Glossary of Microbiology Chapter 18
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- How do the "life cycles" of animal viruses compare to those of bacteriophage?
- The "life cycle" of animal viruses consists of different stages: adsorption, penetration and uncoating, aassembly, release, and replication and transcription, comparable to that of bacteriophage
- How do naked (oh my) and enveloped viruses adhere to the cell?
- Adsoroption of virions occurs through a random collision of the virion with a plasma membrane receptro site. Naked viruses bind to receptors at capsid proteins while enveloped viruses bind to receptors at the peplomers/spikes of the envelope. These receptors are usually glycoproteins or (endocytosis) hormone receptors.
- How do enveloped viruses penetrate the cell?
- Enveloped viruses can (1) enter after fusion of the envelope with the plasma membrane or (2) excape from the vesicle after endocytosis. Naked viruses may be taken up by endocytosis and then insert their nucleic acid into the cytoplasm through the vesicle membrane.
- Where do uncoating and encapsidation usually occur?
- Uncoating and encapsidation usually occur in the cytoplasmic matrix (naked viruses insert their DNA into the cytoplasm through the endocytotic vesicle membrane).
- How do naked and enveloped viruses escape from the cell and what is the effect of their release upon the cell?
- Naked:host cell lysis (enzyme mediated)
Enveloped:usually budding at cytoplasm membrane
Effect:Replication and Transcription?
- Why can Parvoviruses use host polymerases but the poxviruses cannot?
- Paroviruses is a small ssDNA genome with replication at the nucleus.
The poxviruses is dsDNA and has a large genome and therefore needs all of its own machinary.
- What are replicases and transcruptases?
- Replicases-an RNA-dependent RNA polymerase.Reads mRNA and makes RNA.
Transcriptases-A viruses-associated RNA-dependent RNA polymerase, which synthesize mRNA, that is employed by +viruses. (makes mRNA)
- What types of virus would be most likely to pack a transcriptase in the capsid?
- What are the normal replicative form of a RNA genome?
- replicase -to- +/- strands (replicative form = a double stranded form of nucleic acid that is formed from a ss virus genome & used to synthesize new copies of the genome)
- How can a monopartite picrnavirus genome encode several proteins?
- It makes a big protein that is clipped into functional units. ?
- What is an evolutionary advantage to a multipartite genome?
- Mix and match packaging can lead to new strands/mutations/variance
- What are retroviruses?
- RNA genome that carry out the enzyme reverse transcriptase to form a DNA copy of their genome.
- Describe the organization and 3 minimal genes of the retroviruses genome.
- Provirus integrates into chromosome. Host then activates transcription of provirus (hnRNA). Differential processing(mRNA).
gag-group antigen (capsid)
pol-polymerase (reverse transctiptase)
- What does Reverse Transciptase do?
- RNA-directed DNA polymerase, DNA-directed DNA polymerase and a ribonuclease
- What gene encodes the protease and integrase? What do they do?
Protease-cleaves polypeptides to proteins.
- Where is the provirus found?
- U3 R U5 gag pol env U3 R U5
- How is the LTR (long terminal repeat) generated? What is the significance of forming the LTR?
- LTR needs to bring promoter 5' into the genome or can't transcribe. Formation of DNA brings U5 downstream of U3R creating LTR
- By what mechanisms can a virus damage a host cell?
- Cytocidal-cell killing
Immune mediated damage-to be discussed in immunology section
Direct damage-many mechanisms
- What is apoptosis (see page 765)?
- Programmed cell death. The fragmentation of a cell into membrane-bound particles that are eliminated by phagocytosis. Physiologocal suicide mechanism that preserves homeostasis.
- What are persistent infections?
- Infections that last a long time. Either Chronic Infection or Latent Infection
- How do chronic infections differ from latent infections?
- Chronic-continuous release of virus usually with signs and symptoms of the infection
Latent-virus remains dormant w/o signs or symptoms
- What are oncoviruses? What is meant by transformation in this context (not in book)
- genes that cause transformation. Mutated genes-normal genes in viral environment.
- What dsDNA viruses and retroviruses are associated with specific cancers? How do they cause cancers?
- What are viroids? What type of host are they found in?
- Only RNA (NO PROTEIN COAT)
Circular ssRNA, but appears as dsRNA due to intrastrand pairing. Replicated by DNA dep. RNA polymerase w/ no evidence of translation. ONLY IN PLANTS! Causes dwarfing
- What are prions? What disease might they cause?
- Proteinaceous infectious particle. Prion diseases are associated with PRPsc (Sc for Scrapie)
- Microbiology: Chapter 18
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