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Viruses
Dr. David Senchina, Drake University, Medical Microbio notes set 2
51
Microbiology
Undergraduate 2
02/11/2010

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Term
Viruses are composed of:
Definition
DNA or RNA
A protein coat
Term
Are viruses living?
Definition
NO. They have no metabolism, cannot reproduce on their own, and do not respond to stimuli.
Term
How do viruses relate to gene therapy?
Definition
Since viruses are built to inject DNA into a host cell, we can use them as vectors to deliver beneficial DNA to patients with genetic diseases.
Term
Particle
Definition
Another name for "virus"
Term
Virion
Definition
Viruses existing outside a host. Also, sometimes viral "progeny"
Term
How to see a virus?
Definition
Electron microscope - most are too small to be seen through light microscopy
Term
Capsid
Definition
Protein "coat" made of capsomer units that surrounds viral genetic material
Term
Envelope
Definition
Stolen bit of cellular membrane that some viruses take upon leaving a host cell. They do not usually contain host cell proteins, which means that viruses can remove them somehow.
Term
How is a viral genome set up?
Definition
Because of space limitations, there is no noncoding DNA/RNA. Genes may be overlapping (read in different reading frames), and the strand can be read forwards OR backwards.
Term
Virus class 1
Definition
Double-stranded DNA
Term
Virus class 2
Definition
Single-stranded DNA
Term
Virus class 7
Definition
Double-stranded DNA that replicates through an RNA intermediate
Term
Virus class 3
Definition
Double-stranded RNA
Term
Virus class 4
Definition
Positive-sense single-stranded RNA
Term
Virus class 5
Definition
Negative-sense single-stranded RNA
Term
Virus class 6
Definition
Single-stranded RNA that replicates through a DNA intermediate. HIV is in this category.
Term
Positive-sense
Definition
Viral RNA that is read and translated directly
Term
Negative-sense
Definition
Viral RNA that has to be made into a complementary copy before it can be translated
Term
Dr. David Baltimore
Definition
Developer of the Baltimore scheme, a classification scheme for viruses
Term
Capsomers
Definition
Subunits of a capsid. They tend to self-assemble due to physical properties that make them "click" together. Capsomers in a capsid may be different than one another or all the same.
Term
Nucleocapsid
Definition
A capsid that is associated with nucleic acid
Term
Helical viruses
Definition
Rod-shaped viruses that are coated in a single capsomer type. No known human pathogens.
Term
Icosahedral viruses
Definition
Spherical viruses with homogeneous or heterogeneous types of capsomers. Since they aren't smooth circles, think geodesic domes.
Term
Enveloped viruses
Definition
Icosahedral or helical viruses that snag part of the host cell membrane when budding out.
Term
Peplomers
Definition
Viral "spikes" that protrude out from the viral surface through an envelope. They help the virus masquerade as a benign particle.
Term
Complex viruses
Definition
"Head and tail" morphology.
Term
Function of an outer shell for a virus
Definition
Protection from the external environment
Assistance in host cell docking
Term
Adsorption
Definition
Virus encounters and attaches to proteins on a target cell
Term
Host range
Definition
The total pool of cells that a virus can infect and replicate inside
Term
Tropism
Definition
Tissue preference of a virus
Term
Restricted host range
Definition
One type of cell.
Example: Hepatitis only infects liver cells (hepatocytes).
Term
Intermediate host range
Definition
Virus infects several cell types.
Example: Chickenpox can infect epithelial and nervous cells.
Term
Broad host range
Definition
Virus infects all cell types.
Example: Cytomegalovirus, which has been with humans so long that it has adapted to infect all our cell types. Because we're so used to it, the virus causes no symptoms.
Term
Penetration
Definition
The virus enters the cell. Either the whole virus can enter (through membrane fusion or endocytosis) or only the nucleic acids.
Term
Uncoating
Definition
Removal of nucleic acids from the virus. This can occur during or after penetration.
Term
Synthesis
Definition
Viral nucleic acids commandeer cellular transcription equipment. For DNA viruses, this happens in the nucleus, for RNA viruses, in the cytosol.
Term
Virus latency
Definition
Double-stranded DNA viruses can integrate themselves into the host cell genome. When they do this, they become "latent" and are not transcribed until later.
Term
How can viruses cause cancer?
Definition
When viruses go latent, they integrate their DNA into a random spot in the host genome. If that random spot happens to be in the middle of an oncogene (tumor suppressor gene), the cell will lose the ability to control its growth and replication.
Term
Provirus
Definition
DNA form of retroviral RNA, which is integrated into the host cell genome
Term
Assembly
Definition
Transcription and translation of viral genetic material.
Term
Integrase
Definition
Helps viral DNA integrate into the host cell genome
Term
Protease
Definition
Clips protein chains into useable units
Term
Release
Definition
Viral progeny leave the cell. Naked (no envelope) viruses do this by lysing the cell, enveloped viruses do this by budding or exocytosis
Term
Bacteriophages
Definition
Viruses that attack bacteria, usually double-stranded. They can carry toxins that can make bacteria more virulent.
Term
Lytic replication
Definition
The virus undergoes normal replication.
Term
Lysogenic replication
Definition
Virus enters the host cell and becomes latent. Later, it replicates.
Term
Temperate phages
Definition
Phages that undergo lysogenic replication
Term
Prophage
Definition
Phage DNA that is integrated into bacterial genome
Term
Why would a virus undergo lysogenic replication over lytic replication?
Definition
By integrating into the host genome and waiting for the cell to divide, a single virus can effectively infect many cells at once, which in turn can produce more viruses.
Term
Lysogenic conversion
Definition
A change in the properties of a bacterial host by a virus.
Term
Why would a virus want to perform lysogenic conversion?
Definition
A bacteria that has an advantage (like a toxin, given by a virus) will be able to fight back against the immune system and reproduce more successfully, giving the virus more places to replicate.
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