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45 Cards in this Set
- Front
- Back
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What are the five steps of viral replication?
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Attachment and Entry
Genome replication -Processing of pre-mRNA -Translation -Intracellular Transport Assembly Exit/Maturation Virus growth cycle |
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What do viruses attach to on the host cell and with what, for replication?
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Binding to specific cellular receptors
-Glycoproteins -Carbohydydrate residues -More than one recpetor They are very specific to the species that they infect. |
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What is virus tropism?
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In many cases, the expression of receptors on the surface of cell determines the tropism of a virus:
-the type of host cell in which virus is able to replicate. |
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What are the two parts of viral entry in viral replication?
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Uptaking and Uncoating.
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What are the three parts of uptaking of viral entry during replication?
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TRANSLOCATION of the entire virion across the cell membrane
ENDOCYTOSIS (Receptor-mediated endocytosis ) of the virus into intracellular vacuoles; eventually into the cytoplasm. FUSION of the viral envelope with the cell membrane. |
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What is the uncoating process of viral entry during replication?
What is the mechanism? |
Release of viral nucleic acid from its protective protein coat or lipid envelope and allow viral gene for replication and transcription inside of the cell
Uncoating at the plasma membrane -Many enveloped viruses fuse directly with plasma membrane at neutral pH, and viral nucleocapsid is released directly into the cytoplasm Uncoating within endosomes Uncoating at the nuclear membrane |
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What is the function of viral receptor?
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Entry
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What part of the virus binds to the receptor on the cells?
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Glycoproteins on the capsid.
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How do DNA viruses replicate their genome?
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The DNA needs to get into the nucleus, there the DNA will rolling replicate and for each new loop of DNA produced, a capsid will come snatch it up. It's what she said.
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Which parts of the virus needs to be reproduced during virus replication?
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All parts of it the virion - the capside, the genome, the envelope (if the virus does that sort of thing).
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What is the viral replication process of dsDNA viral genome?
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mRNA is made from the coding strand, which is used to translate into the proteins necessary to turn off the host gene expression (transcription regulators), replicate the dsDNA (DNA polymerase, ribonuclease reductase, primase) and the structural units to make the capsid.
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What is the viral replication process of +ssDNA viral genome?
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Make the dsDNA from the one strand, then the mRNA and three kinds of proteins (for transcription regulators, replication proteins, and structural proteins). Instead of the dsDNA going into the capsids, they'll split into the + and - and the +ss will be packaged into the capsids.
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What is the viral replication process of +ssRNA viral genome?
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+ssRNA (in place of mRNA) codes for the three proteins (transcription regulators, replication proteins (mostly RNA dependent RNA polymerase), and structural proteins). To get more +ssRNA, the virus makes a -ssRNA in its mirror image for the replication proteins to work on to make all of the +ssRNA to be packaged into the capsids.
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What is RNA dependent RNA polymerase?
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RNA-dependent RNA polymerase (RdRP), (RDR), or RNA replicase, is an enzyme that catalyzes the replication of RNA from an RNA template. This is in contrast to a typical RNA polymerase, which catalyzes the transcription of RNA from a DNA template. This enzyme can go both from + to - and from - to +.
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What is the viral replication process of -ssRNA viral genome?
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These ones carry the RNA dependent RNA polymerase with them in their capsid, so it is ready to make +ssRNA that can be used as mRNA, to make the proteins (transcription regulations, replication proteins (RNA dependent RNA polymerase), and structural proteins) in order to make more -ssRNA for packaging into the capsids.
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How do dsRNA replicate?
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You can unzip the ds and use the +ssRNA as mRNA to make proteins.
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How do +ssRNA retroviruses replicate?
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First, they must use RNA-dependent DNA polymerase (get that? DNA polymerase) - also called reverse transcriptase, to make -ss DNA. The cell can make the +ssDNA with DNA polymerase. This dsDNA is integrated into the host genome to make +ssRNA (the major ones are gag, pol, env) from whenever the virus gets activated.
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How do gapped circular dsDNA genome of Hepadnaviridae replicate?
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This avian virus makes mRNA to make its proteins, the host cell makes -ssRNA and +ssRNA (just because that's what it does) made from the DNA, then through reverse transcriptase (produced from the mRNA) becomes -DNA and +DNA, to make double stranded for replication into new viruses.
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Where do viruses replicate inside the cells?
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DNA viruses in cytoplasm and nucleus. RNA viruses in cytoplasm. ?
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Which cellular compartment do most RNA viruses replicate in?
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cytoplasm?
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How do +ssRNA viruses transcribe?
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The most +ssRNA viruses binds directly to ribosomes and is translated without any prior transcription.
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How do DNA viruses that are replicated in the nucleus transcribe?
How do dsDNA viruses that replicate in the cytoplasm transcribe? |
DNA viruses that replicated in the nucleus: same as the cells. It is performed by cellular DNA-dependent RNA polymerase II.
The dsDNA virus replicated in the cytoplasm carry a DNA-dependent RNA polymerase. |
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How do dsRNA viruses transcribe?
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The dsRNA viruses have a specific dsRNA-dependent RNA polymerase.
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How do -ssRNA viruses transcribe?
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The –ssRNA viruses carry a specific ss RNA-dependent RNA polymerase.
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What is the post-transcription process for viruses?
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Similar to eukaryotic!
Splicing the intron from the primary transcripts to give rise to multiple ORFs (which was first shown in adenovirus transcription) Most virus mRNA has cap structure after processing, except flu virus RNA. Flu virus RNA cap is acquired by Cap Snatching the transcriptase of influenza virus also carries endonuclease activity, which cleaves the 5’-methylated caps from newly synthesized cellular RNA transcripts in the nucleus. |
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How do the host-cell dependent viruses, simple, "intermediate" and "complex", express their genes?
