4- Viral Classification Flashcards
What is a virus?
Viruses are obligate intracellular parasites that depend on the biochemical machinery of the host cell for replication.
What 2 things can’t the virus make outside of the host cell?
Proteins and energy
What type of genetic material does the virus contain?
DNA or RNA. Cannot be both
What is a virion?
virus particle consists of a nucleic acid genome packaged into protein coat (capsid) or a membrane (membrane)
What structure on the outer capsule of the virus mediates the interaction between the virus and the host cell?
Viral attachment protein (VAP)
What is the viral glycoprotein?
It is found in the surface envelope of enveloped viruses
Most viral glycoproteins have asparagine-linked (N-linked) carbohydrate and extend through the envelope and away from the surface of the virion, and take on the appearance of spikes on the virus surface
Most viral glycoproteins act as VAPs
Some act as enzymes
Glycoproteins also act as major antigens that elicit protective immunity
What is hemagglutanin?
hemagglutinin: is a glycoprotein that acts as a VAP on several different types of viruses (influenza, measles, mumps)
Hemagglutinin takes its name from the fact that it causes red blood cells to clump together
Hemagglutinin is antigenic
Hemagglutinin has two functions: it allows recognition of target cells, and facilitates the entry of the viral genome into the target cells by causing the fusion of host endosomal membrane with the viral membrane
Why must some viruses need an RNA-dependent RNA polymerease?
Cells in their natural uninfected state have no means of replicating RNA (they don’t need to)
The RNA virus genome must code for RNA-dependent RNA polymerases (replicases and transcriptases) that catalyze RNA replication
RNA is degraded quickly, so RNA-dependent RNA polymerase must be provided or synthesized soon after uncoating to generate more viral RNA
Otherwise, infection is aborted
What are the 9 steps of viral replication?
- Recognition of the host cell.
- Attachment
- Penetration (giggity)
- Uncoating
- Transcription
- Translation
- Replication
- Assembly
- Lysis and release
What is the latent period?
latent period: the period where the infectious virus cannot be detected because it is uncoated (lacks VAPs)
Includes eclipse period and ends with the release of new viruses
What is the burst size?
burst size: It describes the yield of infectious virus per cell (number of viruses released when the cell lyses)
What does endocytosis have to relate to viruses?
It is the means by which many viruses enter the cell, and is a normal cellular process
What is viropexis and what is the process?
It is the mode of entry for some smaller viruses: after the virus binds to the cell, hydrophobic structures on the capsid proteins are exposed, and allow the virus or viral genome to directly penetrate the membrane
What is syncytia formation?
Syncytia is virus-induced cell-cell fusion.
Some herpes viruses, retroviruses, and paramyxoviruses can induce cell-cell fusion to merge the cells of the host into multinucleated giant cells, or syncytia, which become huge virus factories.
This allows the virus to escape antibody detection and survive longer.
