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81 Cards in this Set
- Front
- Back
Are viruses susceptible to antibiotics?
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No
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Can viruses synthesize their own proteins?
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No
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Do viruses generate their own metabolic energy
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No
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What is the mode of reproduction for viruses?
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Host cell synthesis of subunits then assemble them into iron
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Does virus compromise of DNA or RNA?
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Either but not both
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Virion
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Mature infectious virus particle
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Capsid
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Protein shell that encloses and protects the viral nucleic acid
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Capsomer
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Polymers of polypeptide chains
Morphological units of capsid |
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Nucleocapsid
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Internal part of virus particle - consists of nucleic acid
Closely associated proteins Used when this complex is a discrete substructure of a complex particle |
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Envelope
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The viral membrane - consists of lipid bilayer, proteins, and glycoproteins
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+ssRNA
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Single stranded RNA of the same polarity as mRNA
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-ssRNA
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Single stranded RNA complementary to mRNA
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DNA dependent RNA polymerase
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Enzyme that uses DNA as a template for producing RNA
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RNA dependent RNA polymerase
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Enzyme that uses RNA as a template for producing RNA
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Are RNA dependent RNA polymerase found in host cells?
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No, viruses use this to make mRNA and RNA genomes
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DNA dependent DNA polymerase
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Enzyme that uses DNA as template for producing DNA (our cells use this to replicate)
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RNA dependent DNA polymerase
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Enzyme that uses RNA as the template for producing DNA
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What is an example of RNA dependent DNA polymerase?
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Reverse transcriptase in retroviruses and HepB
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cDNA
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Complementary DNA made from RNA by recombinant procedures
Can be cloned Made by reverse transcriptase |
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Transfection
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Infection of mammalian cells by bare viral nucleic acid
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Transformation
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Stable heritable change in genetic makeup and phenotype of a cell resulting from infection of that cell by a virus
Usually implies converting to a neoplastic phenotype |
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Permissive cells
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Cells that supper the complete virus life cycle, with production of infectious virus particles
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Nonpermissive cells
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Cells which permit none of or only part of the virus life cycle
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How are non permissive cells usually transformed?
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By viruses (Applies esp. to DNA viruses)
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Defective Virus
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Virus that is not capable of going through its entire replication cycle unless the cell is infected with a complete virus (helper) particle as well
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Cytopathic effect (CPE)
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Observable damage to a cell resulting from virus infection
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Are animal viruses visible under light microscope? Electron microscope?
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Electron microscope only
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Can a virus have both DNA and RNA as its genetic material?
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No. Only either DNA OR RNA
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What is the structure of viral genomes?
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Can be segmented or a whole single piece
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What makes up the envelope of a virus?
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Host derived phospholipid bilayer
Virus derived proteins and glycoproteins for attachment and viral fusion |
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Which is weaker- enveloped or naked viruses? Why?
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Enveloped viruses = Weaker
B/c envelopes can be inactivated by lipid solvents, and these viruses cannot function without their lipid components |
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What are M proteins? Are they found on all viruses
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Matrix proteins - Aid in viral structure
Only in enveloped proteins |
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What are F proteins? Are they found in all viruses?
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Fusion proteins - cause fusion between viral and cellular membranes
Only in enveloped proteins |
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What are the 5 criteria to classify human viruses?
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1. Chemical structure of the nucleic acid
2. Symmetry of the nucleocapsid 3. Presence of an envelope 4. Dimensions of the virion and capsid 5. Nucleic acid sequence similarities |
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What are the three types of capsids? Which is the least common
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1. Complex - least common
2. Icosahedral 3. Helical |
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Were are complex capsids found? What's its shape?
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In Poxviruses.
Dumbell |
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What is the shape of icosahedral capsid?
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20 triangular faces --> almost like a sphere
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What's special about a helical capsids?
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They always have an envelope
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What is the Penton on an Adenovirus?
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It mediates attachment of the adenovirus to the host cell
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What are the four steps for viral infection of a host cell?
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1. Attachment to the host cell
2. Entry of virus into the host celll 3. Synthesis of viral proteins and genome 4. Assembly and release |
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What is the most important determinant of host specificity in viral attachment?
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Presence of specific viral receptors on host cells
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What cells do HIV infect? What is the receptor HIV recognizes on these cells?
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Macrophages and T cells
Receptor is CD4 |
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How does HIV induce a T cell response?
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By binding to MHCII
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What receptors does HIV bind to? Does it need to bind to all of these to enter the cell?
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Cxcr4 and Ccr5
No. It just needs to bind to either one |
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What is Cxcr4 and Ccr5's normal function?
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Chemokine receptors on immune cells
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What other proteins does HIV use to bind to the host cell?
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SU and TM
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What are the two ways non-enveloped viruses can enter its host cell?
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1. Binds to host cell surface and rearranges capsid protein
2. Receptor mediated endocytosis of virus --> breakup of capsid --> migration into cytoplasm |
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What are the two ways enveloped viruses can enter its host cell?
