MCM 2-2 Virus Life Cycle Flashcards Preview

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Flashcards in MCM 2-2 Virus Life Cycle Deck (19)
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The 5 requirements for virus replication

1. Right host/host range (tropism)
2. Cells with right receptors (susceptible)
3. Appropriate intracellular environment for virus replication/virion synthesis (permissive)
4. available biosynthesis machinery from the host
5. abundant building blocks (RNA, DNA, Amino Acids)


General Steps of Viral Replication

1. recognition of target cell
2. attatchment
3. entry (penetration or fusion)
4. uncoating (elipse begins)
5. transcription of mRNA
6. protein synthesis
7. Replication of Genome
8. assembly of virions (eclipse ends)
9. egress (budding, lysis, exocytosis


describe the 2 ways of viral entry into host cell

penetration - engulfment of entire virion into cell (receptor-mediated endocytosis, pinocytosis, or phagocytosis)

Fusion - virion envelope fuses with plasma membrane, leaves portion of virion behind


describe the uncoating stage

uncoating begins the eclipse phase

release of genome into cell, capsid must open to release genome into cytoplasm or nucleus for infection to begin


describe the transcription of viral mRNA

the viral genome is the template

viral and host transcription factors regulate mRNA synthesis

mRNA is made by viral or host polymerases


describe viral protein synthesis

viral mRNA's are translated into protein by the HOST machinery (ribosomes, tRNA's, amino acids)


where are viral proteins sorted?

to the site of virion assembly

capsid proteins interact with newly made genomes

membrane proteins traffic through the secretory pathway

cytosolic proteins accumulate next to the membrane


Describe the diversity that exists in viral genomes

can either be RNA or DNA that is ds or ss, + or - sense

can be linear, circular, segmented, sealed ends, etc..


_________ polymerases make new genomes using _______

Host or Viral Polymerases make new genomes using host cell nucleotides


describe the polymerases involved in making new viral genomes

1) Viral RNA-dependent RNA polymerase (RDRP) (used by RNA viruses)

2) Viral DNA polymerase (used by DNA viruses)

3) Host cell DNA polymerase (used by DNA viruses)

4) Host cell RNA Pol II (RNAP II) (used by RNA viruses to make mRNA and genomes)


when does the eclipse phase end?

during assembly of virions, when the capsid proteins form an empty shell


describe the assembly of virions

this ends the eclipse phase

1. capsid proteins form an empty shell late during infection

2. envelopment


describe when and how capsid proteins form an empty shell

Icosahedral and helical capsids self assemble

complex capsids are made from genomes coated with nucleoproteins

some mature outside of the cell


describe envelopment

-acquire membrane from cellular source (ER, golgi, PM)
-viral/cellular proteins sorted to site of envelopment
-membrane proteins through secretory pathway
-cytosolic proteins accumulate at membrane

-concerted assembly with envelopment can also occur (capsid assembly occurs at the same time) - all virion components accumulate at the site of capsid formation, genome incorporation, matrix, glycoproteins, and envelopment


describe the two types of virion egress

1. for cell-associated virions (cell-cell spread, cell fusion/syncytium formation)

2. for virions released into extracellular space (lysis, budding, exocytosis)


The phases of single step virus growth curve

1. eclipse phase - no virus recovered during the replication/assembly phases
2. maturation and release phases - virus particles are made and can infect other cells


what is the burst size?

the number of infectious progeny from a single round of replication


describe the appearance of cell lysis in viral culture and how this is measured

viral plaques

virus egress lyses cells
lysed cells appear clear when monolayers are stained
infectious virions are measured in PFU's (plaque forming units)


exocytosis of envoloped virions occurs in a burst and lyses the cell (TF)


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