Test Answers on Chapter 6 – Microbiology – Flashcards
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| Who first termed the word virus? |
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| Louis Pasteur |
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| In the 1890s it was discovered that diseases were caused by viruses. What was discovered in 1911 that viruses may cause? |
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| Cancer |
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Viruses can infect EVERY type of cell. True or False? |
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| True |
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| Are viruses considered living things? Why or why not? |
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| No because they cannot exist independently from the host cell. But they can direct life processes so they aren't completely lifeless molecules. They're referred to as 'infectious particles' |
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| Like Rickettsia and Chlamydia, viruses are known as... |
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| obligate intracellular parasites |
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| What two external coatings can make up a virus? |
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| Capsid and/or Envelope |
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| If the virus doesn't have an envelope, what is it referred to as? |
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| A naked virus |
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DNA and RNA can be in the core of a virus. True or False. |
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| False. Viruses can have only one or the other. |
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| What do we call a capsid ad the nucleic matter together? |
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| nucleocapsid |
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| What is a virion? |
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| Fully formed virus that is able to establish an infection in a host cell |
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| What is the viral capsid constructed of? |
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| Capsomeres, which are identical subunits made up of protein molecules. |
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| What are the two types of viral capsids? Describe each. |
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| What are complex viruses? |
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| A virus that is shaped other than helical or icosahedral |
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| Where does the viral envelope come from? |
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| The virus steals part of the host cell membrane in the form of an envelope. The regular membrane proteins are replaced with viral proteins. |
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| What is the function of spikes in the viral envelope? |
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| attachment |
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| List 3 functions of the viral capsid/envelope. |
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DNA viruses;are only double stranded. True or false. |
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| False. They can be single stranded or double stranded but most are double stranded. |
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| RNA viruses are mostly single stranded. Describe the difference between positive-sense RNA and negative-sense RNA. |
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| Positive-sense RNA is ready for immediate translation into proteins; negative-sense RNA has to be converted into the proper form before being made into proteins. |
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| What does it mean that RNA viruses are segmented? |
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| Individual genes exist on separate pieces of RNA |
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| Give an example of 4 DNA viruses that are double-stranded and cause cancer. |
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Poxvirus (smallpox) Herpesvirus (HSV1 ; HSV2) Adenovirus Papovavirus (HPV) |
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| What are two enzymes found in a virus? What do they do? |
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Polymerases- synthesize DNA and RNA ; Replicases- copy RNA |
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| Name the steps in the multiplication cycle of a virus. |
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| An exact fit is required for viruses to be able to adsorb into a host cell. True or False? |
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| True- it gives the virus a limited host range |
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| What is meant by endocytosis in the penetration step? |
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| The entire virus is englufed by the host cell and enclosed in a vacuole or vesicle |
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| What is the other way a virus can penetrate into the host cell besides endocytosis? |
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| The viral envelope can directly fuse with the host cell membrane |
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| What occurs in the uncoating stage? |
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| Enzymes in the vacuole dissolve the envelope and capsid and the virus is 'uncoated' |
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| Describe the Synthesis stage of DNA viruses. |
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The viral nucleic acid enters the host cell's nucleus where it's replicated and assembled. ; Specifically, it enters the nucleus, is transcribed into RNA; the RNA becomes a message for synthesizing viral proteins; and the new DNA is synthesized using host nucleotides. |
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| Describe the Synthesis stage for RNA viruses. |
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It is replicated and assembled in the cytoplasm of the host cell. ; *Except for retroviruses |
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| What is unique about the synthesis of retroviruses? What do they contain that allow them to synthesize? |
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| Retroviruses contain reverse transcriptase- an enzyme that takes the RNA virus and makes it into a DNA virus. The virus then synthesizes in the host cell's nucleus |
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| In assmbly, mature virus particles are constructed from the growing pool of parts of the host cell. True or False. |
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| True |
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| How are naked viruses and complex viruses released? |
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| When the cell lyses |
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| Which two ways can an enveloped virus be released? |
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| Budding or exocytosis |
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| What are cytopathic effects? Give two examples. |
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Examples
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| What is meant when a virus maintains a carrier relationship? |
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| The host cell harbors the virus and is not immediately lysed. Some viruses can remain this way chronically, periodically becoming activated. |
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| What is meant by viruses being oncogenic? What's an oncovirus? |
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The virus enters the host cell and permanently alters its genetic material, leading to cancer ; Oncoviruses are mammalian viruses capable of initiating tumors, like retroviruses |
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| What is a virus called when it infects bacteria? How can this affect humans? |
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Bacteriophage (phage for short) ; The bacteria the virus infects becomes more pathogenic for humans |
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| What are temperate phages? |
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| Special DNA phages that undergo adsorption and penetration but aren't replicated or released immediately. The viral DNA enters an inactive prophage stage (copied during normal cell division) |
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| What is lysogeny? |
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When the host chromosome carries bacteriophage DNA
The bacterial cell appears normal
All of this allows the virus to spread without killing the host
Unfortunately this happens with many bacteria that infect humans |
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| What is a lysogenic conversion? |
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| When a bacterium acquires a new trait from its temperate phage |
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| What are two useful ways we can use lytic bacteriophages? |
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1. as an alternative to antibiotic treatment 2. for genetic studies |
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| Why do we cultivate viruses? (3) |
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| What are three ways we cultivate viruses? |
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| What indicates that a virus has killed cells in a cell culture? |
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| plaque |
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| What are HeLa Cells? Who are they from? When? Why were they taken? What is their importance? |
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| HeLa Cells are cells from the woman Henrietta Lacks. She had cells removed from her cervix to see if she had cancer in 1951. Lacks died but her cells still remain alive today in labs all across the world. We use them to grow viruses (50 yrs later) |
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| Viruses are a rare cause of acute infections in humans. True or false? |
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| False- they are the most common but they don't usually result in hospitalization or death. Those that are deadly have high death rates! |
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| What two things are considered when diagnosing a viral disease? |
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Signs and symptoms of patient ; Identification tests to look for cytopathic effects |
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| How do we treat viral infections? (3 ways) |
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| What's gene therapy? Who's example was used in class? |
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A technique for correcting defective genes responsible for disease development-- use viruses that target the nucleus
Ex. Jesse Gelsinger-- give adenovirus modified to possess the OTC gene |
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| What are spongiform encephalopathies? |
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| What are prions? |
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Misfolded proteins (not a virus)
spreads to more and more proteins in the brain, leaving holes |
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| What are satellite viruses? Give an example. |
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Defective forms of viruses that depend on other viruses for replication
Ex. Hepatitis E-- depends on Hep. B |
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| What are viroids? |
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| Parasite plants composed only of naked strands of RNA |