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1. Fusion of viral membrane and host cell membrane by F protein
2. Phagocytosis and fusion of viral membrane and phagosome membrane by F protein |
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Is F protein required for enveloped virus function?
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YES
Without it, virus cannot enter cell |
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How does poliovirus (naked) enter host cells?
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Binds to receptors --> endocytosed --> creates a pore --> injects its RNA into cytoplasm
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How does Adenovirus enter the cell?
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Penton base interacts with integrin receptor --> endocytosis --> pentons disassemble --> capsid enters cytoplasm and docks on nuclear pore --> viral DNA enters nucleus
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How does Paramyxoviridae (enveloped) enter the cell?
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Envelope fuses with cell membrane --> capsid enters cell
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How does Influenza (DNA) virus enter the cell
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Hemmaglutinin binds sialic acid receptors --> endocytosis --> low pH in endosome --> conformational change --> fusion peptides bring endosome and nuclear membrane close
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How does Semliki Forest virus (RNA) enter the cell?
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Clathrin dependent endocytosis --> acidification -> membrane fuses --> Viral RNA enters cytoplasm --> goes to ribosome for translation
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Which domain of the F protein inserts into the host cell membrane?
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hydrophobic domain
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How does HIV enter cells?
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SU binds CD4 --> Cxcr4 and Ccr5 binding site is exposed --> SU binds Cxcr4 OR Ccr5 --> conformational change --> fusion peptide enters membrane
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Is Cxcr4 or Ccr5 the coreceptor for T-cell-tropic strains?
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Cxcr4
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Is Cxcr4 or Ccr5 the coreceptor for macrophage-tropic strains?
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Ccr5
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Can an individual be resistant to HIV infection?
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YES
If they are homozygous for deletion for Ccr5 |
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How is a syncytium formed?
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F protein mediates fusion of membranes of adjacent cells --> multinuclate giant cells --> syncytium
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What occurs during the eclipse period of the growth curve of Adenovirus?
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Nucleic acid has entered the cell BUT the cell is not making any new viruses
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What occurs during the latent period of the Adenovirus growth curve?
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Infectious viruses are being made but they are still INSIDE the host cell.
There are no infectious viruses outside the host cell yet. |
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Do viruses typically bring their own enzymes or use host cell enzymes in replication?
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Host cell enzymes
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What is the sequence of events in DNA virus's synthesis of macromolecules
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1. Synthesis of early proteins (enzymes for nucleic acid replication
2. Viral genome synthesis 3. Late protein synthesis (structural proteins) |
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Where do DNA viruses replicate?
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Nucleus
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What is an enzyme that DNA viruses need?
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Host cell RNA polymerase II
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Before a DNA virus does protein synthesis, what must happen?
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Synthesis of viral mRNA
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How does retroviruses (RNA virus) synthesize proteins?
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1. Viral RNA is reverse transcribed into DNA
2. DNA --> mRNA through RNA pol II |
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What is an example of a DNA virus that uses reverse transcriptase?
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Hep B
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Why are Poxviruses an exception to the general rule for protein synthesis of DNA viruses? Why do they do this?
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It brings its own Viral DNA dependent RNA polymerase and viral accessory proteins.
Because it replicates in the CYTOPLASM, not nucleus |
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Can +ssRNA, -ssRNA, and dsRNA initiate viral replication and growth?
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Only +ssRNA b/c it can act as mRNA
-ssRNA and dsRNA have to be converted to +ssRNA |
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Are -ssRNA and dsRNA infectious by themselves?
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NO
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Do -ssRNa and dsRNA have to carry enzymes to produce +ssRNA to become infectious?
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YES
only +ssRNA can act as mRNA |
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Is +ssRNA infectious by itself?
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Yes
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Do all RNA viruses have to encode its own RNA dependent RNA polymerase?
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No,
Retroviruses and +ssRNA viruses do not |
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What do retroviruses have instead?
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RNA directed DNA polymerase
Converts viral RNA into dsDNA |
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What has a higher mutation rate - DNA or RNA? Why?
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RNA -- probably because DNA replication has proofreading function while RNA replication does not
RNA dependent DNA polymerase - even higher mutation rate |
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Where does mRNA synthesis typically occur?
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Cytoplasm
May occur in nucleus (Influenza) |
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How do RNA viruses have more heterogeneity in the order of their genes transcribed and proteins produced?
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They can have segmented genomes that can "shuffle" in an infected host cell
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What are the 3 things virion protein shells can be produced from?
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1. Individual polypeptides
2. Polyprotein precurosor then cleaved into smaller functional viral proteins 3. Chaperone mediated |
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What are the two mechanisms of assembly and release of viruses?
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1. Bursting of cell - more common for naked viruses
2. Slow release of virus - with an envelope as the nucleocapsid buds through a virus modified cellular membrane (Ex: HepB) |