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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