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Simple viruses: viral mRNAs must contain control signals which are recognized by the cell, e.g.: ribosome-binding sites, splice signals, polyadenylation signals
"Intermediate" viruses, e.g. Adenoviruses, encode their own DNA polymerase, but are still dependent on other cellular factors for replication. "Complex" viruses, e.g. Herpesviruses, encode a large number of proteins involved in DNA synthesis, and are largely independent of the cellular machinery. |
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How do non-segmented genome (RNA) viruses express their genes?
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Non-segmented genomes tend to produce polycistronic mRNA.
The polycistronic mRNA is translated into a polyprotein. Then the polyprotein is processed by proteolytic cleavage to form the mature gene products. |
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How do segmented genome (RNA) viruses express their genes?
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They are usually transcribed into monocistronic mRNAs.
One advantage of monocistronic mRNAs is that various proteins can be produced in different amounts, rather than in a constant ratio. |
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How does translation work for viruses?
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The viral mRNA translation (into protein) occurs in rough endoplasmic reticulum.
Polycistronic viral RNA is translated directed into a polyprotein: -It carries protease activity and cleaves the polyprotein at specific sites into several small proteins. Glycosylation of envelope protein: -occurs sequentially as the protein moves in vesicles: Newly synthesized proteins in rough endoplasmic reticulum move to the Golgi complex, and then to plasma membrane. |
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What are proteins encoded by viral genome?
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Structural proteins of virion
Virion-associated enzymes, especially polymerases (transcriptases) Regulatory proteins that control the temporal sequence of expression of the viral genome Proteins down-regulating expression of cellular genes Oncogene products and inactivators of cellular tumor suppressor proteins Proteins influencing viral virulence, host range, tissue tropism Virokines, which act on noninfected cells to modulate the progress of infection in the body as a whole |
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Which protein is critical for negative ssRNA virus replication?
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RNA dependent RNA polymerase
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How are genes regulated?
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gene regulators
transcription activator transcription regulator (p53 - without it, you have uncontrolled cell proliferation) transcription suppressor |
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What's an ORF?
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A section of a sequenced piece of DNA that begins with an initiation (methionine ATG) codon and ends with a stop codon (nonsense codon).
ORFs all have the potential to encode a protein or polypeptide, however many may not actually do so. |
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What are the promoter elements?
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The promoter contains specific DNA sequences that are recognized by proteins known as transcription factors. These factors bind to the promoter sequences, recruiting RNA polymerase, the enzyme that synthesizes the RNA from the coding region of the gene.
1. Core promoter - the minimal portion of the promoter required to properly initiate transcription. Transcription Start Site (TSS) Approximately -34 A binding site for RNA polymerase General transcription factor binding sites 2. Proximal promoter - the proximal sequence upstream of the gene that tends to contain primary regulatory elements. Approximately -250 Specific transcription factor binding sites |
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What happens during the assembly step of viral replication?
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Assembly of all the components necessary for the formation of the mature virion at a particular site in the cell.
-During this process, the basic structure of the virus is formed. The site of assembly varies for different viruses: -Cytoplasm --Picornaviruses, Poxviruses, Reoviruses - Nucleus --Adenoviruses, Papovaviruses, Parvoviruses - In the nucleus. -Cell Membrane (inner surface) --Retroviruses |
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What happens during virion assembly? Where do different virions assemble?
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Assembly of all the components necessary for the formation of the mature virion at a particular site in the cell.
During this process, the basic structure of the virus is formed. The site of assembly varies for different viruses: Cytoplasm Picornaviruses, Poxviruses, Reoviruses Nucleus Adenoviruses, Papovaviruses, Parvoviruses - In the nucleus. Cell Membrane (inner surface) Retroviruses |
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What happens during the maturation step of virion life cycle?
Are assembly and maturation inseparable processes? |
The stage of the life-cycle at which the virus becomes infectious.
Structural changes in the particle: -often resulting from specific cleavage of capsid proteins to form the mature products, -which frequently leads to a conformational change in the capsid, or the condensation of nucleoproteins with the genome. For some viruses, assembly and maturation are inseparable, whereas for others, maturation may occur after the virus particle has left the cell. |
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How do non-enveloped viruses exit from the host cell?
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For Non-enveloped viruses (lytic viruses), release is a simple process - the cell breaks open and releases the virus.
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How do enveloped viruses exit from the host cell?
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Enveloped viruses acquire the lipid membrane as the virus buds out through the cell membrane.
Virion envelope proteins are picked up during this process as the virus is extruded. |
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Does budding in virion exit kill the host cell?
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Budding may or may not kill the cell, but is controlled by the virus -cell
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What do the antiviral drugs amantadine and rimantadine inhibit?
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Inhibit one of the matrix proteins needed to get viral RNA into the cytosol
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What do the antiviral drugs zanamivir and oseltamivir inhibit?
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Block the neuraminidase and thus inhibit the release and spread of viruses
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During virion attachment and entry, what is the eclipse period?
How does the virus get released? (linearly?) |
Eclipse period (latent period): Interval between virus attachment/entry and appearance of the first progeny virions
Virus release: log phase of virion production |
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What are the steps of virus replication?
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Attachment and Entry
Genome replication -Processing of pre-mRNA -Translation -Intracellular Transport Assembly Exit/Maturation Virus growth cycle |
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What does MOI stand for? What is it determined by?
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The MOI is determined by simply dividing the number of viral particle added to the cells (PFU/ml) by the number of cells added (cells/ml).
MOI = No. viral particles/No.cells |
