Viral Structure & Replication Flashcards
Describe virus coat/capsid
lipid bilayer + glycoprotein
Describe nucleocapsid
nucleic acid + capsid
Describe nucleocapsid symmetry
Icosahedral (20 sides)
Helical
complex
Describe virus particle/virion
extracellular viral particle
Describe envelope-free viruses
nucleic acid + capsid protein
can be phaocytized
What is a virus?
a piece of genetic information that is capable of copying itself and may have a beneficial or detrimental effect
Describe tegument
matrix surrounding nucleocapsid
Explain routes by which viruses enter the body
inhaled droplets
food/water
bites or vector anthropods
direct transfer from infected host (sex, blood)
Most common forms of virus transmission
mucous membranes, broken skin
Explain key elements in virus infection of host cells including virus attachment/adsorption, virus receptors, host specificity and viral entry
-Cell receptors determine host specificity and tissue specificity
-attachment to a host cell depends on general intermolecular forces, then on more specific interactions between the molecules of the nucleocapsid in unenveloped viruses (or glycoprotein from a virus membrane in enveloped viruses) and the molecules of the host cell membrane
-Attachment to the receptor is followed by entry into the host cell
Penetration – all viruses can potentially enter by receptor-mediated endocytosis, a host-initiated process
Enveloped viruses may enter by membrane fusion or endocytosis followed by membrane fusion
Some viruses (ex: phages, polioviruses) inject the nucleic acid into cell, leaving the capsid outside (nucleic acid translocation)
What can prevent viral ligand from binding to receptor?
antibodies
Describe the difference between enveloped and naked viruses binding to the receptor
enveloped: use a glycoprotein
naked: use capsid protein
Amantidine, an influenza drug, aids in stopping the infection by…
interfering with acidification of the virion – preventing uncoating
Explain the process of virus replication including synthesis of virus mRNA, translation and processing of virus proteins, replication of virus nucleic acid and the assembly and release of virus particles
Attachment - viral ligand binds to receptor
Penetration - receptor-mediated endocytosis (enveloped may use membrane fusion or endocytosis)
Uncoating - naked viruses dissolve capsid
Gene Expression - viruses encode 1 long protein, 1 mRNA transcript, 1 promoter region, contains protease activity, self cleave at correct positions
Genome Replication - provirus is replicated by cellular DNA-dependent polymerase when host cell divides; cell must be in S phase
Assembly - nucleic acid binds capsid, glycoproteins are inserted onto cell membrane
Release - budding of enveloped virus, both enveloped and non-enveloped can be released via lytic cycle (lysis)
Compare and contrast the mechanisms by which dsRNA viruses, positive and negative sense ssRNA viruses and retroviruses synthesize mRNA and replicate genomic RNA
-In dsRNA viruses, one strand is first transcribed by viral polymerase into mRNA
-In ssRNA viruses, there are three distinct routes to the formation of mRNA:
- Ss has the positive sense configuration and same base sequence as that required for translation – can be used directly as mRNA
- The strand has negative sense configuration
- Must first be transcribed using viral polymerase into a positive sense strand, which can then act as mRNA
-retrtoviruses:
- positive sense ssRNA is made into a negative sense ssDNA using viral reverse transcriptase enzyme carried in the nucleocapsid
- dsDNA is then formed, which enters the nucleus and becomes integrated into the host genome
integrated viral DNA is then transcribed by host polymerase into mRNA
