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2 Viruses
June 18
18
Biology
Undergraduate 2
06/18/2015

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Term
What is a virus?
Definition
◦ Obligate intercellular parasites
◦ Consist of DNA or RNA genome and protein coat
Term
What is the shape and make up of a virus?
Definition
diversity of structure and genetic material
Term
What are 4 types of viruses and their shapes?
Definition
Tobacco mosaic virus-capsomere of capsid made of RNA
Adenovirus--capsomere of DNA in the form of a stop sign
Influenza virus-Made up of RNA a circle of clycoproteins, membranous envelope with capsid and Rna on the inside
Bacteriophage T4-head, tail sheath, tail fiber
Term
What are the 6 classes of animal viruses?
Definition
dsDNA- Double stranded DNA
ssDNA- Single stranded DNA
dsRNA- Double stranded RNA
ssRNA- Single Stranded RNA
ssRNA- Template for mRNA Synthesis
ssRNA-Template for DNA synthesis
Term
What is the life cycle of the virus?
Definition
1-Entry and uncoating
2-Replication
3-Transcription and manufacture of capsid protein
4-Self-assembly of new virus particles and their exit from the cell
(deeper understanding)
 Viral genome infects cell
 Uncoats
 Uses host machinery to:
 Replicate genome
 Express viral proteins
 Virus particles self-assemble
 Virus exits host cell
 Most damage occurs on exit
 In some cases transcriptional regulation of cellular genes
is altered by viral insertion into host genome or by virusderived
transcription factors → cancer
Term
What are bacteriophages?
Definition
bacterial viruses
Term
what does the lytic cycle result in?
Definition
host cell lysis
Term
describe the lysogenic cycle
Definition
 Integrates into host genome
 Doesn’t kill cell
 Can become lytic later
Term
What is a capsid?
Definition
◦ Protein shell around virus
 Diverse in shape and size
Term
What is an envelope?
Definition
◦ Present in some viruses
◦ Membrane around capsid
◦ Derived from host membrane
◦ Contains glycoproteins
 Help virus infect other cells
Term
Describe host range
Definition
◦ Viruses infect specific species and
specific tissues
 Due to molecules on viruses
interacting with specific host cellsurface
proteins
◦ Can be broad or narrow
 West Nile Virus infects birds,
mammals, even alligators.
Particularly deadly in corvids (crows,
magpies), horses
 Polio is human-specific – wipe it out
in humans and it will be gone for
good
Term
What are treatments for viral infection?
Definition
◦ Vaccination
 Use hobbled virus to raise antibodies that will attack
virus and keep it from infecting cells
 Example: small pox, flu
◦ Treat symptoms
 Example: cold
◦ Slow progression of infection
 Example: HIV
Term
What is a retrovirus?
Definition
◦ Require RNA to be copied
to DNA
 Reverse Transcriptase (RT,
RTase)
◦ Example:
 Human immunodeficiency
virus (HIV)
Term
Describe HIV
Definition
◦ Invades cells of immune system
 White blood cells
◦ Can exist as provirus
 Integrates into host genome
◦ Reverse transcriptase is error prone
 High mutation rate, fast evolution
 By the time immune system responds,
virus has changed enough not to be
recognized
 Defeats attempts at a vaccine
 Rapidly develops drug resistance
Term
What are people trying to do to treat HIV?
Definition
 Currently available:
 RTase inhibitors
 Premature termination of transcription
 Irreversible inhibition of enzyme
 Protease inhibitors
 Envelope protein must be clipped
 Fusion inhibitors
 Block viral envelope from fusing with cell membrane
 Integration inhibitors
 Prevent DNA copy of virus from inserting into genome
Term
What are RT inhibitors?
Definition
Dideoxynucleotides prevent elongation,
lead to premature termination
Term
What is a protease inhibitor?
Definition
HIV’s mRNA is translated into a single
polypeptide with several domains
One of the domains is a protease (an
enzyme that cuts proteins)
The protease must separate the
domains into individual proteins for
each to function
• capsid
• envelope proteins
• RT
• transcription factors
Protease inhibitor blocks protease,
prevents function of viral proteins
within cell and formation of new virus
Term
What are some problems with treating hiv?
Definition
 Because retroviruses have high mutation rate, they develop
resistance to individual drugs
 Hit with three drugs at once, making it difficult for a single virus
to adapt to all three at the same time
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