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Chapter 6
Viruses
52
Microbiology
Undergraduate 1
07/19/2011

Additional Microbiology Flashcards

 


 

Cards

Term
Who first termed the word virus?
Definition
Louis Pasteur
Term
In the 1890s it was discovered that diseases were caused by viruses. What was discovered in 1911 that viruses may cause?
Definition
Cancer
Term

Viruses can infect EVERY type of cell.

True or False?

Definition
True
Term
Are viruses considered living things? Why or why not?
Definition
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'
Term
Like Rickettsia and Chlamydia, viruses are known as...
Definition
obligate intracellular parasites
Term
What two external coatings can make up a virus?
Definition
Capsid and/or Envelope
Term
If the virus doesn't have an envelope, what is it referred to as?
Definition
A naked virus
Term

DNA and RNA can be in the core of a virus.

True or False.

Definition
False. Viruses can have only one or the other.
Term
What do we call a capsid ad the nucleic matter together?
Definition
nucleocapsid
Term
What is a virion?
Definition
Fully formed virus that is able to establish an infection in a host cell
Term
What is the viral capsid constructed of?
Definition
Capsomeres, which are identical subunits made up of protein molecules.
Term
What are the two types of viral capsids? Describe each.
Definition
  1. Helical- rod shaped capsomeres (not usually human viruses)
  2. Icosahedral- 3D, 20 sided figure with 12 evenly spaced corners; wide variations
Term
What are complex viruses?
Definition
A virus that is shaped other than helical or icosahedral
Term
Where does the viral envelope come from?
Definition
The virus steals part of the host cell membrane in the form of an envelope. The regular membrane proteins are replaced with viral proteins.
Term
What is the function of spikes in the viral envelope?
Definition
attachment
Term
List 3 functions of the viral capsid/envelope.
Definition
  • Protect nucleic acids
  • Help introduce the viral DNA or RNA into a suitable host cell
  • Stimulate the immune system to produce antibodies that can protect the host cells against future infections
Term

DNA viruses are only double stranded.

True or false.

Definition
False. They can be single stranded or double stranded but most are double stranded.
Term
RNA viruses are mostly single stranded. Describe the difference between positive-sense RNA and negative-sense RNA.
Definition
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.
Term
What does it mean that RNA viruses are segmented?
Definition
Individual genes exist on separate pieces of RNA
Term
Give an example of 4 DNA viruses that are double-stranded and cause cancer.
Definition

Poxvirus (smallpox)

Herpesvirus (HSV1 & HSV2)

Adenovirus

Papovavirus (HPV)

Term
What are two enzymes found in a virus? What do they do?
Definition

Polymerases- synthesize DNA and RNA

 

Replicases- copy RNA

Term
Name the steps in the multiplication cycle of a virus.
Definition
  1. Adsorption
  2. Penetration
  3. Uncoating
  4. Synthesis
  5. Assembly
  6. Release
Term
An exact fit is required for viruses to be able to adsorb into a host cell. True or False?
Definition
True- it gives the virus a limited host range
Term
What is meant by endocytosis in the penetration step?
Definition
The entire virus is englufed by the host cell and enclosed in a vacuole or vesicle
Term
What is the other way a virus can penetrate into the host cell besides endocytosis?
Definition
The viral envelope can directly fuse with the host cell membrane
Term
What occurs in the uncoating stage?
Definition
Enzymes in the vacuole dissolve the envelope and capsid and the virus is 'uncoated'
Term
Describe the Synthesis stage of DNA viruses.
Definition

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.

Term
Describe the Synthesis stage for RNA viruses.
Definition

It is replicated and assembled in the cytoplasm of the host cell.

 

*Except for retroviruses

Term
What is unique about the synthesis of retroviruses? What do they contain that allow them to synthesize?
Definition
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
Term
In assmbly, mature virus particles are constructed from the growing pool of parts of the host cell. True or False.
Definition
True
Term
How are naked viruses and complex viruses released?
Definition
When the cell lyses
Term
Which two ways can an enveloped virus be released?
Definition
Budding or exocytosis
Term
What are cytopathic effects? Give two examples.
Definition
  • damage to the cell that alters its microscopic appearance

Examples

  • Inclusion bodies- compacted masses of viruses or damaged cell organelles
  • Syncytia- fusion of multiple host cells into single large cell containing multiple nuclei
Term
What is meant when a virus maintains a carrier relationship?
Definition
The host cell harbors the virus and is not immediately lysed. Some viruses can remain this way chronically, periodically becoming activated.
Term
What is meant by viruses being oncogenic? What's an oncovirus?
Definition

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

Term
What is a virus called when it infects bacteria? How can this affect humans?
Definition

Bacteriophage (phage for short)

 

The bacteria the virus infects becomes more pathogenic for humans

Term
What are temperate phages?
Definition
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)
Term
What is lysogeny?
Definition

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

Term
What is a lysogenic conversion?
Definition
When a bacterium acquires a new trait from its temperate phage
Term
What are two useful ways we can use lytic bacteriophages?
Definition

1. as an alternative to antibiotic treatment

2. for genetic studies

Term
Why do we cultivate viruses? (3)
Definition
  • to isolate and ID viruses in clinical specimens
  • to prepare viruses for vaccines
  • to do detailed research on viral structure, multiplication cycles, genetics, and effects on host cells
Term
What are three ways we cultivate viruses?
Definition
  1. Animal inoculation
  2. Bird embryos (ex. flu vaccine)
  3. Cell (tissue) culture-- most used
Term
What indicates that a virus has killed cells in a cell culture?
Definition
plaque
Term
What are HeLa Cells? Who are they from? When? Why were they taken? What is their importance?
Definition
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)
Term
Viruses are a rare cause of acute infections in humans. True or false?
Definition
False- they are the most common but they don't usually result in hospitalization or death. Those that are deadly have high death rates!
Term
What two things are considered when diagnosing a viral disease?
Definition

Signs and symptoms of patient

 

Identification tests to look for cytopathic effects

Term
How do we treat viral infections? (3 ways)
Definition
  • Antiviral drugs- block virus replication by targeting a step in its life cycle
  • Interferon has shown potential for treatment and prevention
  • Vaccines- stimulate immunity
Term
What's gene therapy? Who's example was used in class?
Definition

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

Term
What are spongiform encephalopathies?
Definition
  • Chronic, persistant disease with a long period of latency
  • Deposits prions into brain tissue causing mad cow disease, scrapie, CJD
Term
What are prions?
Definition

Misfolded proteins (not a virus)

 

spreads to more and more proteins in the brain, leaving holes

Term
What are satellite viruses? Give an example.
Definition

Defective forms of viruses that depend on other viruses for replication

 

Ex. Hepatitis E-- depends on Hep. B

Term
What are viroids?
Definition
Parasite plants composed only of naked strands of RNA
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