Bio 225 Chapter 13 Objectives
Define capsid.
protein coat
Define capsomere.
subunits of the capsid
What is a tumor?
A tumor, also known as a neoplasm, is an abnormal mass of tissue which may be solid or fluid-filled. A tumor does not mean cancer - tumors can be benign (not cancerous), pre-malignant (pre-cancerous), or malignant (cancerous).
What are the steps in the multiplication of animal viruses? Give the proper sequence and describe what occurs in each step.
1. Attachment: Attachment sites are plasma membrane proteins and glycoproteins. 2. Entry: Capsid enters the endocytosis or fusion. 3. Un-coating: Enzymatic removal of capsid proteins. 4. Biosynthesis: In nucleus(DNA viruses) or cytoplasm (RNA viruses). 5. Chronic Infection: Latency: slow viral infections; cancer 6. Release: Enveloped viruses bud out; nonenveloped viruses rupture plasma membrane.
How are animal viruses cultured in the laboratory?
1. Live animal cultures have to be used for some animal viruses. Simian AIDS and feline AIDS provide models for studying human AIDS. 2. Embryonated eggs can serve as substitutes for some viruses. Can inoculate membrane that best supports specific virus (allantoic, amniotic, chorioallantoic, or yolk sac).
What are viral envelopes?
3. Envelope - the outer covering of some viruses.
What is a plaque?
After replication the virus lyses the bacteria, forming plaques, or clear zones. Each plaque is assumed to come from a single viral particle.
Give some examples of oncogenic viruses.
Found among: Adenoviruses Herpesviruses EBV Burkitt's lymphoma Nasopharyngeal carcinoma Herpes simplex Association with cervical cancer Poxviruses Papovaviruses Human papilloma viruses (especially HPV-16) - cervical cancer Hepadnaviruses HBV - hepatocellular carcinoma
What is the difference between primary, diploid and continuous cell lines?
Cell culture is a lot cheaper and easier to work with (contamination can be a problem however). Primary cell lines have a short lifespan in culture - a few generations before reaching senescence. Diploid cell lines are derived from embryos and can grow for up to 100 population doublings before senescence. Continuous cell lines are derived from transformed cells and grow indefinitely in culture.
What are the three types of viruses based on the types of organisms they infect?
Classification: Animal virus Plant virus Bacterial virus (bacteriophage
Viral growth can cause cytopathic effects in the cell culture.
Cytopathic effects can appear early or late in the course of the viral infection. Cytopathic effects may be cytocidal (cell death) or non-cytocidal. Non-cytocidal effects include acidophilic or basophilic inclusion bodies in the nucleus, cytoplasm, or both; cell fusion, and transformation. Cytopathic effects can be so characteristic of individual viruses that they can often be used to identify viruses.
Define virus.
Definition: Obligate intracellular parasite composed of: Nucleic acid - either DNA or RNA Protein coat
What is Metastasis?
Development of secondary tumors distant from the site of the original tumor, characteristic of malignant tumors
What kind of diseases do prions cause?
Diseases: Scrapie (sheep) Transmissible mink encephalopathy Bovine spongiform encephalitis (mad cow disease) Kuru - New Guinea, contracted by eating infected brain tissue (cannabilism was a mourning rite among members of this particular tribe between about 1920 and 1950) Creutzfeldt-Jakob disease (CJD) is very similar and has a heritable form and may be passed by contact (neurosurgery, corneal transplants, pituitary-derived GH preparations) Gerstmann-Straussler-Scheinker syndrome (GSS) similar, inherited
How are enveloped viruses released from host cells?
Enveloped viruses bud out
Differentiate between the lytic cycle and lysogeny.
