Chapter 3: The Viruses Flashcards
By what characteristics are viruses classified?
- nucleic acid (DNA or RNA)
- arrangement of nucleic acid (single-stranded, double-stranded, +ve-sense, or -ve sense)
- structure of virus particle (Enveloped or non-enveloped)
- symmetry (helical, icosahedral, complex)
what is the function of the glycoproteins of a viral envelope?
help virus attach to receptor
what is the function of the matrix proteins of a viral envelope?
help attach capsid and envelope and keep them together
What is the difference between how enveloped and naked viruses are released from the host cell?
Enveloped viruses bud out, and do not kill the cell, whereas non-enveloped viruses exit by cytolysis.
What characteristic allows naked viruses to infect the GI tract?
they are resistant and survive in the outside world
By which routes can viruses be transmitted?
- inhaled droplets (e.g. rhinovirus, influenza viruses, MERS coronavirus)
- in food or water (e.g. hepatitis A virus, hepatitis E virus, noroviruses)
- by direct transfer from other infected hosts such as infected body fluids by sexual transmission or blood-borne routes (e.g. HIV, hepatitis B virus, Ebola virus)
- from bites of vector arthropods (e.g. yellow fever virus, West Nile virus, Zika virus)
To which receptor molecule does influenza virus attach in the host?
sialic acid receptor on lung epithelial cells and upper respiratory tract
To which receptor molecule does rabies attach in the host?
ACh receptor; neuronal cell adhesion molecule
To which receptor molecule does HIV attach in the host?
CD4: primary receptor
CCR5 or CXCR4: chemokine receptors
(HIV requires presence of both receptors)
To which receptor molecule does Epstein-Barr virus attach in the host?
CD21 (also called CR2) receptor on B cells
What is the eclipse phase?
The stage during which the viral envelope and/or the capsid are shed and the viral nucleic acid released into the cytoplasm after fusion of viral and host membranes, or uptake into a phagosome. The virus is now not infective until new complete virus particles reform after replication.
Describe the order in which viral proteins are transcribed.
Enzymatic proteins usually transcribed early (proteins forming RNA polymerase then genes coding for proteases) then capsid are late genes needed to put virus particles back together are transcribed after
Which glycoproteins replace all other membrane proteins prior of release of enveloped influenza RNA virus by budding through host cell membrane?
hemagglutinin and neuraminidase
Describe lytic infections
In lytic infections, the virus goes through a cycle of replication, producing many new virus particles (influenza)
Describe persistent infections
In persistent infections, the cell may remain alive and continue to release virus particles at a slow rate (hepatitis B) which could result in a symptomless carrier of the virus.
