|
Easily Understand Viral Microbiology
1. Are viruses cellular beings?
Viruses are considered living beings but they do not have cellular structure.
There is some controversy regarding their classification as living beings. Their characteristics of self-reproduction and of having genetic material however reinforce that classification.
2. What is the basic structure of a virus?
Viruses are constituted of genetic material (DNA or RNA) covered by a protein capsule also known as a capsid. Some viruses, like HIV, have in addition an external envelope derived from the plasma membrane of the host cell from which it came.
Virus Review - Image Diversity: virus structure
3. Are there non-parasitic viruses?
All viruses are obligate intracellular parasites, i.e., they depend on the host cell to complete their life cycle. A virus does not have its own metabolism.
4. Why is it a strong evolutionary hypothesis that although viruses are the structurally simplest beings they were not the first living beings?
The fact that viruses are obligate intracellular parasites makes very weak the hypothesis that virus appeared before cellular beings in the evolution of life.
5. What is the genetic material of a virus? How does that material act in viral reproduction?
There are DNA viruses (double strand or single strand DNA) and RNA viruses (double strand or single strand RNA too). Viruses inoculate their DNA or RNA molecules into cells and these cells (by means of transcription or reverse transcription and translation) synthesize proteins for the assembling of a new virus. This synthesis is commanded by the viral DNA or RNA molecules.
6. What is the typical reproduction cycle of a DNA virus?
A typical virus has proteins on its capsid that bind to the outer membrane of the host cell. In the place where the virus adhered viral proteins act to break the cell membrane and then the virus injects its DNA molecules into the host cell.
Within the host cell the viral DNA is transcripted and thus messenger RNA is produced. Viral mRNA then is translated and viral proteins are made.
Viral polypeptides made within the host cell are cut by enzymes called proteases and then copies of the virus are assembled with the newly formed proteins. When the assemblage of new viruses is completed the cell membrane breaks and the viruses are released to the outside. One sole infected cell can produce hundreds of viruses.
Virus Review - Image Diversity: viral life cycle
7. What are retroviruses? How do they reproduce and what is the role of the enzyme reverse transcriptase?
Retroviruses are viruses whose genetic material is RNA. HIV and the virus of SARS (severe acute respiratory syndrome) are examples of retrovirus.
These viruses inoculate their RNA into the host cell and within the cell the viral RNA is reversely transcripted into DNA. DNA made from the viral RNA then commands the synthesis of viral proteins for the assemblage of new viruses and the breaking of the host cell to liberate them outside.
The enzyme reverse transcriptase is the catalyst of the reverse transcription of RNA into DNA. The enzyme is part of the virus and it is also inoculated into the host cell.
Virus Review - Image Diversity: retrovirus
8. What is the basic structure of the HIV virus? What is the function of the glycoproteins of its envelope?
HIV is an RNA virus. In its core there are two strands of RNA and reverse transcriptase molecules. The core is covered by a capsid, a layer of proteins. The capsid then is covered by an envelope having glycoproteins and lipids.
The glycoproteins of the HIV envelope are located on the outer surface of the virus and they are responsible for the recognition of the cells to be infected (the HIV host cell is the CD4 lymphocyte) and for the adhesion of the virus to the cell membrane. (CD4 is a receptor glycoprotein of the outer membrane of some lymphocytes).
Virus Review - Image Diversity: viral envelope
9. What are bacteriophages?
Bacteriophages are viruses specialized in parasitism of bacteria. They are used in genetic engineering as molecular cloning vehicles to insert recombinant DNA into bacteria. They were also used in the former Soviet Union to treat bacterial infections.
Bacteriophages have a polyhedron-like capsid and DNA as genetic material. The “head” of the virus is connected to a tail that ends in small fibers that help the virus to attach to the bacterial cell wall and to inject its genetic material into the host.
Virus Review - Image Diversity: bacteriophage
10. What is meant when it is said that a virus is in an inactive state?
Viruses considered in inactive state are those whose genetic material is within host cells without synthesis of viral proteins and assemblage of new virus. The life cycle of these viruses can be activated under certain conditions and then synthesis of viral proteins begins and new copies are made.
The virus that causes herpes (herpes virus) is an example of a virus that stays in an inactive state and is sometimes activated.
11. What are the main human diseases caused by virus?
Among diseases caused by virus are common cold, flu, mumps, variola (considered eradicated nowadays), rubella, measles, AIDS, the viral hepatitis, human papillomatosis (HPV infection), rabies, dengue fever, yellow fever, poliomyelitis (an almost eradicated disease in developed countries), hemorrhagic fever from Ebola virus, SARS (severe acute respiratory syndrome).
Viruses also cause many other diseases in animals and plants.
12. SARS is a disease that appeared in 2003 with epidemic features in the province of Guangdong, in east China. What type of agent causes SARS?
SARS is caused by a virus from the coronavirus group, a RNA virus (retrovirus). SARS can be fatal.
13. What is crystallization of a virus? What is the importance of this process?
Crystallization is the process of transformation of viral components into organized solid particles.
Crystallization of biological macromolecules, including viral components, is used to study structural characteristics, for example, through X-rays, laser beams, etc.
Virus Review - Image Diversity: viral crystallization
|
