Difference between revisions of "Virus"
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This infection cycle of replication has two forms, lysogenic and lytic. In the lysogenic a virus will implant its DNA in the host cell's and wait until the cell is under stress and then begin to copy more of itself. This method allows for the virus gene (called the pro-phage) to continue through multiple generations of cells until the correct replicating time has arrived. Viruses that use this cycle are said to be 'latent' and are often retroviruses (their genetic material is RNA, as opposed to DNA). An example of this type of virus would be the HIV virus. The other method (the lytic cycle) involves a virus directly injecting its genetic material into the cell and immediately forcing it to make viral copies. After about 200 viruses have been produced the cell lyses (explodes) and the copies are now free to infect more cells. Many of these viruses are bacteriophages. This is because bacterium have a cell wall that does not allow the absorption of the virus like the [[plasma membrane]] of animal cells do, forcing the virus to inject only its genetic material. | This infection cycle of replication has two forms, lysogenic and lytic. In the lysogenic a virus will implant its DNA in the host cell's and wait until the cell is under stress and then begin to copy more of itself. This method allows for the virus gene (called the pro-phage) to continue through multiple generations of cells until the correct replicating time has arrived. Viruses that use this cycle are said to be 'latent' and are often retroviruses (their genetic material is RNA, as opposed to DNA). An example of this type of virus would be the HIV virus. The other method (the lytic cycle) involves a virus directly injecting its genetic material into the cell and immediately forcing it to make viral copies. After about 200 viruses have been produced the cell lyses (explodes) and the copies are now free to infect more cells. Many of these viruses are bacteriophages. This is because bacterium have a cell wall that does not allow the absorption of the virus like the [[plasma membrane]] of animal cells do, forcing the virus to inject only its genetic material. | ||
| − | ==Are | + | ==Are viruses alive?== |
There is disagreement on whether or not viruses should be considered alive since they do not share many of the processes that other forms of life have. They do not feed, respire, grow, reproduce through cell division, or move under their own power. Viruses also do not have a cell structure, despite having genes. | There is disagreement on whether or not viruses should be considered alive since they do not share many of the processes that other forms of life have. They do not feed, respire, grow, reproduce through cell division, or move under their own power. Viruses also do not have a cell structure, despite having genes. | ||
Revision as of 00:53, August 19, 2008
A virus is a microscopic, non-cellular, infectious agent that has two characteristics: It has genetic material (either DNA or RNA) inside a protective protein coat.[1]
Method of replication
To reproduce itself, a virus needs to infect a living cell. The genetic material is inserted into the cell, and the reproductive machinery of that cell is then effectively "hijacked": the cell starts to produce components of new virus particles. These components spontaneously self-assemble and the new virus particles can then infect other cells, where the same process happens.
Forms of replication
This infection cycle of replication has two forms, lysogenic and lytic. In the lysogenic a virus will implant its DNA in the host cell's and wait until the cell is under stress and then begin to copy more of itself. This method allows for the virus gene (called the pro-phage) to continue through multiple generations of cells until the correct replicating time has arrived. Viruses that use this cycle are said to be 'latent' and are often retroviruses (their genetic material is RNA, as opposed to DNA). An example of this type of virus would be the HIV virus. The other method (the lytic cycle) involves a virus directly injecting its genetic material into the cell and immediately forcing it to make viral copies. After about 200 viruses have been produced the cell lyses (explodes) and the copies are now free to infect more cells. Many of these viruses are bacteriophages. This is because bacterium have a cell wall that does not allow the absorption of the virus like the plasma membrane of animal cells do, forcing the virus to inject only its genetic material.
Are viruses alive?
There is disagreement on whether or not viruses should be considered alive since they do not share many of the processes that other forms of life have. They do not feed, respire, grow, reproduce through cell division, or move under their own power. Viruses also do not have a cell structure, despite having genes.
Examples
Examples of viruses include the influenza virus, the common cold, HIV, smallpox and polio.
Immunities
Viruses are not targeted by antibiotics, the drugs used to kill bacteria, and so use of antibiotics for viral infections is usually inappropriate.
References
- ↑ Wile, Dr. Jay L. Exploring Creation With Biology. Apologia Educational Ministries, Inc. 1998