32) The diversity in _____________ in viruses reflects the diversity among viruses: a) organelles b) enzymes c) genetic material d) proteins e) cell membranes 33) The fact that viruses target specific tissues within the host they infect is called: a) Tissue Tropism b) Chemotaxsis c) Chemotropism d) Biotropism e) Biotaxsis 34) Bacteria that use reduced, performed organic molecules as their carbon source are labeled as: a) Organotroph b) Chemotroph c) Autotroph d) Heterotroph e) Lithotroph 35) The HIV virus is classified as: a) RNA virus b) Retrovirus c) Virusoid d) Filovirus e) b & c 36) Most animal viruses exhibit a shape called: a) icosahedral b) spherical c) helical dtetrahedral e) Complex binary 37) The protein coat that surrounds the genetic material of the virus is called: a) capsule b) capsid c) cell wall d) capsomer e) shell 38) The enzyme present in the HIV which must be injected with the genetic material is called: a) Reverse Replicase b) Reverse RNAase c) Reverse Transcriptase d) Reverse Polymerase e) Retro DNAase 39) Viroids are: a) RNA viruses b) Viral particle outside a cell c) special viruses that infect plants d) Satellite viruses e) a & c 40) Virions are: a) RNA viruses b) Viral particle outside a cell c) special viruses that infect plants d) Satellite viruses e) a & c 41) If a bacteria is labeled organotroph, this means it derives: a) its carbon source from organic material b) its carbon source from inorganic material c) its energy from breaking bonds from organic material d) its electrons from breaking bonds from organic material e) its electrons from breaking bonds from inorganic material 42) Plant or animal extracts are good examples of ___ gel: a) complex b) supportive c) defined d) nutritive e) a & c 43) The virusoid genome is: a) dsDNA Linear b) dsDNA Circular c) ssDNA Linear d) dsRNA Circular e) ssRNA Circular
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Viruses evolve but leave no fossil evidence that can be used to construct phylogenies. However, viral DNA, especially that of retroviruses, is commonly found in the host genome. By comparing sequences from the same virus integrated at different points in time, the evolutionary history of the virus can be constructed. The viral genomes are typically found incomplete, in segments, and interrupted by stop codons. In jawed vertebrates, retroviral sequences or sequences that have been derived from them are a significant fraction of the whole genome. A. Explain why retroviral DNA rather than the genomes of single-stranded or double-stranded DNA or singlestranded RNA viruses are found in host DNA. Exaptation occurs when gene expression provides a function that is independent of the selection pressures that have acted on the gene. For example, a pigment that provided selective advantage by reducing damage from solar radiation becomes an element of mating behavior. Feathers that evolved under selection to prevent heat loss become a means of flight. In a study of viral evolution within host genomes of primates, Katzuorakis and Gifford (PLOS Genetics, 2010) found that viral genomes within the host were surprisingly stable; with computer simulation, they estimated the probability of such constancy at 1 in 100,000. B. Explain in terms of selection how viral genetic information that no longer replicates the virus is maintained by the host. Distemper is an incurable disease of cats, dogs, and their sister lineages caused by a parvovirus. The virus exploits the host’s transferrin, a membrane-bound protein used for iron transport, to attach to the cell. The phylogeny of the Parvoviridae family has been constructed (J. Kaebler, PLOS Pathogens, 2012). That study revealed the evolution of both the virus and the host protein through selection to resist infection. About 54 million years ago when the lineage of cats (Feliformia) diverged from that of dogs (Caniformia), the parvovirus envelope diverged as well, conforming to changes in the host’s transferrin. In 1978, a worldwide disease in dogs due to a parvovirus suddenly appeared. C. Explain how this pandemic could have originated in the cat population entry process and discovered that the actin protein on the host cell’s surface that provided the viral receptor was modified by attachment. They then found a mutant virus that did not modify the cell surface protein. The dependence of the growth of plaque radius on time for the wild type and mutant are shown in the graph.
A virus that grows in bacteria (bacterial viruses are called bacteriophages) can replicate in one of two ways. In the prophage state, the viral DNA is inserted into the bacterial chromosome and is copied along with the bacterial genome each time the cell divides. In the lytic state, the viral DNA is released from the bacterial chromosome and replicates many times in the cell. This viral DNA then produces viral coat proteins that together with the replicated viral DNA form many new virus particles that burst out of the bacterial cell. These two forms of growth are controlled by two transcription regulators, the repressor (product of the $c I$ gene) and Cro, both of which are encoded by the virus. In the prophage state, $c I$ is expressed; in the lytic state, Cro is expressed. In addition to regulating the expression of other genes, cI represses the Cro gene, and Cro represses the $c I$ gene (Figure $Q 8-4$ ). When bacteria containing a phage in the prophage state are briefly irradiated with UV light, cI protein is degraded. A. What will happen next? B. Will the change in (A) be reversed when the UV light is switched off? C. What advantage might this response to UV light provide to the virus?
Influenza A virus is the most pathogenic of the human influenza viruses. Its envelope encloses a protein complex (vRNP) and eight, single-stranded, negative RNA (the complement of a positive RNA strand that can be transcribed by a ribosome) segments (vRNA). Each segment encodes one or two proteins that support viral replication. On the outer surface of the envelope are proteins that recognize and bind to host receptors. A. Annotate the representation below to briefly describe each process associated with a numbered label. B. Describe influenza A viral replication as a process regulated by either positive or negative feedback and justify your selection. The human-acquired immunodeficiency syndrome (AIDS) and many cancers are cause by double-stranded RNA retroviruses C. Contrast the processes of viral replication of HIV and influenza A virus. D. Explain the difference in the effects of infection by HIV and influenza A virus on host genetic variability. E. Measured mutation rates for influenza A virus and HIV are nearly identical (Sanjuan et al., Jour. Virology, 2010). Explain this observation even though host error-checking operates in one of these replication modes
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