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Micro/Immuno Part 2 > Virus Life Cycle > Flashcards

Flashcards in Virus Life Cycle Deck (26):
1

infected cells

-cytopathic effects
-viruses not visible by light microscopy
-infection may cause CPE that can be used to study virus replication and infectivity
-not all viruses cause this

2

key concepts about viruses

-obligate intracellular
-no genes for biosynthetic pathway-protein/lipid synthesis
-assemble from host cell molecules
-evolve rapidly compared to host

3

overview of replication

virus needs:
-right host (tropism)
-cells with right receptors (susceptible)
-appropriate intracellular environment (permissive)
-biosynthesis machinery
-abundant building blocks-nt (RNA and DNA), amino acids, ATP, lipids, sugars
-time to finish replication

4

steps in virus replication

1. recognition of target cell
2. attachment
3. entry-penetration or fusion
4. uncoating
5. transcription of mRNA
6. protein synthesis
7. replication of the genome
8. assembly of virions
9. egress-lysis, budding, exocytosis

5

steps 1 and 2

-recognition and attachment
-recognition is interaction between virions and tissues-sensing the environment
-attachment is binding of virion surface to its specific cellular receptor

6

host range

-the preferred species

7

tissue tropism

-preferred cell type

8

susceptible

-cells that a virus can enter
-have specific receptors

9

permissive

-cells that support virus replication and virion synthesis

10

abortive infection

-replication is incomplete

11

step 3

entry
-virions may use multiple routes to enter cells
-varies by cell type
-may have consequences for disease outcome
-penetration
-fusion

12

penetration

-engulfment of entire virion into cell
-receptor mediated endo
-pinocytosis
-phagocytosis

13

fusion

-virion envelope fuses with PM, leaving parts of virion behind

14

step 4

uncoating
-release of genome into cell
-for infection to begin, capsids must open to release genome into the cytoplasm or nucleus
-marks the beginning of the eclipse phase
-direct penetration or membrane fusion
-can uncoat at PM or within endosomes or at nuclear membrane

15

step 5

transcription of mRNA
-all viruses must make mRNA
-viral genome is template for transcription
-viral and host transcription factors regulate mRNA synthesis
-mRNA is made by viral or host polymerases

16

DNA vs RNA viruses

-DNA can go to transcription then translation
-RNA viruses need RDRP to make copies of RNA for transcription

17

step 6

protein synthesis
-viral mRNAs are translated into protein by the host machinery-ribosomes, tRNAs, amino acids
-viral proteins are sorted to 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
-then the virion is assembled

18

step 7

replication of the genome
-viral genomes come in many types-ss/ds RNA/DNA, + or - sense, linear, circular, segmented, sealed ends
-polymerases make new genomes using host cell nts
-RDRP, viral DNA pol, host DNA pol, Host RNA pol II

19

DNA viruses

-use viral or host DNA pol (for replication)
-use host RNA pol II (for transcription)

20

RNA viruses

-use RDRP to make mRNA and genomes (for replication and transcription)

21

step 8

virions assemble
-capsid proteins usually made late in infection
-icosahedral and helical capsids self assemble
-complex capsids are made of genomes coated with nucleoproteins
-some capsids mature outside the cell
-envelopment
-end of eclipse phase

22

virion envelopment

-enveloped viruses acquire a membrane from a cellular source-ER, Golgi ,PM
-viral and cellular proteins are sorted to site of envelopment-membrane through secretory and cytosolic next to membrane

23

assembly with envelopment

-capsid assembly can occur at the same time as envelopment
-all virion components accumulate at the site of capsid formation, genome incorporation, matrix, glycoproteins, and envelope

24

step 9

egress of virions
-budding
-exocytosis
-lysis
-cell to cell spread
-may transfer to new cells by fusion--> syncytium (multinucleated cell)

25

single step virus growth curve

-eclipse- no virus is recovered during the replication and assembly phases
-maturation and release- virus particles are made and can infect other cells
-burst size- number of infectious viral progeny from a single round of replication
-see graph

26

cell lysis

-produces virus plaques
-lysed cells appear clean when cell monolayers are stained with dye
-infectious virions are measured in PFUs- plaque forming units