Events of the lytic cycle: Attachment or adsorption Requires a receptor Penetration: T-evens release lysozyme to break down a portion of the cell wall. The tail sheath contracts and the tail core is driven through the hole in the wall to the plasma membrane. The viral genome is then injected into the bacterium. Biosynthesis: Viral DNA and proteins are synthesized. Host protein synthesis is stopped by degradation of host DNA, interference with transcription, or repression of translation. Maturation: During maturation or assembly phage DNA and capsids are assembled into complete viruses. Release: Release occurs when phage lysozyme breaks down the cell wall and newly synthesized phage particles are released. Lysogeny is a cycle in which the phage DNA recombines with the bacterial chromosome.
What are the five morphological types of viruses?
General Morphology Based on capsid architecture, although enveloped viruses end up being approximately spherical. 1. Helical, non-enveloped 2. Helical, enveloped 3. Polyhedral, non-enveloped 4. Polyhedral, enveloped Polyhedral means many sides (most are icosahedral - 20 triangular faces and 12 corners) 5. Complex viruses are, well, complex.
Identify the site of viral protein synthesis.
Host cell cytoplasm
What determines the host range of a virus?
Host range is determined by attachment sites (receptors). Anti-bacterial therapy - phage therapy Anti-tumor therapy - oncolytic viruses
List two kinds of viral spikes and describe their function.
Influenzavirus has two kinds of spikes, H (hemagglutinin) and N (neuraminidase). The H spike allows the virus to attach to host cells (and red blood cells), the N spike is an enzyme that allows the mature viral particles to escape from the host cell
What is the difference between latent and persistent viral infections?
Latent Viral Infections Many viruses, especially the human herpesviruses, can remain in host cells throughout life without causing disease. They may be reactivated by immunosuppression, however, and cause disease. Examples: Cold sores Shingles Persistent Viral Infections Persistant viral infections (formerly termed slow viral infections) are progressive over a long period of time and are usually fatal. Persistant viral infections are different from latent viral infections in that the detectable virus builds slowly over a long period of time rather than appearing suddenly. Examples: Subacute sclerosing panencephalitis (Measles virus) Progressive encephalitis (Rubella virus) Progressive multifocal leukoencephalopathy (Papovavirus) AIDS dementia comples (HIV) Persistant enterovirus infection (Echoviruses) Progressive pneumonia (retrovirus)
Describe viral multiplication in bacteriophages.
Multiplication of Bacteriophages The virus may cause lysis or lysogeny.
Describe what occurs in the biosynthesis of a virus with reverse transcriptase.
Multiplication of Retroviruses Retroviruses use reverse transcriptase (RNA-dependent DNA polymerase) to transcribe DNA from RNA. Both viral RNA strands are + strands (making the virus diploid, how about that?) which are transcribed by reverse transcriptase to make complementary DNA strands. The original viral RNA is degraded and the DNA copies integrate into the host cell's genome.
What is the difference between an enveloped and a naked virus?
Non-enveloped or naked viruses are protected by their capsid alone.
How are non-enveloped viruses released from host cells?
Non-enveloped viruses rupture plasma membrane.
What kind of nucleic acid do viruse have?
Nucleic acid Viral genomes are either DNA or RNA (not both). Nucleic acid may be single- or double-stranded Nucleic acid may be circular or linear or separate molecules. Nucleic acid:protein ranges from about 1% - 50%.
How are bacteriophages cultured in the laboratory?
Once viruses have replicated and been harvested the concentration of viral particles (virions) in the viral stock solution must be determined. One of the easiest ways to determine the concentration of a stock solution of bacteriophages is to use the plaque method. The plaque method: Virus, bacteria, and agar mixed, plated and incubated.
What is an oncogene?
Oncogenes - genes involved in tumor formation, first identified as part of viral genomes. It was later shown that the viral oncogenes were actually derived from animal cells.
What are the possible outcomes of lysogeny?
Outcomes of lysogeny Bacterium can't be reinfected by the same kind of phage. Host cell may exhibit new properties due to viral genes carried on the prophage Specialized transduction - host cell may gain new bacterial genes packaged with the phage
What are prions?
