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70 Cards in this Set
- Front
- Back
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T/F: Most viruses are little more than genes packaged in protein coats
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True
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T/F: Viruses occupy a "shady" area of life between life-forms and chemicals
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True
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T/F: Viruses are used as agents of gene transfer in gene therapy
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True
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How did researchers come to find out that viruses are much different than bacteria while studying them?
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Because bacteria could not be cultivated on nutrient media in test tubes or petri dishes; today we know this didn't work because a certain virus can ONLY live with its respective species of host cells
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T/F: Some of the smallest viruses are 20nm in diameter, smaller than a ribosome
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True
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Describe the basic possibilities for a virus's structure
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All viruses are nucleus acid surrounded in a protein coat, and some have a membranous envelope
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What is unique about the physical genomes of viruses? [2]
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It can consist of single or double stranded RNA or DNA, and the nucleic acids usually are in linear or circular molecular shapes
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What is the protein shell enclosing the viral genome called?
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A capsid (may be rod-shaped, polyhedral, etc.)
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Capsids are built from a large number of protein subunits called...
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Capsomeres (there are usually many of these in a capsid but only a very few TYPE of capsomere proteins)
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Rod shaped viruses are commonly called...
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Helical viruses
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Why are rod-shaped viruses like the tobacco mosaic virus called helical viruses?
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Because the capsomeres are arranged like a helix around the viral genome
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What is an adenovirus (that affects an animals respiratory tract) called and why?
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Icosahedral viruses because they are often arranged like a prism with 20 sides
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The membranous envelope that surrounds the capsids in many viruses is called a...
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Viral envelope
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What do viral envelopes contain and where are these things obtained?
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They often contain host cell phosopholipids and membrane proteins (as all membranes do) which are both obtained from the membranes of the host cell, and often have other proteins as well as glycoproteins of viral origin
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What are the two names for the often complex viruses that infect bacteria?
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Bacteriophages or simply "phages"
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What is the general stucture of a T2 or any T-even bacteriophage?
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An icosahedral head containing DNA with a tail sheath and little tail fiber "legs" that help it attach to the bacteria.
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Because viruses cannot survive on their own, lack the enzymes and equipment for making proteins, and cannot survive without a host, they are called...
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Obligate intracellular parasites
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Discuss the host range of viruses.
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Each virus has a specific range of hosts it can affect, depending on the receptor proteins of the host and its own surface proteins. Some can affect many animals, some can only affect certain tissues of one animal.
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Besides the injection of DNA like the t-even bacteriophage viruses, what are the two main ways a virus can enter the cell?
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Either through endocytosis or the fusion of the viral envelope with the plasma membrane
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Although viruses use all the organelles of the cell to create their proteins, how do DNA viruses get their DNA nucleic acid when forming new viruses?
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The DNA viruses use DNA poly II already present in the cell to replicate the injected DNA and to place it into a newly forming virus
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Although viruses use all the organelles of the cell to create their proteins, how do RNA viruses get the RNA nucleic acid copy they need to form new RNA viruses?
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The injected RNA usually codes for a protein (polymerase) that can copy the RNA itself, creating copies for the new RNA viruses being formed
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T/F: After either the RNA or DNA viruses have their genomes replicated and their proteins created, they spontaneously assemble into viruses with their nucleic acids surrounded by capsids
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True, hallelujah
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Some double-stranded DNA viruses can reproduce by two mechanisms, which are...
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The lytic and lysogenic cycles
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What is a lytic cycle?
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The cycle by which new viruses ultimately explode and destroy the bacterial cell in which they were created
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A bacteriophage virus that only reproduces by the lytic cycle is a...
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Virulent phage
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Most of the lytic cycle of a T-4 phage is as expected, except at step #2. What happens here?
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One of the first genes of the phage DNA that is transcribed/translated creates an enzyme that degrade's the bacterial cell's DNA and no longer allows for its use.
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What are the two main reasons bacteriophages haven't eliminated all bacteria?
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Bc natural selection gives rise to mutated bacteria with new receptors that are no longer recognized by viruses for attachment, and bc when the viral DNA is inserted into the bacterium the DNA is often seen as foreign and so is chopped apart
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What are the enzymes called that cut up the injected viral genome by recognizing it as foreign?
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Restriction enzymes (restriction enzymes don't cut up the bacteria's own DNA bc the bacterial DNA is methylated so that it can be recognized)
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T/F: Just as evolution by natural selection favors mutated bacteria with altered receptor proteins, it also favors viruses that can bind to the altered receptors or are resistant to restriction enzymes.
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True; so the phage-bacteria relationship is in a constant evolutionary struggle
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What is the state called in which a phage exists with its bacteria without destroying it?
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Lysogeny
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The cycle that allows replication of the phage genome without destroying the host is the...
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Lysogenic cycle
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Phages capable of using but lytic and lysogenic types of reproduction are called...
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Temperate phages
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How is a lambda-phage (symbolized λ) different from a T-4 phage?
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It only has one, short tail fiber
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At what step in the phage pathway is the lytic or lysogenic cycle determined?
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Once the phage DNA forms a circle; it can then go lytic or lysogenic
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If the viral cycle goes lysogenic, then viral proteins cut the circular bacterial DNA and the (now) circular phage DNA an incorporate them into one circle. What is the phage DNA called now that it is incorporated into the bacterial DNA?
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A prophage
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Now describe the overall lysogenic cycle after the formation and incorporation of a prophage.
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Once the prophage (DNA) is in the single, circular bacterial chromosome, it silently turns itself off and replicates, thus being in many more generations of bacteria. Environmental factors can cause the prophage to exit the bacterial chromosome and initiate the lytic phase.
