Viruses
What is going on when Early and Late gene products are produced during DNA viral replication?
Early products are enzymes and DNA binding proteins that initiates the transition to transcription to produce late gene production. Late products include viral structural and other proteins that are required to package the virus.
What are some of the advantages/disadvantages of viral isolation, ELISA, PCR, serology?
Some disadvantages of these laboratory test are that they do not always have conclusive results. For example, shedding of the virus may or not always be occurring. That or another virus could be present that is not the one that is being sought after.
After nucleic acids, what is the main way of classifying viruses?
Structure and morphology, along with how it replicates, spreads, and causes disease.
What is tricky about using antiviral drugs to block RNA synthesis?
You don't want to block self-cells RNA synthesis. You have to target the synthesis of viral RNA, while not affecting self RNA synthesis. Creating molecules that are specific (and highly specific) to only the enzymes used in RNA synthesis is very important. Without transcription of self RNA, the organism would die.
What is a lytic infection and what are the ways that viruses cause cell death?
A lytic infection is when the infection kills the cells it targets. One way viruses cause cell death is by damaging the cell and then impeding repair by inhibiting synthesis of macromolecules or producing degradative enzymes or toxic proteins. Replication of the virus can alter the structure and function of the cell or disrupt lysosomes, causing cell death. Viruses may induce apoptosis (casacade of events leads to cellular death) which leads to cellular death. Cell death can also occur with syncytia (multinucleated giant cells, fusion) because they are susceptible to lysis.
What is a viral envelope?
A membrane covering the virus composed of lipids, proteins, and glycoproteins. It is only maintained in aqueous solutions and is readily disrupted by drying, acidic conditions, detergents and solvents such as ether, which results in inactivation of the virus. They are generally transmitted in fluids such as respiratory droplets, blood, and tissues. Most enveloped viruses are round or pleomorphic.
What is the function of a viral envelope?
A membrane covering the virus composed of lipids, proteins, and glycoproteins. It is only maintained in aqueous solutions and is readily disrupted by drying, acidic conditions, detergents and solvents such as ether, which results in inactivation of the virus. They are generally transmitted in fluids such as respiratory droplets, blood, and tissues. Most enveloped viruses are round or pleomorphic.
What is a viral capsid?
A protein coat that has a rigid structure that is able to withstand harsh environmental conditions. They are resistant to drying, acid, and detergents including bile of the enteric tract.
What is a virion?
A virus particle that consist of nucleic acid genome that is packaged into a protein coat or membrane.
How does assembly take place?
After the necessary pieces are synthesized in a sufficient quantity, the virion is assembled. Assembly of DNA viruses typically occurs in the nucleus, requiring the transport of virion proteins into the nucleus, and assembly of RNA viruses occurs in the cytoplasm. The exact mechanisms of assembly depend on the type of virus. Capsid viruses may assemble as empty structures, which are then filled with the viral genome, or the capsid may assemble around the genome. For enveloped viruses, viral glycoproteins are transported to cellular membranes by vesicle transport, as viral nucleocapsid is associated with the glycoprotein containing regions of the membrane, the virus is enveloped.
What is budding?
Budding is the process in which viral nucleocapsid gains an envelope from a host cell membrane. As the membrane surrounds the nucleocapsid a bud is formed, as the virus is completely enveloped, it buds off of the membrane.
What is CPE and what is the difference between syncytia and plaque?
CPE stands for cytopathologic effects which refers to morphological changes caused by a virus invading a host's cell. CPE can also include cell lysis, vacuolation,syncytia, and inclusion bodies. Syncytia is a type of cytopathologic effect where viral fusion of cells creates giant multinucleated cells. As opposed to plaque which is where a virus kills surrounding cells. The difference between the two is how you observe viruses. Syncytia would require use of a microscope and plaque would require you to observe a cell culture.
How is uncoating blocked?
Coating is blocked by attaching to the part of the capsid that binds to the host receptor and effectively prevents the capsid from disassembling and releasing the viral genomic material into the cytoplasm of the host cell. For viruses that enter the host via endocytic vesicles, uncoating can be initiated by the acidic environment of these vesicles. Weak organic bases are utilized as antiviral agents because they can neutralize the pH of these vesicles and prevent the initiation of uncoating.