Prions are infectious proteins. Insoluble aggregates of protein with normal primary sequence but exhibit altered folding pattern. The normal protein (PrPc) is coded for by a gene on chromosome 20. The abnormal form (PrPSc) is found in disease states. Abnormally-folded proteins (PrPsc) cause normal proteins to assume the pathogenic conformation. The diseases are spongiform encephalopathies that cause large vacuoles to appear in the brain.
Explain the importance of reverse transcriptase.
Reverse transcriptase produces viral DNA that integrates into host genome as a provirus.
List the characteristics of viruses.
Single type of nucleic acid - DNA or RNA Protein coat, or capsid, some have envelopes Multiply inside of living cells using the host cell machinery Direct the synthesis of structures to transfer viral nucleic acid to other cells
What are viral spikes?
Some enveloped viruses have spikes, which are viral glycoproteins that project from the envelope
Where do viruses acquire Viral envelopes?
The envelope is derived from the host cell plasma membrane when the virus buds out. .
What is a prophage?
The incorporated viral DNA is now a prophage. The prophage genes are regulated by a repressor coded for by the prophage, the prophage is replicated each time the host DNA is replicated. Exposure to mutagens can lead to excision of the prophage and initiation of the lytic cycle.
What is the host range of virus?
The specific types of cells a virus can infect in its host species represent the host range of the virus. Usually species specific
What kind of information do you get from a plaque assay?
The titer (concentration of the stock solution) of the virus is given in plaque forming units.
What are cytopathic effects? Describe the cytopathic effects of viruses on host cells.
The visible or morphologic changes induced in a host cell by a virus that may result in host cell damage and/or death
What is the difference between a benign and a malignant tumor?
Tumor Types: Benign - tumors that generally don't spread, can be removed, and aren't life threatening Malignant - invasive, generally aggressive tumors that are life threatening
Oncogene and suppressor gene which is "activated" and which is "lost"?
Tumor-suppressor gene must be lost or inactivated in order for the Oncogenes to be activated (to function abnormally or without normal controls) by mutagenic chemicals, radiation, and viruses. Activation events may include mutation, transduction, translocation, and amplification. Oncogenic viruses are capable of producing tumors in animals. Oncogenic viruses integrate into host cell DNA and may cause transformation of host cells. Transformed cells lose contact inhibition, contain virus-specific antigens (tumor-specific transplantation antigen (TSTA)on the cell surface or T antigen in the nucleus), exhibit chromosomal abnormalities, and can produce tumors when injected into susceptible animals.
What are the major methods used for viral identification?
Viral Identification Serological methods Western blotting Cytopathic effects Diagnostic inclusion bodies are associated with rabies virus, measles virus, vaccinia virus, smallpox virus, herpesvirus, and adenoviruses. Molecular methods include PCR and RFLPs. PCR was used to identify the West Nile virus and the SARS-associated coronavirus
Define virion.
Virions are complete, fully developed viral particles composed of nucleic acid surrounded by a protein coat. Some viruses have an envelope composed of a phospholipid bilayer with viral glycoproteins.
What is a viroid?
Viroids are naked (lacking a protein coat) pieces of RNA that can cause some plant diseases. They are internally base paired, so they assume a folded conformation that protects them from enzymatic degradation. Viroids don't code for proteins and research indicates that they have similarities to introns, which suggests researchers may discover animal viroids in the future.
Describe the composition of a virus.
Virus particles consist of genetic material (DNA or RNA) enclosed by a protein coat, called a capsid
Where do viruses multiply?
Viruses do not contain enzymes for energy production or protein synthesis. For a virus to multiply, it must invade a host cell and direct the host's metabolic machinery to produce viral enzymes, viral proteins, and copies of its nucleic acid, using the host cell's ATP to power the reactions.
What is a tumor suppressor gene?
a suppressor gene that blocks unscheduled cell division
Define protomere.
capsomere subunits
