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Micro Unit 4 of 14
Microbiology Study Guide for the CLEP Exam (Viruses and Prions)
| Question | Answer |
|---|---|
| Because viruses are incapable of replicating outside of a host , they are called ______ ______ _______ | obligate intracellular parasites |
| What is the size of the largest virus? | 1/25 the size of the smallest bacterium |
| What are bacterial viruses called? | bacteriophages or just "phages" |
| How does a bacteriophage penetrate the host cell wall? | In addition to the factors they use to adhere to the host cell, they also have a needlelike tube they use to propel through the bacterial envelope and inject their nucleic acid inside the host cell. |
| Define "capsomere" | a viral protien that forms the coat around the viral nucleic acid |
| Define "capsid" | the protien shell made of capsomeres |
| Define "nucleocapsid" | the capsid covering PLUS the nucleic acid |
| Define "envelope" | an additional covering made of membrane from the host cell and viral protiens |
| Define "virion" | an intact viral particle with its appropriate coating layers |
| Define "icosahedron" | twenty identical sides |
| List the two main components of nucleocapsids | the capsid and the nucleic acid |
| what are nonenveloped viruses called? | naked viruses |
| The placement of viruses into families depends upon which characteristics? | structural features: general size and shape, naked or enveloped, and if their nucleic acid is RNA or DNA |
| What part of the envelope comes from the host cell and what part from the virus? | The membrane is from the host and the attachement protiens are from the virus |
| What type of molecule in an enveloped virus is neccessary for attachment to the host cell? | a viral attachment protien that protrudes outside the viral envelope is necessary for attachment to the host cell |
| Adsorbtion of the virus to the cell depends upon what specific viral and cellular components? | viral attachment protien and a cell receptor |
| What are the two types of cell penetration in the life cycle of a human virus? | endocytosis and membrane fusion |
| Where and how does uncoating take place in the life cycle of a human virus? | uncoating is the removal of the viral capsid protien by cellular enzymes in the cell cytoplasm |
| Where does DNA and RNA replication take place in the life cycle of a human virus? | Replication takes place in the cell nucleus for DNA and in the cytoplasm for RNA |
| Where does viral translation occur in the life cycle of a human virus? | in the host cytoplasm |
| How does the assembly of intact virions occurin the life cycle of a human virus? | protiens from the coating bind to each other and to the proper nucleic acid enabling the nucleocapsid to zip together without outside energy |
| Describe how the release of virions can occur by cell lysis or budding in the life cycle of a human virus? | a naked virus simply lyses the cell to release the virions; an eneloped virus acquires a membrane from the host as it passes through the cell membrane |
| How many phages or virions can be produced in a single growth cycle? | about one hundred phages per bacterium and about three hundred thousand animal virions per animal cell can be produced in a single growth cycle |
| How does a lytic virus destroy a cell? | Lytic viruses ALWAYS kill the host cell by breaking it open. |
| How does a lysogenic virus damage a cell? | lysogenic viruses enter the cell where the DNA integrates into a host cell and becomes part of it; then they divide with that cell. If the host cell becomes sick, lysogenic viruses become lytic and escape the dying cell |
| What are cytopathic effects? | cytopathic effect refers to visible changes, microspopic or otherwise, in cells resulting from viral infection. cytopathic effects occur when a viral specimen is placed in human tissue cells in a cultural medium |
| What is plaque? | it's a specific type of CPE where cells are killed so that loss of cells give rise to a hole in the cell layer |
| How is the inclusion body type of CPE observed? | Inclusion bodies are normally seen in the microscope as dark areas of viral material |
| What are the resulting large cells called when many cells fuse together as a result of viral infection? | the large cells are called syncytia or "giant" cells |
| What changes occur during transformation? | viruses cause the cells to keep growing uncontrollably and pile up to form a tumor |
| What do viruses do to the host DNA-synthesizing machinery? | viruses subvert the host cell machinery into making viruses rather than cellular materials |
| What type of nucleic acid is in a virion? | Either RNA or DNA, but not both! |
| Why is tumorigenisis only associated with DNA viruses or retroviruses? | tumorgenesis only occurs when a cell's genes are altered to cause uncontrollable cell division. ONLY DNA can integrate into the cell's chromosome because the chromosome IS DNA |
| Describe the smallest biological agent that is replicated. | a prion is a protien that causes itself to be replicated by the way it folds |
| What damage do prions do? | abnormally folded prion protiens accumulate in the brain until the brain tissue is destroyed and the host dies |
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