Virus Replication and Genetics

Question 1

What are the nine stages of viral replication?

Answer 1

recognition, attachment, penetration, uncoating, transcription, protein synthesis, replication, assembly, lysis and/or release

Question 2

How does recognition of viruses occur?

Answer 2

receptor-ligand interaction: Viral asscociated proteins, found on nucleocapsid or membrane that bind to specific cellular receptors

Question 3

How does viral attachment occur?

Answer 3

binding of viruses via VAPs to their receptors: rabies viruses to NCAM in neuronal cells, EBV GP350 to CD21 on B cells, hemaglutinin on influenza A to sialic acid on epithelial cells, HIV GP41-GP120 to CD4 or CCR5

Question 4

How does viral penetration occur?

Answer 4

viropexis- small viruses slipping through the membrane, capsid must contain hydrophobic regions, all by chance (parvo, rhino, not very common); or membrane protein fusion (VAP bind receptor and viral membrane fuse with cell) or receptor mediated endocytosis (most)

Question 5

What is uncoating and what are the places this occurs?

Answer 5

important to note that viral RNA replicates in cytoplasm, viral DNA to the nucleus, at plasma membrane, in the endosome, sometimes only fully after a partial uncoating

Question 6

what happens with uncoating at the plasma membrane?

Answer 6

fusion of membrane or virus with host cell membrane, results in viral DNA or RNA being released to cytoplasm or fusion of two membranes results in viral capsid release into cytoplasm, enzymes in cytoplasm begin degrading capsid as it moves to nuclear membrane

Question 7

What happens when uncoating occurs in the endosome?

Answer 7

release of RNA to cytoplasm, capsids of DNA viruses partially degraded and upon lysis of endosome move to nucleus for complete uncoating

Question 8

When a full uncoating occurs following a partial uncoating how does this happen and what is released?

Answer 8

enzyme from nucleocapsid that further degrades nucleocapsid, either DNA or RNA that codes for the enzyme that facilitates further uncoating

Question 9

What is monocystronic?

Answer 9

each mRNA produces one specific protein

Question 10

What is polycystronic?

Answer 10

each mRNA produces multiple proteins in one single polypeptide chain, makes individuals by: start and stop codons or cleaving large protein into smaller proteins using virally or cellularly encoded enzymes

Question 11

What is monopartite?

Answer 11

all genes linked on a single piece of RNA or DNA

Question 12

What is multipartite?

Answer 12

distributed several pieces of RNA or DNA, make up whole viral genome, need the genome to be affective

Question 13

What is the significance of the polarity of RNA strands in viruses?

Answer 13

(+) can be read like mRNA by host ribosomes, (-) can NOT be read by host ribosomes

Question 14

What are the phases of transcription and translation in DNA viruses?

Answer 14

immediate early (proteins produced here promote cell takeover, shut down host processes), early (enzymes produced including DNA polymerase so genome replicated here), and late (structural proteins including viral capsids and glycoproteins)

Question 15

What happens after translation and transcription with DNA viruses?

Answer 15

capsid proteins migrate to nucleus, assemble into icosahedron and DNA packaged inside, viral glycoproteins inserted in ER and carbs attached, capsid buds through the modified membranes and transferred to Golgi, glycoprotein processed and virus buds (exocytosis) out of cell

Question 16

How do (+) RNA strand viruses replicate?

Answer 16

RNA attaches to ribosome, translated, 1st protein produced is RNA dependent RNA polymerase, complementary (-) strand synthesized as template for more (+) which acts as mRNA for proteins or is incorporated into nucleocapsid as nucleic acid

Question 17

How do (-) RNA strand viruses replicate?

Answer 17

not recognized by host ribosomes, RNA dependent RNA polymerase comes in as part of virus structure, capsid destroyed by cellular protease, RNApol acts on (-) strand (template) for (+) strand which is used for mRNA for proteins and more RNApol or template for more (-) strand

Question 18

How do retroviruses replicate?

Answer 18

virion w/ RNA dependent DNA polymerase (reverse transcriptase, RT), fuses w/ cell; RNA, RT integrase and proteins enter, RT + vRNA-> vDNA-> nucleus to integrate into host DNA, new vRNA used like hRNA-> viral proteins + vRNA= immature virion, matures via protease releasing viral proteins then buds out or can cause lysis (naked virion)

Question 19

What is recombination?

Answer 19

intramolecular genetic exchange between viruses or virus and host

Question 20

What is reassortment?

Answer 20

all genes go in and what comes out is different

Question 21

what is transcapsidation?

Answer 21

protein capsid of one strain but genome of another

Question 22

What is marker rescue?

Answer 22

lethal mutants can recombine with “helper” virus to supply missing genetic material such that lethal mutant is now viable; concern with live attenuated vaccines

Question 23

What are the four main phases that the 9 steps of viral replication can be sorted into?

Answer 23

early- virus recognize target, attach , penetrate and uncoat (time until genome replication); eclipse- starts w/ early pahse and goes until infectious virions appear intracellularly; Late- viral replication of genome through extracellular detection (protein synth, assembly and release); and latent- time of infection (cell entry) until extracellular virus is detected