Lecture 2 Flashcards
What are the 10 Virus replication phases?
Attachment Penetration Uncoating of viral material Transcription of mRNA Translation of early proteins Replication Transcription of mRNA Translation- late proteins Assembly of virions Release of virus from cell
How does the herpes virus acquire its envelope?
Different viruses acquire their envelope from different membranes in the host cell: cytoplasmic membrane, nuclear membrane, ER membrane. As the virions are being assembled, they move toward the membrane that is required (determined by the virus). The virus envelope is essentially a modified cell membrane, meaning that the host cell’s membrane becomes modified by the insertion of virus-encoded proteins during the replication process.
Ex. herpesvirus acquires an envelope during the budding process (release from the cell), therefore the envelope is a modified cytoplasmic membrane.
What is the envelope?
modified host cell membrane that contains the anti-receptors to recognize host cell receptors,
mediates the attachment phase of viral replication
What is the difference between anti receptor and receptor?
The anti-receptor is a 3D structure on the virus (the anti-receptor is a region on the HA peplomer), whereas the receptor is a 3D structure on the host cell.
4) Describe the significance of sialic acid-galactose linkages of cell receptors with respect to species specificity of influenza viruses.
The influenzavirus HA anti-receptor recognizes/binds to sialic acid residues on the host cell receptor.
Cell receptors of various species contain sialic acid and galactose that are linked to one another by different conformations. Species specificity is due in part to the distribution of cells with these different linkages throughout the host.
For example, α-2,3 linkages are found in avian receptors. α-2,6 linkages are found in mammalian receptors. The variation in linkages causes slightly different conformations of the host cell receptor- these changes are recognized by the viral anti-receptor and contributes to species specificity of influenzaviruses (there are other factors that also help determine host range).
What is the viral capsid?
protein structure that protects the viral genome
may be enveloped, non-enveloped, depending on the virus family
What is viral symmetry?
refers to the geometrical relationship between the capsid and genome
two types icosohedral or helical
What is icosohedral symmetry?
NA loosly contained within a polyhedron that has either 5,3, or 2 fold axis of rotation
What is helical symmetry?
capsid is closely associated, sometimes directly attached to the NA,
looks like a herringbone on EM
What is the difference between a capsomere and a protomere?
protomer is the basic structural component of the viral capsid, whereas a capsomere is simply a morphological unit that can be clearly discerned by EM
What is a protomere?
described as being the basic building block of the capsid, formed by distinct polypeptides
What is a capsomere?
The term capsomere is sometimes referred to as the basic structural unit of the capsid, but this is incorrect (the protomer is the basic structural unit). For some viruses, the protomers are arranged in a manner that form clearly distinct morphological units, therefore the protomer also constitutes the capsomere. The capsomere may be made up of a single protomer, or of several protomers coming together
T/F
The protomer is always the basic structural unit, and may or may not also be the basic morphological unit (capsomere)
TRUE
What are structural proteins function, give an exapmple?
Structural proteins are matrix proteins that provide support for virus envelopes.
Ex. rhabdoviridae (rabies, vesicular stomatitis virus) – matrix protein contributes to the rigid structure of the virion
-influenzavirus – the matrix protein provides a basis for glycoproteins that are associated with the envelope to bind and stabilize – this may contribute slightly to the shape of the virion.
What are structural proteins function, give an exapmple?
Non-structural proteins do not contribute to virion structure and instead function as enzymes or regulatory proteins.
Ex. influenzavirus: three nonstructural proteins comprise the polymerase complex: PB1, PB2, PA.
-poxviruses: have several proteins that are virokines/viroreceptors that function to suppress the host immune response.
Virokines: the counterpart of cytokines that belong to the virus. These can mimic host cell cytokines and may play a role in suppressing the host immune response.
Viroreceptors: bind to interferons sent out by dying host cells and interfere before they can reach their intended target (their target is usually other host cells – they want to bind and stimulate and antiviral state as a defense mechanism).
-rotavirus: Non-structural protein 4 (NSP4) acts as an enterotoxin and contributes to the diarrhea caused by rotaviruses
Draw & accurately label a diagram of influenza virus, and describe the function of the proteins and what proteins are used for classification at the “type” and “sub-type” levels.
DO IT but i doubt this is on the test bc its on the computer
Define Nucleocapsid protein (NP)
internal protein that forms the nucleocapsid.
*used for type classification (ex. type A, B, C)
Define Matrix protein 1 (M1
internal protein that stabilizes the virus envelope (may contribute to virion structure).
*used for type classification (ex. type A, B, C)
Define Hemagglutinin (HA)
envelope glycoprotein that contains the antireceptor region.
There are 16-17 antigenically distinct HA proteins.
*used for subtype classification (ex. H1N1).
Define Neuraminidase (NA)
envelope glycoprotein.
There are 9 antigenically distinct NA proteins.
*used for subtype classification (ex. H1N1).
Define PB1, PB2, PA
nonstructural proteins that form the polymerase complex
10) Describe how nomograms are used to name specific influenza virus isolates.
Nomograms describe individual influenza virus isolates based on their type, host species, location, date, and subtype.
Ex. If a type A, subtype H1N1 influenza virus was isolated from a pig in Iowa in the year 2015:
A /swine /Iowa /2015 /H1N1
What does strandedness mean?
Strandedness – single vs. double vs. 2 strands covalently linked. This characteristic of viruses is important in understanding how they replicate and which cells they might infect, etc.
Give an example of how stranded effects virus? Parvo Virus
Parvoviruses are very small single-stranded viruses. Because they are single-stranded, they cannot be transcribed directly by cellular transcriptase. They are very small viruses and therefore do not carry their own polymerase – they rely on the host cell machinery for this. They tend to infect host cells that have a high mitotic index (rapidly dividing cells) because if the virus happens to be in a cell that is starting to undergo division, there is going to be a lot of DNA-dependent DNA polymerase (the host cell uses it to replicate its own genome). This cellular DNA-dependent DNA polymerase can use the single strand of viral DNA to generate a template to make a double strand, which can then be expressed and used to replicate the virus.
What is configuration?
c. Configuration – the genome can take on different configurations (e.g. linear, circular, segmented) that can play a role in determining viral features.
How does configuration effect replication?
i. Ex. influenzaviruses have a segmented genome, which is a huge factor in antigenic shift and the emergence of new subtypes. Genetic reassortment is possible with the segmented genome, resulting in progeny viruses having different combinations of genetic segments donated by the two parent genomes. Each new subtype has potential to cause an outbreak of pandemic proportions and requires a new vaccine