What types of nucleic acids do viruses have?
DNA and RNA
What are the fundamental differences between DNA virus and RNA virus replication?
DNA viruses use the host cell polymerases and enzymes to create viral mRNA, and viral replication is similar to that of cellular DNA. Most DNA viruses reside in and are transcribed in the nucleus. Smaller DNA viruses rely only on host polymerases and enzymes for replication; therefore, they are dependent on the host cell and are limited by the availability of replication tools. Due to this, some small DNA viruses only replicate in growing cells. In RNA viruses, the host cell does not have any way to translate and transcribe RNA, therefore the RNA virus must code for RNA-dependent RNA polymerases. Most RNA viruses reside in and are transcribed in the cytoplasm. Rna virsuses must encode enzymes that are required for transcriptions and replications because it doesn't (cell) have means to do so.
What are the five ways to identify a viral infection?
Five ways to identify a viral infection can be done by conducting viral laboratory studies which described the cytopathologic effects on cells which were induced by the virus, by detecting viral particles, by isolating and growing the virus, by detecting and analysing viral components (antigens, proteins, genomes, and enzymes), and by looking over the patient's immune response to the virus.
What are the 4 potential outcomes of viral infection?
Four potential outcomes of a viral infection are failed infection, cell death, persistent infection (replicating with no cell death), and latent-recurrent infection.
How does Interferon work to stop viruses?
Interferons boost the immune system and its response to the virus. When a cell becomes infected, it releases interferons (IFN-alpha I believe, though I don't remember), which serves as almost a warning to nearby cells that they are infected by a virus. The nearby cells can act more "cautiously" promoting an anti-viral proteins that helps prevent the replication of viruses inside of cells. They can also help bring an immune response to the sight, almost like a red flag. The immune response can identify the virus and specific proteins on the cell, bring them to a lymph node to produce antibodies to the virions and promote macrophage digestion of the infected cell, completely digesting the host cell and all viral compounds contained.
What is an obligate intracellular parasite?
It means that they depend on the biochemical machinery of the host cell for replication, they cannot replicate outside of a host cell by themselves.
What is the function of a viral capsid?
It is the package, protection and delivery vehicle during transmission of the virus from one host to another and for spread within the host to the target cell. It is made up from individual proteins together to form a larger unit. Individual proteins subunitsprotomerscapsomeresprocapsidcapsid.
How does PCR work and how does it detect viruses?
Polymerase chain reaction and reverse polymerase chain reaction allows you to amplify DNA. Having the DNA of the virus amplified allows for labeling with a probe to identity the virus.
What are some of the steps or targets that antiviral drugs target?
Targets include the attachment of the virus to the host's membrane, targeting the uncoating step, or targeting the release of new virions. To block attachment of a virion to a host it is necessary to disrupt receptors on each membrane (virion and host cell). So there are two targets (mainly). You can have antibodies that bind to receptors on the host cell that are called neutralizing antibodies. With the host's cell receptors essentially "blocked" from a virion, the virion is unable to infect a host, and will eventually die being that it is an obligate parasite. You can also construct antibodies that attach directly to the virus, mimicking a host cell's receptors. This is another way to prevent the interaction between a virion and a host cell. If a virus does interact with a host cell's receptors and enters the cell it must release its genomic material to have an effect. The virus must "uncoat" itself and its genetic material to begin transcription and translation. Host pH and enzymes can contribute to uncoating and also the virus may self-contain the enzymes required for uncoating. This can be done with drugs that block ion channel proteins on the capsid or other capsid proteins important to the uncoating process. The last mechanism is containing newly formed virions that are still contained in the cell. Neuraminidase is an enzyme on the capsid of some virions and results in the release of the virions from the cell. Targeting neuraminidase (either competitive/noncompetitive/uncompetitive inhibition) or its receptor (as described earlier with cell surface receptors or virion's receptors) can lead to inhibited release of virions.
