Viral Structure Flashcards
How are viruses similar to living organisms?
proteins
glycoproteins
nucleic acids
How are viruses dissimilar to living organisms?
no polysaccharides
lipids are only found in enveloped viruses
viruses don’t have ribosomes (arenavirus exception)
Describe characteristic of DNA viruses.
Single or double stranded
linear or circular
open or closed ends
continuous or nicked
Describe characteristics of RNA viruses.
single (+ / - sense) or double stranded
linear
may be segmented
What is positive sense?
5’ to 3’
What is negative sense?
3’ to 5’
List the component of the basic virion.
Nucleic acid
Capsid - protein coat that encloses nucleic acid
-made of capsomers
Tegument - proteinaceous material between envelope and capsid
Envelope - not in all viruses
Name the two basic capsid symmetries of the viral forms.
Icosahedral Symmetry - (adenovirus)
Helical Symmetry - (ebola)
Why is the enveloped virus more susceptible?
susceptible to chemical agents that can dissolve lipids
What is the benefit of the viral envelope?
facilitates attachment
How is a naked virus mediate attachment?
Viral attachment protein (VAP)
How is a naked virus released from the host cell? enveloped?
Naked - lysis
Enveloped - budding
What is an example of a complex virus?
poxvirus
What type of genome is in a helical (enveloped) virus?
ssRNA
What type of genome is in a helical (naked) virus?
dsDNA, ssDNA, ssRNA
What type of genome is in an icosahedral (enveloped) virus?
dsDNA, dsRNA, ssRNA
What type of genome is in an icosahedral (naked) virus?
dsDNA, ssDNA, dsRNA, ssRNA
Which capsid type only contains ssRNA?
helical enveloped
Which capsid type has all four genomes?
icosahedral naked
Which capsid type has both DNA genomes but only ssRNA?
helical naked
Which capsid type has both RNA genomes but only dsDNA?
icosahedral enveloped
What factors affect tropism?
- Can the virus get into the host cell?
1a. - can use more than one receptor to gain entry into one type of host cell
1b. -can use the same receptor to gain entry into many different cells - If it enters cell, is the appropriate machinery available. Host cell must be in a stage for replication.
- After replication can the infectious virion get out and spread infection?
What are the 5 common routes of viral transmission?
Blood and bodily fluids Insect bites Respiratory GI Direct Contact
What are examples of viruses that spread via blood and bodily fluids?
CMV EBV HBV HCV HIV
What are examples of viruses that spread via insect bites?
Dengue
EEEV
WEEV
West Nile
What are the examples of viruses that spread via respiratory droplets?
Small - influenza, measles, smallpox, VZV
Large - adenovirus, parainfluenza, parvovirus, smallpox
Direct contact via respiratory secretions: RSV, rhinovirus
What are examples of viruses that spread via GI?
enteric adenovirus, HAV, Norwalk virus, polio, rotaviruses
What are examples of viruses the spread via direct contact?
HSV, smallpox, VZV
What are three routes for viral spread?
hematogenous spread
neural spread
multiple pathways for spread
Describe three ways that hematogenous spread occurs in the bloodstream.
Freely - enterovirus, HBV, togavirus
associated with RBCs - Rift Valley Fever, Colorado tick fever
associated with lymphocytes of monocytes - CMV, EBV, HIV
Describe how virus spreads to the neural system?
entry can be via receptors near synaptic endings, motor neurons, sensory neurons, infection of Schwann cells, olfactory system rod processes
-HSV, rabies, VZV
Describe what is meant when a virus spreads via multiple pathways.
The virus utilizes different pathways at different stages of the infectious cycle.
Infects one way and spreads another
VZV - skin via hematogenous spread; neuronally for latency and reactivation
What are the three steps for cell entry by a virus?
Attachment to cell receptors
Penetration of the host cell membrane by fusion protein
Merging of the viral envelope and cell membrane
What are the 6 steps for viral multiplication?
- attachment/adsorption
- Penetration/entry
- Uncoating/release of nucleic acid from capsid
- Replication
- Assembly
- Release
How does viral titer change over 1 infectious cycle?
Titer is stable during periods of attachment.
Titer decreases during disassembly, transcription, translation, and genome replication (Eclipse phase). Infectivity of virus is lost as it uncoats.
Titer increases as progency virions are assembled and infectious.
(Chart)
Where does RNA virus replicate? What is the exception?
RNA»_space;>cytoplasm
influenza»_space;>nucleus
Which RNA protein synthesis is the most rapid?
ss + RNA (poliovirus, West Nile)
-no need to use RNA polymerase to make a strand before replication
Which two RNA virus types use RNA polymerase?
ss -RNA (influenza, measles) ds RNA (rotavirus)
Which virus type requires a viral reverse transcriptase and used the Host RNA polymerase?
retrovirus (HIV)
Which DNA virus uses a viral reverse transcriptase for genome replication?
Hepadnavirus
Where do DNA viruses replicate? What is the exception?
DNA»>nucleus
pox»>cytoplasm
Whose RNA polymerase is used in DNA viral protein synthesis?
Host RNA polymerase
Which DNA virus type uses host or viral DNA polymerase for genome replication depending on virus type?
dsDNA - HPV (circular)
-herpes (linear)
What two types of transcription do most DNA viruses undergo and what is being produced during each one?
early - regulatory proteins and those necessary for DNA replication
late - structural proteins
Describe an acute infection and give an example.
Acute - steep curve, undergoes multiple rounds of reproduction resulting in death of host cell, lytic
polio
influenza
Describe the outcome of a chronic viral infection and give an example.
Chronic - flatter curve and continuing source of infection
Virus undergoes replication and shedding that continues after acute illness ends.
+/- symptoms and cell injury
Localized: Warts, Papillomaviruses
Systemic: RNA virus (HIV, HCV) DNA virus (Hep B)
Describe the outcome of a latent viral infection and give an example.
No viral synthesis until signaled by stimuli
Genetic material may:
-incorporate into host cytoplasm (herpesvirus)
-incorporate into host genome (retrovirus, HBV)
-DNA virus or retrovirus
Sometimes latent outcomes can be transforming. What might occur?
- malignancies due to differentiated host cell
- invasive growth due to loss of contact inhibition
- benign or cancerous (EBV, HPV 16/18, HBV, HTLV1/2)
Compare local vs. systemic infection.
local - infection restricted to site of virus entry
systemic - spread to underlying tissue and lymph node
Which DNA viruses are nonenveloped?
parvovirus (ss linear)
adenovirus (ds linear)
papillomavirus (ds circular)
polymaviruses (ds circular)
Which DNA viruses are enveloped?
herpesvirus (ds linear)
poxvirus (ds linear)
hepadnaviruses (ds circular)
Which RNA viruses are nonenveloped?
astrovirus (ss +sense)
callicivirus (ss +sense)
piconaviruses (ss +sense)
reovirus (ds)
rotovirus (ds)
Which RNA viruses are enveloped?
togavirus (ss +sense)
flavivirus (ss +sense)
coronavirus (ss +sense)
rhabdovirus (ss -sense linear)
paramyxovirus (ss -sense linear)
arenavirus (ss -sense segmented)
bunyavirus (ss -sense segmented)
orthomyxovirus (ss -sense segmented)
lentivirus (retrovirus)
oncovirus (retrovirus)
Which two RNA viruses are retrovirus?
lentivirus
oncovirus
Which three RNA viruses are -sense and segmented?
arenavirus
bunyavirus
orthomyxovirus
Which three RNA viruses are +sense?
togavirus
flavivirus
coronavirus
Which two RNA viruses are -sense and linear?
rhabdovirus
paramyxovirus
