Viruses – Microbiology Answers – Flashcards
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| Viruses are composed of: |
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| DNA or RNA A protein coat |
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| Are viruses living? |
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| NO. They have no metabolism, cannot reproduce on their own, and do not respond to stimuli. |
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| How do viruses relate to gene therapy? |
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| Since viruses are built to inject DNA into a host cell, we can use them as vectors to deliver beneficial DNA to patients with genetic diseases. |
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| Particle |
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| Another name for "virus" |
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| Virion |
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| Viruses existing outside a host. Also, sometimes viral "progeny" |
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| How to see a virus? |
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| Electron microscope - most are too small to be seen through light microscopy |
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| Capsid |
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| Protein "coat" made of capsomer units that surrounds viral genetic material |
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| Envelope |
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| Stolen bit of cellular membrane that some viruses take upon leaving a host cell. They do not usually contain host cell proteins, which means that viruses can remove them somehow. |
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| How is a viral genome set up? |
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| Because of space limitations, there is no noncoding DNA/RNA. Genes may be overlapping (read in different reading frames), and the strand can be read forwards OR backwards. |
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| Virus class 1 |
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| Double-stranded DNA |
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| Virus class 2 |
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| Single-stranded DNA |
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| Virus class 7 |
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| Double-stranded DNA that replicates through an RNA intermediate |
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| Virus class 3 |
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| Double-stranded RNA |
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| Virus class 4 |
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| Positive-sense single-stranded RNA |
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| Virus class 5 |
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| Negative-sense single-stranded RNA |
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| Virus class 6 |
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| Single-stranded RNA that replicates through a DNA intermediate. HIV is in this category. |
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| Positive-sense |
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| Viral RNA that is read and translated directly |
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| Negative-sense |
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| Viral RNA that has to be made into a complementary copy before it can be translated |
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| Dr. David Baltimore |
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| Developer of the Baltimore scheme, a classification scheme for viruses |
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| Capsomers |
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| Subunits of a capsid. They tend to self-assemble due to physical properties that make them "click" together. Capsomers in a capsid may be different than one another or all the same. |
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| Nucleocapsid |
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| A capsid that is associated with nucleic acid |
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| Helical viruses |
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| Rod-shaped viruses that are coated in a single capsomer type. No known human pathogens. |
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| Icosahedral viruses |
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| Spherical viruses with homogeneous or heterogeneous types of capsomers. Since they aren't smooth circles, think geodesic domes. |
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| Enveloped viruses |
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| Icosahedral or helical viruses that snag part of the host cell membrane when budding out. |
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| Peplomers |
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| Viral "spikes" that protrude out from the viral surface through an envelope. They help the virus masquerade as a benign particle. |
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| Complex viruses |
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| "Head and tail" morphology. |
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| Function of an outer shell for a virus |
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| Protection from the external environment Assistance in host cell docking |
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| Adsorption |
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| Virus encounters and attaches to proteins on a target cell |
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| Host range |
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| The total pool of cells that a virus can infect and replicate inside |
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| Tropism |
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| Tissue preference of a virus |
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| Restricted host range |
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| One type of cell. Example: Hepatitis only infects liver cells (hepatocytes). |
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| Intermediate host range |
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| Virus infects several cell types. Example: Chickenpox can infect epithelial and nervous cells. |
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| Broad host range |
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| Virus infects all cell types. Example: Cytomegalovirus, which has been with humans so long that it has adapted to infect all our cell types. Because we're so used to it, the virus causes no symptoms. |
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| Penetration |
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| The virus enters the cell. Either the whole virus can enter (through membrane fusion or endocytosis) or only the nucleic acids. |
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| Uncoating |
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| Removal of nucleic acids from the virus. This can occur during or after penetration. |
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| Synthesis |
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| Viral nucleic acids commandeer cellular transcription equipment. For DNA viruses, this happens in the nucleus, for RNA viruses, in the cytosol. |
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| Virus latency |
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| Double-stranded DNA viruses can integrate themselves into the host cell genome. When they do this, they become "latent" and are not transcribed until later. |
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| How can viruses cause cancer? |
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| When viruses go latent, they integrate their DNA into a random spot in the host genome. If that random spot happens to be in the middle of an oncogene (tumor suppressor gene), the cell will lose the ability to control its growth and replication. |
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| Provirus |
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| DNA form of retroviral RNA, which is integrated into the host cell genome |
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| Assembly |
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| Transcription and translation of viral genetic material. |
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| Integrase |
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| Helps viral DNA integrate into the host cell genome |
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| Protease |
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| Clips protein chains into useable units |
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| Release |
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| Viral progeny leave the cell. Naked (no envelope) viruses do this by lysing the cell, enveloped viruses do this by budding or exocytosis |
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| Bacteriophages |
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| Viruses that attack bacteria, usually double-stranded. They can carry toxins that can make bacteria more virulent. |
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| Lytic replication |
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| The virus undergoes normal replication. |
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| Lysogenic replication |
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| Virus enters the host cell and becomes latent. Later, it replicates. |
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| Temperate phages |
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| Phages that undergo lysogenic replication |
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| Prophage |
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| Phage DNA that is integrated into bacterial genome |
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| Why would a virus undergo lysogenic replication over lytic replication? |
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| By integrating into the host genome and waiting for the cell to divide, a single virus can effectively infect many cells at once, which in turn can produce more viruses. |
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| Lysogenic conversion |
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| A change in the properties of a bacterial host by a virus. |
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| Why would a virus want to perform lysogenic conversion? |
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| A bacteria that has an advantage (like a toxin, given by a virus) will be able to fight back against the immune system and reproduce more successfully, giving the virus more places to replicate. |
