Viruses Flashcards
T/F: Virus has DNA and RNA.
False: Has either or, not both usually.
True: Mimivirus.
Define Virion.
Mature infectious virus particle.
Define Capsid.
Protein shell that encloses and protects the viral nucleic acid.
Define Nucleocapsid.
T/F: Not all viruses have this.
Nucleic acid and closely associated capsid proteins.
True.
Define Envelope. What are the 3 components?
Viral membrane, consists of:
1) Lipid bilayer
2) Proteins
3) Glycoproteins
What are the 7 types of classification?
1) ds DNA
2) ss DNA
3) ds RNA
4) ss RNA +strand
5) ss RNA -strand
6) RNA viruses require a DNA intermediate for replication
7) ds DNA using reverse transcriptase
+ ss RNA acts as _____ RNA in host cell.
messenger RNA. enters and make protein right away.
All forms of DNA must make +ssRNA to be virulent. Genetic material is infectious on its own.
How does +RNA replicate?
Make -RNA and then +RNA.
What are the 3 topologies of Capsid?
1) Complex - Poxvirus
2) Icosahedral - Solid with faces, vertices and fold symmetry
3) Helical - Like alpha helix morphology.
Adenoviral has what topology?
Icosahedron with spike proteins (penton). It does not have membrane, naked and encloses the genome.
What are Matrix (M) Proteins?
Found associated with inner layer of envelope. Aid in viral structure.
What are Fusion (F) Proteins?
Found on envelope surface. Cause viral membranes to fuse with cellular membranes. This is so virus can enter host cell.
T/F: Noneveloped viruses are more resistant to disinfect than enveloped viruses.
True.
Lipid membranes are easier to disrupt, but they are essential for virus to replicate.
What are the 5 physiochemical classification of human viruses?
1) Chemical nature of nucleic acid.
2) Nucleic acid sequence similarities.
3) Presence of envelope.
4) Dimensions of virion and capsid.
5) Symmetry of nucleocapsid.
What are the 4 steps of viral infection?
1) Attachment to host cell.
2) Entry
3) Synthesis of viral proteins and genome.
3) Assembly and release.
What is the most important determinant of host specificity?
Presence of viral receptors on cell surface.
Are viruses host specific?
YES! Very, and can be tissue specific due to presence or absence of a receptor.
What receptor is present for HIV-1 and on what cell?
CD4 receptor on macrophages and t-cells. HIV-1 antigen normally binds to MHC class II mediates t-cell response.
What are the 2 coreceptors for HIV-1 that are normally chemokine receptors present on what cells?
Cxcr5 and Ccr5. On immune cells.
How does nonenveloped viruses enter?
1) Rearrange capsid protein.
2) Viruses engulfed by receptor mediated endocytosis. Partial breakup of capsid in the vacuole. Then migration into cytoplasm for further uncoating.
How does enveloped viruses enter?
1) Fusion of viral membrane cell membrane by viral F protein.
2) Phagocytosis and fusion of viral membrane with membrane of phagosome mediated by a viral F protein.
How does F protein work?
Has hydrophobic domain that can insert into the host cell membrane.
T/F: HIV is enveloped.
True
Cxcr4 is coreceptor for what cell?
Ccr5 is coreceptor for what cell?
Cxcr4 - T-cell tropic strains
Ccr5 - Macrophage-tropic strains.
What is the mechanism for HIV-1 binding and membrane fusion?
1) SU binds to CD4
2) Exposes Cxcr4 or Ccr5, depending on which cell it wants to fuse with.
3) Su binds to Cxcr4 or Ccr5
4) Causes conformational change of TM
5) F protein at the end of TM fuse with membrane of desired host cell
How can an individual be resistant to HIV-1 infections?
People who are homozygous for deletion in Ccr5 are resistant to infections.
What is the Eclipse period? What is the Latent period?
Eclipse: nucleic acid uncoated from protective capsid.
Latent: no extracellular virus can be detected.
What are the 2 mechanisms for assembly and release of virus?
1) Disintegration of infected cell (BURST). This is for naked nucleocapsids.
2) Slow release - acquire envelope as the nucleocapsid buds through a virus modified cellular membranes.
What are the 3 structural units of virion protein shells?
1) Individual polypeptides.
2) Polyprotein precurser.
3) and/or Chaperone mediated.
What are the 4 cytopathic consequences of viral infection?
Examples.
1) Rouding, Cell death/lysis - POLIOVIRUS
2) Transformation - proliferate. cells piling on top of another.
ROUS SARCOMA VIRUS CHICKEN CANCER
3) Syncytia - fusion of membranes of adjacent cells. forms mutinucleated giant cells.
MURINE LEUKEMIA
4) Inclusion bodies - HSV (cowdry type A) and Rabies (negri bodies)
What are the 2 Enumeration of viral particles?
1) Electron microscopy
2) Hemagglutinin - Viruses bind to RBC and make lattice preventing RBC from falling to bottom of tube.
What are the 2 Immunological means to observe virus products?
1) Complement Fixation - Virus antibody complex activate and consume the complement. Unable to lyse RBC.
2) Direct fluorescent antibody - antibody binds to virus.
Complement Fixation.
When correct antibody binds to antigen, then complement can bind to the complex INSTEAD of lysing the RBC. Free complement will lyse RBC.
Define Western blot.
Viral proteins run on gel and visualized by antibody.
Define ELISA.
Enzyme linked inmmunosorbant assay. Antibody binds to viral products.
How does antibody neutralize (3 ways)?
1) Hinder absorption to cells.
2) Stabilize virus capsid, prevents uncoating
3) Inhibits membrane fusion and entry into cells.
