance of the infected cells, or even cell death, termed cytopathic effect. When a uniform cell monolayer is exposed to a few infectious virus particles, visible plaques develop radially from the initially infected cells to surrounding uninfected cells.
BASICALLY some viruses give host cells characteristic shapes, and you can see from the slide immediately what type of infection the person has.
Human retroviruses:
Enveloped RNA viruses with reverse transcriptase and integrase (proviral DNA in host genome)
- Oncoviruses (Human T-cell leukemia viruses HTLV-1 and HTLV-2)
- Lentiviruses (HIV-1 and HIV-2)
- Spumaviruses (Foamy viruses, no human disease known)
- Human endogenous retroviruses (HERVs)
Lentiviruses:
Retroviruses that can infect non-dividing cells.
Includes HIV-1, HIV-2, and species-specific e.g. FIV (feline)
What is the main capsid antigen of HIV?
p24
3 major enzymes that have to be carried in by HIV (these are usually the main targets for antiviral agents):
- reverse transcriptase
- integrase
- HIV protease (activates the virus as it leaves)
Describe the process of HIV entry into the host cell:
- Mediated via interactions of env. gp120/gp41 with cellular receptors
- CD4 is the primary receptor
- CCR5 or CXCR4 are co- or secondary receptors)
- Sequences within gp120 (mostly the V3 loop) determines co-receptor usage
What cells contain CD4?
Most T lymphocytes
BUT ALSO
macrophages
microglial cells (dendritic cells)
What are the first three steps of viral replication cycle?
- Step one HAS TO BE GP120 of HIV interacts with CD4
- Causes a conformational change of GP120 which allows it to react with the chemokine receptor
- There interactions cause a conformational change in GP41 which starts to attack the cell
_____ is used by most virus strains as a coreceptor (prevalent early). Some viruses evolve to use _____ later in infection.
CCR5 is used by most virus strains as a coreceptor (prevalent early). Some viruses evolve to use CXCR4 later in infection.
Describe the process of reverse transcription:
- The ssRNA strand serves as a template for the reverse transcriptase enzyme, which generates a DNA strand (have 1 RNA, 1 DNA now)
- RNAse H degrades the RNA
- A second strand of DNA (complimentary to the first DNA strand) is produced with DNA dependent DNA polymerase, resulting in dsDNA
[these 3 enzymes are carried with the virus]
What is the purpose of HIV integrase enzyme?
Integrates the HIV DNA into the human chromosome, helps identify the integration site on host DNA.
Executes strand transfer.
What is the purpose of the protease enzyme of HIV?
Activates the virus as it buds off from the host cell