What is occurring with viral mRNA synthesis?
The first stage in the viral replication cycle is expression of the viral genes. Transcription of these genes occurs using cellular transcription factors. These early RNAs are processed (capped, polyadenylated and spliced) in the nucleus, and are then transported to the cytoplasm where they are translated, giving rise to the early proteins. Viral mRNA synthesis is when the genome must direct the synthesis of viral mRNA and protein and make copies of itself. If the genome does not have functional mRNA, it won't be able to bind to ribosomes and make proteins
What happens during each step?
The first step in viral replication is attachment. In this phase, the surface proteins of the virus attach with receptors of the host cell. The second step is penetration. Enveloped viruses penetrate cells through fusion of the viral envelope with the host cell membrane. Non-enveloped viruses penetrate cells by translocation of the virion across the host cell membrane or receptor mediated endocytosis of the virion in clathrin coated pits with accumulation of viruses in cytoplasmic vesicles. The third step is uncoating. This process makes the nucleic acid available for transcription to permit multiplication of the virus. The fourth step is transcription and translation. The virus must use the host cell machinery to replicate and functional and structural proteins. The last step of viral replication is assembly and release. The process of virion assembly involves bringing together newly formed viral nucleic acid and the structural proteins to form the nucleocapsid of the virus. There are basically three strategies that viruses employ: 1. Nonenveloped viruses exhibit full maturation in the cytoplasm (e.g., picornaviruses) or the nucleus (e.g., adenoviruses) with disintegration of the cell and release of virions. 2. For enveloped viruses, including the (-) strand RNA viruses, the (+) strand togaviruses and the retroviruses, final maturation of the virion takes place as the virion exits the cell. Viral proteins are inserted into the host cell membrane. Nucleocapsids bind to the regions of the host cell membranes with these inserted proteins and bud into the extracellular space. Further cleavage and maturation of proteins may occur after viral 2 extrusion to impart full infectivity on the virion. Viruses in this group differ in their degree of cytolytic activity. 3. Herpesviruses, which are enveloped viruses, assemble their nucleocapsids in the nuclei of infected cells and mature at the inner lamella of the nuclear membrane. Virions accumulate in this region, in the endoplasmic reticulum and in vesicles protected from the cytoplasm. Release of virions from the cell surface is associated with cytolysis.
What are the main paths of entry into the host body?
The main paths of entry into the host body are through the skin (cuts, bites, injections) or from mucoepithelial membranes such as eyes, respiratory tract, genitalia, mouth, and GI tract.
What are the basic steps in viral replication?
The major steps in viral replication are the same for all virus types: attachment, penetration, uncoating, transcription and translation, and assembly and release.
How else (besides extracellular release) can viruses spread infection?
The virus can be transmitted through cell-to-cell bridges, through cell to cell fusion, or through cellular replication to daughter cells.
What is the principle difference between viruses and other cellular organisms?
They are vastly smaller. Their genome that codes for DNA which leads them to take over another cell and reproduce themselves. They cannot make energy, or substrates and cant make their own proteins
What are capsids and envelopes composed of and why does it matter?
They consist of either DNA or RNA. The DNA can be single or double stranded, linear or circular. The RNA can be positive or negative sense, double stranded positive or negative or ambisense. It can also consist of segmented pieces each encoding one or more genes. They are important because they maintain and transmit the genetic information of the virus and also trigger the conversion to the final form.
What is a VAP and why is it important?
VAP (Viral Attachment protein) are what bind to structures on target cells. VAPs that also bind to erythrocytes are termed hemaglutinins.
How are viruses released from the cell?
Viruses can be released when a cell is lysed, by exocytosis, or by budding from the plasma membrane.
What is uncoating and where does it occur for a DNA virus?
With some viruses, the genome is completely released from the capsid during or after penetration (the mechanism by which a virus enters the host cell). This is known as "uncoating". The genome of DNA viruses are commonly released in the nucleus of the host whereas RNA viruses have a genome that remains in the cytoplasm.
How are viruses internalized into a host cell?
endocytosis viropexis fusion of enveloped virus