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T/F: Although during lysogeny the off-protein is formed from the prophage turning off most of its transcription, a few prophage genes can be expressed which may alter the bacteria's phenotype, often making it deadly.
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True; e.g., e. coli is in our intestines but e. coli in raw meat that can kill people is only different in that it has prophage DNA being partially expressed which releases toxins
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T/F: The nature of a viral genome is often the basis for the classification of the virus
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True
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What is true about the structure of many animal viruses?
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They have envelopes and an RNA genome, unlike the phages.
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What two things do the viral RNA injected into an animal cell code for and where do these things go?
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Viral RNA is turned into mRNA and codes for capsid proteins made in free ribosomes, and for glycoproteins which are made by bound-ribosomes and sent from the Golgi app to the cell membrane where they attach and wait to by carried out by capsid-surrounded RNA genomes waiting to obtain their viral envelope from the animal cell membrane. The copied, new virus now leaves the cell complete and ready to infect others.
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T/F: Some viruses have envelopes that are not derived from plasma membrane
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True
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What is unique about herpesviruses?
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They are not coated in viral envelopes derived from plasma membranes but rather in envelopes from nuclear membranes and then membranes from the Golgi apparatus.
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Type IV ssRNA serves directly as mRNA for synthesis of proteins. How is type V RNA different?
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It serves as a template for mRNA creation; this COPY of the initial viral RNA can be mRNA or can serve as a template for replication and creation of more identical RNA strands.
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What does reverse transcriptase do?
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It takes a single RNA strand and turns it into a normal DNA strand
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An enveloped virus with two identical molecules of single-stranded RNA and two molecules of reverse transcriptase are called...
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Retroviruses (e.g., AIDS)
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What are the 2 jobs of reverse transcriptase?
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To replicate the ssRNA from the virus into a complementary ssDNA, and then to make another ssDNA complementary to the first one. These then fuse together to form dsDNA from the initial ssRNA.
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Once the new dsDNA from the initial ssRNA is formed and incorporated into the animal cell genome, it is called...
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A provirus (never ever leaves the genome now)
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What happens after the dsDNA from the original viral RNA is now a provirus in the cell genome?
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It is transcribed into mRNA to make capsid proteins and can also just be replicated by the host cell's RNA poly III for incorporation into the new retrovirus
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T/F: It seems likely that viruses developed AFTER cells did, because they cannot survive without a cell.
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True
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Most people believe that viruses may have evolved from plasmids and transpoons. What are these things?
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Plasmids are small, circular DNA molecules in unicellular organisms that exist apart from the genome and can replicate on their own and be transferred from cell to cell. Transpoons are DNA segments that can move from one location to another within a cell's genome.
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What do viruses, plasmids, and transpoons all have in common?
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They are mobile genetic elements
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What did the complexity of the mimivirus do to the idea of viral evolution?
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It made scientists think that viruses possibly evolved before bacteria or just cells in general
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T/F: Viruses may cause damage by releasing hydrolytic enzymes from the lysosomes of cells, they may produce troxins leading to disease, or they may have toxic molecular components themselves, such as envelope proteins.
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True
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What are the usual symtoms associated with the common cold actually caused by?
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They body trying to heal itself
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The major medical tool for preventing viral infections which is a harmless variant or derivative of a pathogen that stimulates the immune system to mount defenses against a harmful pathogen is called a...
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Vaccine
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T/F: We are sometimes able to prevent viral infections but there is little we can do once someone is infected with one, bc the antibioitics we take only inhibit bacterial enzymes. Most antiviral drugs resemble nucleosides and as a result interfere with viral nucleic acid synthesis.
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True
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HIV, Ebola, and West Nile Virus are all examples of...
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Emerging viruses
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Why is mutation of existing viruses one of the main reasons for viral outbreaks?
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Bc RNA viruses often have so much error in replication bc there it no proofreading for mistakes like there is in eukaryotes. [Flu epidemics are caused by this each year]
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Another reason for viral emergence is the dissemination of a virus from a small group of people to many others all over the world by behavior, such as...
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HIV
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3/4 of new human diseases originate from...
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Other animals
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What are other animals called that harbor viruses unharmful to them but deadly to us once ingested?
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They are called natural resevoirs [e.g., bats are eaten in China and are though to be the natural resevoir of the SARS virus]
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What is a pandemic? What was the first major one of the 20th century and where is it thought to originate?
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A global epidemic; the Spanish flu pandemic of the 19-teens, thought to come from birds
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What is the deadliest situation of viruses?
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If they get together and join DNA, becoming a highly-pathogenic and speadable "recombinant" virus
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Most plant viruses have a/an _ genome.
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RNA
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What are the two types of spreading of plant viruses and describe them.
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Horizontal transmission (when a human or herbivore or anything else gives a plant a virus, breaking its epidermis from the outside), or vertical transmission (when a plant gets the virus from its parent via asexual reprod. or sexual reprod. through an infected seed)
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How do viruses travel from cell to cell in plants?
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They create proteins from their nucleic acids that englarge plant plamodesmata and travel through these
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Viroids are...
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Small, circular strands of RNA that cause disease (like stunted growth, etc.) in plants
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What are prions and how are they spread?
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Infectious proteins in animals that usually are spread by food, or (as one case in South America occurred) through cannibalism
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What are the two most dangerous characteristics of prions?
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They have an incubation period of at least 10 years, and they are virtually indestructible even with large amounts of heat
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How is it generally thought that prions replicate if they are just small proteins?
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It is thought that they are just misfolded forms of regular proteins, which bind to the regular protein and make it match prion form. Then, all these irregular prions aggregate and cause cell function to halt.
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