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40 Cards in this Set

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  • Back
Are viruses considered ultramicroscopic?
Yes. Their size relegates them to the realm of the ultramicroscopic. This means that most of them are so minute(<0.2um) that an electron microscope is necessary to detect them.
More than 2,000 bacterial viruses could fit into an average bacterial cell, and more than 50 million polioviruses could be accommodated by an average human cell. TRUE/FALSE
List the size of several viruses.
Herpes simplex-150nm
T2 bacteriophage-65nm
Yellow fever-22nm
(Hemoglobin molecule-15nm)
Can viruses be stained?
Yes. In combination with electron microscopy, negative staining uses very thin layers of an opaque salt to outline the shape of the virus against a dark background and to enhance textural features on the viral surface. Internal details require positive staining.
What is a nucleocapsid/
Together the capsid and the nucleic acid are referred to as the nucleocapsid. Thirteen of the 20 families of animal viruses possess an additional covering external to the capsid is called an envelope.
What is a naked virus?
Viruses that consist of only a nucleocapsid.
A fully formed virus that is able to establish an infection in a host cell is often called a virion. TRUE/FALSE
What is a capsid?
The capsid appears as the most prominent geometric feature. Each capsid is constructed from identical subunits called "capsomeres".
What are the 2 different types of capsomeres?
Helical capsids have rod shaped capsomeres that bond together to form a series of hollow discs resembling a bracelet.
The capsids of a number of major virus families are arranged in an icosahedron, a three dimensional 20 sided figure with 12 evenly spaced corners.
Can icosahedral viruses have major variations in the number of capsomers?
Yes. A poliovirus has 32, and an adenovirus has 240 capsomers.
Another factor that alters the appearance of icosahedral viruses is whether or not they have an outer envelope. TRUE/FALSE
TRUE. Contrast a papillomavirus(warts) and its naked nucleocapsid with herpes simplex(cold sores) and its enveloped nucleocapsid.
When enveloped viruses(mostly animal) are released from the host cell, they take with them a bit of its membrane system in the form of an envelope. TRUE/FALSE
What are viral spikes?
Some proteins form a binding layer between the envelope and capsid of the virus, and glycoproteins remain exposed on the outside of the envelope. These protruding molecules called spikes or peplomers, are essential for the attachment of viruses to the next host cell.
The capsids of enteric viruses such as polio and hepatitis A are resistant to the acid and protein digesting enzymes of the GI tract. TRUE/FALSE
What are complex viruses?
These are more intricate in structure than the helical, icosahedral, naked or enveloped viruses. The Pox virus are large DNA viruses that lack a regular capsid and have in its place several of lipoproteins and course surface fibrils.
How do viral genes compare with eucaryotic genes?
Viruses must pack into a tiny space all of the genes necessary to instruct the host cell to make new viruses. The number of viral genes is quite small compared with that of a cell. It varies from 4 genes in hepatitis B virus to hundreds of genes in some herpesviruses.
The bacterium E. coli has app. 4000 genes, and a human cell has app 30-40,000 genes. TRUE/FALSE
Are all DNA viruses double starnded, and all RNA viruses single stranded?
No. The parvoviruses, which have single stranded DNA, and Reoviruses(resp and intestinal infections) contain double stranded RNA.
What is positive sense RNA?
Single stranded RNA genomes that are ready for immediate translation into proteins. Other RNA genomes have to be converted into the proper form to be made into proteins, and these are negative sense RNA. RNA genomes may be segmented. The influenza virus is segmented(orthomyxovirus).
Can viruses contain specific enzymes for specific operations?
Yes. Examples include "polymerases", that synthesize DNA and RNA and "replicases" that copy RNA.
The HIV virus has "reverse transcriptase" for synthesizing DNA from RNA.
What are the 6 general phases in the life cycle of animal viruses?
What is the app time for life cycle duration?
The length of the entire life cycle varies from 8 hours in polioviruses to 36 hours in herpesvirus.
List 6 DNA viruses.
List some RNA viruses.
What is a viral tropism/
Viruses usually have tissue specificities called tropisms. Hepatitis B for the liver.
In general, the DNA viruses(except poxviruses) enter the host cells nucleus and are replicated and assembled there. With few exceptions(retroviruses), RNA viruses are replicated and assembled in the cytoplasm. TRUE/FALSE
About 3-4,000 virions are released from a single cell infected with poxviruses, whereas a polio infected cell can release over 100,000 virions. TRUE/FALSE
What are viral cytopathic effects?
They are defined as virus induced damage to the cell that that alters it microscopic appearance. cells become disoriented, undergo gross changes, and one often notes inclusion bodies, or compacted masses of viruses or damaged cell organelles.
Most bacteriophages contain double stranded DNA, though single stranded DNA and RNA types exist as well. TRUE/FALSE
TRUE. The most widely studied bacteriophages are those of the intestinal bacterium E. coli, especially the ones known as the T even phages, such as T2 and T4.
An averaged sized E. coli cell can contain up to 200 new phage units at the end of this invasion period. Eventually, the host cell becomes so packed with viruses that it lyses, releasing mature virions. TRUE/FALSE
What is a temperate phage?
Special DNA phages, called temperate phages, undergo adsorption and penetration into the bacterial host but are not replicated or released immediately. Instead the viral DNA enters an inactive prophage state, during which it is inserted into the bacterial chromosome. It will be copied during normal cell division. This condition, in which the host chromosome carries bacteriophage DNA is termed "lysogeny"
What is induction?
Because viral particles are not always produced, the bacterial cells carrying temperate phages do not lyse, and they appear normal. In induction, the prophage in a lysogenic cell will be activated and progress directly into viral replication and the lytic cycle.
What is Lysogeny?
It is a less deadly form of parasitism than the full lytic cycle and is thought to be an advancement that allows the virus to spread without killing the host.
What is Lysogenic conversion?
Occasionally, phage genes in the bacterial chromosome cause the production of toxins or enzymes that cause pathology in the human. When a bacterium acquires a new trait from its temperate phage it is lysogenic conversion.
What is the relationship between lysogenic conversion and bacteria?
This phenomenon first discovered in the 50s, was discovered in the bacterium diphtheria, Corynebacterium diphtheria. The diptheria toxin responsible for the deadly nature of the disease is a bacteriophage product. Without the phage, this agent is harmless.
Vibrio cholerae and Clostridium botulinum are two other examples.
What are viral plaques?
The areas where virus infected cells have been destroyed show up as clear, well defined patches in the cell sheet. Plaques are essentially the macroscopic manifestation of cytopathic effects.
Among the known causative viruses in order of importance are...
rhinoviruses(which cause about 50% of colds), paramyxoviruses, enteroviruses, coronaviruses, reoviruses and adenoviruses.
List 2 diseases caused by viruses.
Creutzfeldt disease/Bovine spongiform encephalopathy(mad-cow).
What is a satellite virus?
These viruses are actually dependent on other viruses for replication.
Two examples are the adeno-associated virus, which can replicate only in cells infected with adenovirus, and the delta agent, a naked starnd of RNA that is expressed only in the presence of the hepatitis B virus and can worsen the severity of liver damage.
What is a viroid?
Plants are parasitized by virus like agents called viroids that differ from ordinary viruses by being very small(about one-tenth the size of an average virus), and being composed of only naked starnds of RNA, lacking a capsid of any other type of coating.