Viruses Flashcards
Obligate intracellular parasites lacking the capacity to make energy or substrates
Viruses
How do viruses replicate?
By assembly of parts
NOT binary fission
The basic structure of a virus is nucleic acid surrounded by a _____ coat
Protein coat
Is viral nucleic acid circular or linear?
Can be either
Outer protein coat of viruses made of capsomeres (subunits forming pentons and hexons)
Capsid
The viral capsid is an outer protein coat made of these
Capsomeres (subunits forming pentons and hexons)
What gives viruses their shape?
Capsid
Viral architecture that is resistant to drying, acid, detergents, and bile
Capsid
Protein coat with the nucleic acid inside
Nucleocapsid
Lipid membrane acquired from a host cell membrane through budding
Susceptible to organic solvents
Envelope
The viral envelope is susceptible to this
Organic solvents
The viral envelope is this
Lipid membrane acquired from host cell membrane through budding
The space between the capsid and the envelope
Tegument
The tegument is the space between these
Capsid and envelope
Are host proteins found in isolated enveloped viruses?
No
These can associate with the glycoproteins in the viral envelope to localize capsid formation to the appropriate location
Viral matrix proteins
What localizes viral capsid formation to the appropriate location?
Viral matrix proteins that associate with glycoproteins in the envelopes
Complete infectious virus particle
Virion
For naked viruses, this is the virion
Nucleocapsid
For enveloped viruses, this is the virion
Nucleocapsid with the envelope
6 stages of the lytic replication cycle for animal viruses
- Attachment
- Penetration and uncoating
- Targeting to the site of reproduction
- Synthesis (txn and tln)
- Assembly
- Release
2 enzymes required for some viruses that are not found in human cells
RNA-dependent DNA pol (make DNA from RNA)
RNA-dependent RNA pol (make RNA from RNA)
Do DNA viruses require extra enzymes not found in the host?
No; just use host enzymes
In the early phase of viral genome replication, these products are made first
Early gene products: non-structural proteins
Viral polymerases and regulatory molecules needed for further replication
In the late phase of viral genome replication, these products are made
Structural proteins, mainly capsid proteins
Genome replication triggers this step
What type of host cells are required for viral genomic replication and expression?
Rapidly growing host cells
Do small or large viruses typically use host polymerases?
Small
Do small or large viruses typically encode their own polymerases?
Large
Type of virus that can be directly translated by host cell machinery to make virus proteins
+ssRNA
All RNA viruses except retroviruses require this enzyme for genome replication
RNA-dependent RNA pol
3 types of viruses that require their own RNA-dependent RNA pol
+ssRNA, -ssRNA, and dsRNA
Type of virus that must encode an RNA-dependent RNA pol that is packaged in the capsid
-ssRNA
Difference in polymerase requirements between +ssRNA and -ssRNA viruses
Both require their own RNA-dep RNA pol, however -ssRNA must have it packaged in the capsid
Type of RNA virus that can be directly translated
+ssRNA
A retrovirus virion contains these 3 things
2 identical +ssRNA molecules
2 tRNA molecules
Reverse transcriptase (RNA-dep DNA pol)
How does reverse transcriptase replicate retroviral genome?
Produces cDNA copy of the RNA genome in the cytoplasm
cDNA enters the nucleus and integrates into the host genome
Host txn makes viral mRNAs from the integrated cDNA template
Reverse transcriptase produces cDNA from the viral RNA genome in this intracellular location
Cytoplasm
cDNA then enters the nucleus and integrates into the host genome
When does viral assembly begin?
Begins when viral “pieces” reach a high enough concentration to induce self assembly
Scaffolding proteins may be involved in this step of viral replication
Assembly
DNA viruses assemble in this intracellular location
Nucleus
RNA viruses assemble in this intracellular location
Cytoplasm
Type of viruses that assemble in the nucleus
DNA
Type of viruses that assemble in the cytoplasm
RNA
Step of viral replication where enveloped viruses acquire the lipid membrane in a process known as budding
Release
Enveloped viruses acquire the lipid membrane during release in a process known as this
Budding
Budding (process where enveloped viruses acquire the lipid membrane) can occur in these 4 cellular locations
Plasma membrane
Nuclear membrane
ER
Golgi
Viruses cause pathologic effects, called cytopathic effect, by these 4 mechanisms
Lysis
Vacuolization
Inclusion bodies
Cell fusion (syncytia)
Viral infections that fail to produce any symptoms in the host are called:
Inapparent or subclinical
2 components of viruses that can be identified in cytologic examination
Syncytia and inclusion bodies
Laboratory diagnosis method:
May not be a standard clinical laboratory technique but can be used to detect and identify a virus
Electron microscopy
Laboratory diagnosis method:
Is usually unnecessary and avoided to reduce the risk to laboratory personnel
Virus isolation
In serology, a ______ -fold increase in antibody titer is needed between acute phase and convalescent sera
4 fold increase
Detection of this Ab is likely an active acute infection
IgM
Proteinaceous infectious agent, linked to a number of fatal human diseases
Prion
Prions cause this
Brain degeneration
Brain tissue develops sponge-like holes termed transmissible spongiform encephalopathies
Symptoms may not appear for years after infection (slow infection)
Transmissible spongiform encephalopathies are indicative of this
Prions
Do symptoms from prion infection appear rapidly or slowly?
Slow infection; symptoms may not appear for years after infection
Normal cellular PrP protein has this secondary structure
Alpha helices
PrP with alpha helices is this
Normal cellular PrP protein (made by all mammals)
PrP with beta pleated sheets is this
Disease causing form called prion PrP
Prion PrP (disease causing form) has this secondary structure
Beta pleated sheets
Prion PrP (disease causing form) is resistant to these 3 things
Proteases, nucleases, and UV light
Characteristic of prions that makes it a slow infection
Prion PrP changes shape of cellular PrP so it becomes prion PrP
