Viro - Lecture 2

drraythe's version from 2015-08-30 15:35


Question Answer
how do we study the replication of viruses?studied using cell cultures (in suspension or monolayer, ie a single layer of cells on the bottom of a petri dish). CAN ONLY BE IN VITRO, NOT IN VIVO. infectious clones are used for unculturable viruses. all cells are infected simultaneously using a high multiplicity of infection, all cells are infected simultaneously using a high multiplicity of infection.
what is the eclipse period? The eclipse period: after penetration the virus cannot be detected for hours (2-12 hrs) until the first progeny of virions become detectable (unrelated to the incubation time of the virus)
what is the incubation period?not time virus is in cell, its time in animal before it shows clinical signs
order of events in which a virus infects a cellattachment--> penetration--> uncoating--> transcription--> translation--> replication
what is translation? RNA->prot
what is transcription?RNA--> to diff RNA genomic message (or DNA->RNA)
what is replication? DNA--> DNA or RNA-->RNA
early gene products do/are what?include proteins which--- shut down cellular processes, regulate expression of viral genome, enzymes required for replication of viral nucleic acid
late gene products do/are what?usually structural proteins
gene products of the virus replicating tend to come out in a certain order. what are some early products and what are some late productsEarly gene products include proteins that shut down cellular processes, proteins that regulate the expression of the viral genome, and enzymes required for the replication of the viral nucleic acid. Late genes are usually structural proteins
DNA viral replication (where and what enzyme)Most DNA viruses replicate in the nucleus. These use cellular DNA dependent RNA polymerase II to transcribe their DNA
RNA viral replication (where, and what enzyme)Most RNA viruses replicate in the cytoplasm, and cells don’t have an enzyme to copy RNA from an RNA template; therefore their nucleic acid has to either function as a mRNA or the virus must carry its own viral RNA dependent RNA polymerase to transcribe RNA from an RNA genome
what are the two cellular enzymes involved in replication? (1) DNA dependent DNA polymerase (2) DNA dependent RNA polymerase
what are the three viral enzymes involved in replication? (1) RNA dependent DNA polymerase (retrotranscriptase) (2) RNA dependent RNA polymerase (RNA viruses) (3) DNA dependent RNA polymerase (DNA viruses which replicate in the cytoplasm)
what enzyme does a retrovirus use?(viral) RNA dependent DNA polymerase
what enzyme does a DNA virus use?(cellular, except for pox it's viral) DNA dependent RNA polymerase
what enzyme does a RNA virus use?(viral) RNA dependent RNA polymerase
how does a virus attach?aka Viral Adsorption: receptors on the viral envelope or capsid become connected to complementary receptors on the cell membrane
how does a virus penetrate? (entry 3 diff ways)(1) membrane fusion (2) endocytosis (3) genetic injection
explain entry of virus via membrane fusion (which type of virus usually does this?)Viral receptors attach to the receptors on the surface of the cell and secondary receptors may also be present to initiate the fusion with the host cell. The virus's envelope blends with the cell membrane, releasing its contents into the cell. Enveloped viruses usually enter this way
explain entry of virus via endocytosis (which type of virus usually does this?)This is a receptor mediated process. Most naked viruses use this process.
explain entry of a virus via genetic injection (which type of virus usually does this?)injecting only its genome into the cell, leaving the rest of the virus on the surface, for example phages
how can a virus usually get to the nucleus?they have a cellular chaperone get them in
DNA viruses that replicate in the nucleus use what enzyme to replicate?cellular DNA-dependant RNA polymerase II to produce their mRNAs
DNA viruses that replicate in the cytoplasm use what enzyme to replicate?they carry a DNA-dependant RNA polymerase of their own (which has the same function as the cellular enzyme but is localized in the cytoplasm)
SS+ RNA viruses replicate how, and using what enzyme?In most SS+ RNA viruses the nucleic acid can directly bind to ribosomes and start translating either partially or fully. Some are capped and have polyA tails! They look and behave as cellular mRNAs. Once they translate the mRNA they usually code for their own viral polymerase to replicate their genome (a specific RNA-dependent RNA polymerase)
SS negative sense RNA viruses replicate how and using what enzyme?SS negative sense RNA viruses must carry their own enzyme inside their nucleocapsid, a specific RNA-dependant RNA polymerase (the protein itself not just the gene)
what is diagnostic of the POX virus replication?pox has significance bc leaves inclusion bodies in cytoplasm which are diagnostic!! brings its own enzymes
pos stranded RNA viruses disguise themselves to look like what?mRNA (so dont have to go into transcription, can go straight to translation.)
which type of virus can do translation first?RNA (ss+)
retroviruses consist of what?2 copies of ss+ RNA but they replicate through a DNA intermediate
which enzyme does a retrovirus use? how?(RNA dependent DNA polymerase) They carry a reverse transcriptase that uses a tRNA molecule as primer making a ss DNA copy. Same enzyme then acting as a ribonuclease, removes the parental RNA from the RNA:DNA hybrid. Then copies the negative sense ss DNA to form a linear ds DNA which contains an additional sequence LTR (long terminal repeats) at each end. This ds DNA then circularizes and integrates into the cellular chromosomal DNA. Transcription of viral RNA occurs from this integrated (proviral) DNA.
what is an LTR and what is its purpose?long terminal repeat-- it is the part of the linear DS DNA which was made by the retrovirus which allows the virus to insert its genome into the hosts genome so the host will make proteins for it
how retroviruses work, in my words....two ss+ RNA strands go into the cell. they carry a reverse transcriptase to make a ss DNA copy of one of the strands. then the reverse transcriptase is used to make the other strand of DNA off the first strand of DNA. the DNA made also has LRT (long terminal repeats) which allow the DNA to be inserted into the host genome so the host genome can make proteins for the virus.
what is proviral DNA?DNA of the virus's (usually retrovirus) which is inside the host genome so that the host unknowingly copies of the virus proteins
what is the difference between cellular mRNA and viral mRNA?Cellular mRNA are monocistronic (1 message= 1 gene) but viral mRNA can be polycistronic (1 message = many genes)
what is monocistronic? polycistronic?mono= one message one gene. poly= one message many genes
The structural proteins of simple icosahedral viruses do what once they are made?they associate spontaneously to form capsomers which self-assemble to form capsids into which the viral nucleic acid is packaged
assembly and release of helical structured viruses?In helical structured viruses, the RNA molecule self-assembles as a cylindrical helix bound to their structural proteins (think of a pearl necklace)
how are naked viruses released from the cell?Naked viruses accumulate in the nucleus or the cytoplasm until they exit from the cell by lysis
how do enveloped cells exit the cell?BUDDING OR EXOCYTOSIS
do retroviruses have double stranded RNA?no, they have diploid ss+ RNA (not DS bc not complimentary)
family of virus suffix-viridae