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21 Cards in this Set
- Front
- Back
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What is a virus?
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Sub microscopic entities consisting of a single nucleic acid surrounded by a protein coat and capable of replication only within the living cells of bacteria, animals, or plants.
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What are the 3 components that ALL viruses must have or make?
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1. DNA or RNA genome (never both)
2. Polymerase protein to replicate genome 3. Capsid Protein that forms a core around the genome and provides protection |
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What are 3 components that viruses only sometimes have?
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1. A lipid membrane
2. Virally encoded "spike" protein to attach to target 3. Proteins that modulate the host in some way |
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What type of pathogen is a virus?
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An obligate intracellular pathogen
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What are the 2 phases of a virus life cycle?
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1. Extracellular phase - virus is metabolically inert
2. Intracellular phase - production of new viral progeny |
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What are the 6 genomic classifications of viruses?
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1. Double Stranded DNA
2. Single Stranded + sense DNA 3. Double Stranded RNA 4. Single Stranded + sense RNA 5. Single Stranded - sense RNA 6. Reverse Transcriptase - Single + sense RNA --> DNA |
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What are the 2 practical implications of RNA vs. DNA viruses?
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1. RNA Polymerases don't have proofreading function. Thus, RNA virsues tend to mutate more than DNA viruses
2. RNA viruses tend to replicate quickly (especially + sense), since their genome is basically mRNA. Usually cause ACUTE infection |
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What are the 4 ways in which viruses conserve "genetic space"?
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1. Polyprotein production - 1 promoter for multiples genes. Polyproteins is then cleaved using PROTEASE
2. RNA Splicing 3. Overlapping reading frames - start codons in different locations gives different proteins 4. Ribosomal frameshifting - ribosomal slippage gives new reading frames which translate different proteins |
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What are the 2 main types of viral capsids?
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1. Helical - always surrounded by a lipid membrane
2. Icosahedral - usually naked or surrounded by an envelope |
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What is the main function of a viral capsid?
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To protect and transport the viral genome
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How do enveloped viruses aquire their lipid membrane?
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Via budding from the host cell
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What structures are located on the membrane surface of an enveloped virus?
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"Spike" glycoproteins - Attach virus to cell surface. Also get virus into cell
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How are envelope viruses transmitted?
Non-envelope? |
Enveloped - not stable outside body so transmitted via body fluids
Nonenveloped - stable outside of body so can spread in other means such as fecal-oral, doorknobs, etc. |
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What are the 6 basic steps in the life cycle of ANY virus?
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1. Attachment - virus binds receptor
2. Penetration 3. Uncoating 4. Translation/Transcription/Replication 5. Assembly 6. Release |
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What kinds of molecules can be virus receptors?
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All sorts of host cell surfact proteins
Ex: Sialic acid, integrins, LDL, etc |
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What is viral tropism?
What explains it? |
The spectrum of tissues and cell types infected by a given virus
- Often explained by presence/absence of viral receptor |
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What are the 3 ways viruses can enter a host cell?
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1. Membrane Fusion - all enveloped viruses use this
2. Pore formation 3. Membrane Lysis - enter cell via endocytosis then lyse vacuole to enter cytoplasm |
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What is a major signal to virus during penetration step?
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pH changes
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What are the 3 major mechanisms by which viruses mutate?
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1. Simple Mutations - normal, error in bp during replication
2. Recombination - Happens during replication of DNA viruses 3. Reassortment - happens when 2 viruses infect same call. Genomes can get shuffled around, mixed up. |
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What do packaging signals in the viral genome do?
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Stem-loop structures on viral DNA/RNA that signal that it is viral DNA/RNA and not host cell DNA/RNA
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How are enveloped viruses released from the cell?
Nonenveloped? |
Enveloped - bud from cellular membrane
Nonenveloped - assemble in cells, and continue to do so until the cell lyses and they are released |
