Flashcards in Viruses & Prions (BE #4) Deck (71):
Describe the general structure of a virus.
nucleic acid surrounded by a protein capsid. Virus may be naked or enveloped.
What is a complete viral particle (nucleic acid + capsid + envelope if present) called?
Why are viruses considered obligate intracellular parasites?
They can only reproduce/replicate inside a host cell.
Why are viruses considered living?
They evolve by natural selection & they direct their own reproduction.
Why aren't viruses considered living?
1. They have no cell structure (no cytoplasm or plasma membrane)
2. Only have RNA or DNA
3. Lack a metabolism of their own
4. Do not contain all 4 groups of organic molecules (lack carbs & lipids)
5. Can only replicate within a host cell.
Describe the different variations on the viral nucleic acid.
1. will have RNA or DNA
2. Can be single stranded (SS) or double stranded (DS). Variations include:
Describe the 3 shapes of capsids.
1. polyhedral - triangles that fit together like a dome
2. helical - capsomes fit together as a spiral or helix to form a rod-shaped structure
3. Complex - combination viruses w/a polyhedral head & a helical portion (tail).
Explain how a virus acquires an envelope.
Part of the host cell's membrane pinches off when the virus leaves the cell.
Where are glycoprotein spikes found?
Why are they important?
They are found in the viral envelope. Viral glycolprotein spikes are coded for on the viral nucleic acid and are inserted into the host cell's plasma membrane prior to budding.
Spikes will only bind to certain receptors not he host cell surface & are essential for host specificity & viral infectivity. They can be thought of as "docking" stations.
Viruses that lack envelopes are called _________.
How does the presence of an envelope increase a virus' disease causing capacity?
1. They can hide viruses from the host's immune system.
2. They help viruses infect new cells by fusing with the host's plasm membrane.
What determines host range/viral specificity?
Viral specificity is determined by whether or not a virus can attach to a cell or not. Attachment depends on presence of receptor sites on the surface of the host cell & on specific attachment structures on the viral capsid or envelope.
___________ are viruses that attack bacteria.
List the 6 major steps of the viral lytic cycle.
4. biosynthesis - viral components (nucleic acids & proteins for capsids) are synthesized by the host cell.
6. release - hundreds of intact visions exit host cell (2 different ways - lysis or budding)
How do enveloped animal virions penetrate the host cell? (2 ways)
1. membrane fusion
2. receptor mediated endocytosis
How do most naked animal virions penetrate the host cell?
only the nucleic acid enters; the capsid stays on the outside.
How do bacteriophages penetrate the host cell?
The naked virus inserts its tail pin through the thick bacterial cell envelope& injects its nucleic acid into the cell. Capsid stays on outside.
What are the 2 ways virions are released from a host cell?
1. Burst/Lyses - if virus is naked, the protein lysozyme dissolves the plasma membrane (cytocidal).
2. Budding - if virus has an envelope, it pushes out the cell membrane, forming a bud that encloses the virus. The bud then pinches off behind. Cell is not lysed (cytopathic)
Naked viruses are released from the host cell by ______________.
bursting / lysis
Enveloped viruses are released from the host cell by __________.
Viruses that kill the host cell by lysis are called ____________.
Viruses that damage the host cell by budding are called ___________.
How do naked viruses cause their host cell to lyse?
The host cell produces the enzyme, lyzosome, which dissolves the plasma membrane.
Viral DNA that has become integrated into the host bacterial cell's chromosome is called a __________.
Viral DNA that has become integrated in an animal cells' chromosomes is called a __________.
What can trigger lysogenic viruses to go into the lytic cycle?
- temperature change
Examples of latent (lysogenic) animal viruses include:
1. herpes simplex 1 (fever blister)
2. varicella zoster (chicken pox / shingles)
3. HIV (AIDS)
4. HPV (warts & cervical cancer)
How does the bacteria Corynebacterium diphtheria cause disease?
The toxin produced by the bacteria is coded for on its prophage (integrated bacteriophage). So, the bacteria can only cause disease if it is infected by a specific virus.
What is a syncytium?
A multinucleate cell formed by the fusion of the plasma membranes of adjacent cells.
Only (naked or enveloped) viruses can form syncytia.
How does viral infection lead to syncytia formation?
The viral fusion protein that allows enveloped viruses to enter a host cell by membrane fusion causes the plasma membrane of adjacent cells to fuse.
How is syncytia formation an advantage for viruses?
Viruses can spread without having to diffuse through extracellular environment - this facilitates rapid viral dissemination & makes it difficult to attack them with antibodies.
Provide 3 examples of viruses that form syncytia.
1. Human Immunodificiency Virus (HIV)
3. Respiratory Syncytial Virus (RSV)
Viral family names end in __________.
How are viral species named?
Common English names
Give 3 examples of viral species.
4. Human Immunodeficiency Virus
Is the viral classification system natural or artificial?
