Micro 8 Flashcards
What are the four types of viral RNA structure?
+ssRNA, -ssRNA, dsRNA, and circular -ssRNA
What are capsids?
proteins shells that hold viral nucleic acid
What are the main types of capsids?
helical, icosahedral, and complex
Describe helical capsids.
concerted assembly in which proteins of the capsid bind to nucleic acid as the nucleic acid alpha helix is being constructed (all happening at the same time). Proteins don’t spiral because they are bound to the alpha helix structure. Length of the capsid is determined by the length of the nucleic acid helix
Describe icosahedral capsids.
These are made in a sequential mechanisms known as headful packaging. Triangle shaped monomer proteins self-assembly to form pentamers and then those will self-assembly to form a pro-capsid, which has gaps for nucleic acid insertion. Following nucleic acid insertion, the mature capsid will form and seal. called headful because the size of the capsid is made to fit one genome inside. If the genome is too large, pressure will build and the capsid will burst
maximizes volume to surface area without internal support needed
What are naked viruses?
genome+ capsid= nucleocapsid is the final structure with no envelope. Commonly have spike proteins for attachment and are virulent in that form
What are enveloped viruses?
Some viruses have lipid envelopes that are derived from cellular membranes so the nucleocapsid is not the infectious portion. Loss of the lipid envelope causes loss of infectious nature. In the envelope, the protein content (typically glycoproteins) are encoded by the virus themselves and inserted in the envelope. These mediate virus attachment and integration, so the loss of the envelope is bad for the virus.
never stable in GI and require a wet environment for spread
What are the main steps of virus replication?
1) attachment and penetration
2) uncoating
3) early transcription and synthesis of nonstructural proteins (for DNA and RNA viruses)
4) genome replication
5) late transcription and synthesis of structural proteins
6) assembly and release
What are the two main ways viruses enter cells?
endocytosis (ph-dependent) and plasma membrane fusion (ph-indepedent)
How does viral endocytosis work?
Enveloped virus (most naked viruses use this route) attaches to the surface via spike proteins and invaginate into the cell in an endosome. As the endosome matures from an early to a late endosome, the pH lowers, triggering conformational changes in the protein coat of the virus and it fuses with the endosome, releasing the nucleic acid into the cell.
How does plasma membrane fusion work?
pH-independent. Almost always used by enveloped viruses. Fusion glycoprotein in the envelope of the virus causes release of nucleic acid into the cell from the cell surface without the use of endosomes
What is early transcription?
transcription that occurs before genome replication and the point is to transcribe proteins that produce non-structural proteins (i.e. proteins needed for genome replication)
Where do RNA encoded viruses replicate?
the cytoplasms because they don’t need much from the nucleus
Where do DNA encoded viruses replicate?
the nucleus (with some exceptions)
What is late transcription?
transcription of structural proteins after genome replication
Naked viruses will then lyse the cell to be released. Enveloped viruses will likely bud from the cellular membrane which forms around it (so it derived from the host cell)
Remember: naked viruses will lyse the cell to leave
What is the eclipse period of viruses?
only occurs in viruses, not intracellular bacteria. From 2-10 hours at the start of viral infection where a virus cannot be detected inside or outside the cell.
At 2 hours all the virus has entered the cell and uncoated so that intracellularly we can’t detect the viral presence. At 10 hours after genome replication (at about 8 hrs) viruses produce/assemble the intracellular progeny virus and we can detect it.
When can viruses be detected extracellularly?
about 16 hrs when the progeny are released (the end of the latent period)
Latent period= time where viruses can’t be detected extracellularly
T or F. RNA viruses must encode their own RNA-dependent RNA polymerase
T. Because the template they are providing is RNA and we use a DNA template
Retroviruses must encode what?
reverse transcriptase (think HIV)
What is the difference between small and large DNA viruses in terms of DNA polymerase?
Small DNA viruses (HPV )do not have their own DNA polymerase because they are too small and can’t encode them so they use proteins that alter our DNA polymerase for their own use, while large DNA viruses (herpes) can encode their own (we can target these)