What is the dilemma of growing viruses in the lab?
Cultivating viruses int he lab requires living cells & viruses are very specific for the cells they infect.
What is the disadvantage of growing animal viruses in the chicken embryos?
How was this solved?
viruses are very specific for the cells they infect. Not all viruses would infect chicken embryo cells.
In the 50's cell culture & tissue culture methods were developed from cancer cells.
Continuous cell lines are derived from what kind of tissue?
Cells keep dividing out of control, supplying an endless supply of cells for use in research.
One of the most famous continuous cell line is the __________.
HeLa cell line
How do physicians diagnose most viral illnesses?
Culturing viruses takes too long. Antibodies usually don't show up until patient has recovered.
Collections of viral components, such as capsids and nucleic acids, inside a cell are called _________. Rabies virus produce these structures specifically called _____________ in infected nerve cells.
What cytopathic effect does measles virus and RSV have on host cells?
Cause neighboring cells to fuse, creating giant, multinucleate cells (syncytia).
What cytopathic effect does Epstein Barrr virus have on lymphocytes?
Infects lymphocytes making them look huge & abnormal under the microscope.
Most animal viruses are ______ viruses (RNA or DNA).
Why do these viruses have a higher mutation rate?
B/c of the error rate of the enzymes involved in RNA replication.
How do retroviruses cause cancer?
What is an oncogene?
Inserting a normal provirus into a host chromosome near a normal gene might alter its expression & convert it to an oncogene
An oncogene is a gene that has the potential to cause cancer.
A _________________ is a drug or other agent that induces birth defects during embryonic development (it's able to cross the placenta).
Why are the Retroviruses referred to as the “backward viruses?”
In the process of transcription, our cells make RNA from our DNA. The retroviruses are RNA viruses, so must first make DNA from their RNA before they can be replicated. Since their process is opposite of ours, we call them “backwards.”
48. Give an example of a Retrovirus.
Human Immunodeficiency Virus - causes AIDS
Why must a Retrovirus undergo reverse transcription prior to becoming a provirus?
Retroviruses are RNA viruses and RNA cannot integrate with the host cell’s DNA; only viral DNA can integrate with the host cell’s DNA.
Explain the process of reverse transcription in Retroviruses.
This virus uses the enzyme reverse transcriptase to make DNA from its RNA. This DNA can then be integrated into the host cell's chromosome. The proviral DNA can now be transcribed into mRNA and translated into viral proteins to assemble new viruses for release.
What special enzyme must Retroviral capsids contain in order for replication to occur?
What is the action of AZT?
Blocks the action of reverse transcriptase enzyme (no DNA can be made from their RNA,) so the viral life cycle is interrupted.
Explain how antigenic shift produces new strains of influenza viruses.
can occur when 2 different flu strains infect the same cell;
it is likely that the RNA molecules of the 2 infecting virions recombine in various ways among the new virions, producing a virus that is significantly different from either of the original infecting strains.
Describe a tumor.
uncontrolled growth of tissue (cells are dividing out of control)
Tumors can be ___________ (non-life threatening) or ___________ (life threatening – they can metastasize to other tissues).
56. Most human cancers arise from ____________ or cellular damage caused by environmental factors such as ________________.
chemicals (nicotine, pesticides), UV, x-rays, diet
What do we call the series of blood tests used to detect antibodies to these viruses that can cross the placenta & harm the fetus?
What does TORCH stand for?
T - Toxoplasmosis
O - Other infections
R - Rubella
C - Cytomegalovirus
H - Herpes Simplex Virus
What diseases does “Other” refer to?
Hep B, Syphillis, Varicella Zoster (chicken pox), Parvovirus B19 (5th's disease)
What is a prion?
How do prions cause disease?
Prions cause normal proteins to mutate. The mutated proteins are taken up by the cell and lead to cell death. Cell death causes “holes” to appear in nervous tissue.
ID the animals affected by each of these prion diseases:
4. Wasting Elk disease
5. Mad Cow
4. elk & mule deer
What does CJD stand for?
What does BSE stand for?
Bovine Spongiform Encephalopathy
What is the theory for what caused the BSE epidemic in the UK?
BSE possibly originated as a result of feeding cattle meat-and-bone meal that contained scrapie-infected sheep products. There is strong evidence and general agreement that the outbreak was then amplified and spread throughout the United Kingdom cattle industry by feeding rendered, prion-infected, bovine meat-and-bone meal to young calves.
What are 2 forms of CJD? Which one is related to BSE?
1. Classic CJ - Not related to BSE
2. Variant CJD - Related to BSE
What causes classic CJD?
spontaneous transformation of normal prion proteins into abnormal proteins. A small percentage of patients (5-15%) may develop classic CJD b/c of inherited mutations of the prion protein gene.
How is vCJD transmitted?
Ingestion of contaminated meat;
improperly sterilized instruments
human growth hormone injections