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Credits:

http://www.slic2.wsu.edu:82/hurlbert/micro101/pages/Chap11.html

http://www.ornl.gov/sci/techresources/Human_Genome/medicine/genetherapy.shtml

http://www.livescience.com/viruses/

http://www.vitagen.com.sg/livin.htm

http://www.virology.ws/2009/10/19/ten-cool-facts-about-viruses/

http://www.netdoctor.co.uk/health_advice/examinations/bloodsamples.htm


http://www.webmd.com/hiv-aids/human-immunodeficiency-virus-hiv-test

http://www.poultry-health.com/library/serodiss/haemaggl.htm

http://www.bdbiosciences.com/support/resources/baculovirus/plaque_assay.jsp

http://education.yahoo.com/reference/dictionary/entry/polymerase%20chain%20reaction





HIV - VIRUS


A virus is defined as any of a various number of submicroscopic parasites that can infect any animal, plant or bacteria and often lead to very serious or even deadly diseases. A virus consists of a core of RNA or DNA, generally surrounded by a protein, lipid or glycoprotein coat, or some combination of the three. No virus can replicate without the help of a host cell, and though they can be spread, viruses lack the ability of self-reproduction and are not always considered to be living organisms in the regular sense.

Some of the most common or best known viruses include the human immunodeficiency virus (HIV), which is the virus that causes AIDS, the herpes simplex virus, which causes cold sores, smallpox, multiple sclerosis, and the human papilloma virus, now believed to be a leading cause of cervical cancer in adult women. The common human cold is also caused by a virus.




- TYPES OF VIRUSES -

Structure

  • Helical

These viruses are composed of a single type of capsomer stacked around a central axis to form a helical structure, which may have a central cavity, or hollow tube. This arrangement results in rod-shaped or filamentous virions: these can be short and highly rigid, or long and very flexible. The genetic material, generally single-stranded RNA, but ssDNA in some cases, is bound into the protein helix by interactions between the negatively charged nucleic acid and positive charges on the protein. Overall, the length of a helical capsid is related to the length of the nucleic acid contained within it and the diameter is dependent on the size and arrangement of capsomers. The well-studied Tobacco mosaic virus is an example of a helical virus.
  • Icosahedral

Most animal viruses are icosahedral or near-spherical with icosahedral symmetry. A regular icosahedron is the optimum way of forming a closed shell from identical sub-units. The minimum number of identical capsomers required is twelve, each composed of five identical sub-units. Many viruses, such as rotavirus, have more than twelve capsomers and appear spherical but they retain this symmetry. Capsomers at the apices are surrounded by five other capsomers and are called pentons. Capsomers on the triangular faces are surround by six others and are call hexons.



  • Enveloped virus

Some species of virus envelope themselves in a modified form of one of the cell membranes, either the outer membrane surrounding an infected host cell, or internal membranes such as nuclear membrane or endoplasmic reticulum, thus gaining an outer lipid bilayer known as a viral envelope. This membrane is studded with proteins coded for by the viral genome and host genome; the lipid membrane itself and any carbohydrates present originate entirely from the host. The influenza virus and HIV use this strategy. Most enveloped viruses are dependent on the envelope for their infectivity.




These viruses possess a capsid that is neither purely helical, nor purely icosahedral, and that may possess extra structures such as protein tails or a complex outer wall. Some bacteriophages, such as Enterobacteria phage T4 have a complex structure consisting of an icosahedral head bound to a helical tail, which may have a hexagonal base plate with protruding protein tail fibers. The tail structure acts like a molecular syringe, attaching to the bacteria host and then injecting the viral genome into the cell.



Bad Viruses
Prions

Some neurological diseases are caused by protein infectious particles (PRIONS). These include several animal and at least 3 human diseases. One of these diseases, KURU, infects its victims when they eat the brain tissue of their enemies (a questionable activity at best). The best studied of these diseases is scrapies in sheep. The disease entity seems to be composed completely of PROTEIN and to entirely lack any nucleic acid. This poses a major problem given the significant role of DNA and RNA in life. Three theories are currently being considered to explain prions.

Those prions contain as yet undetected nucleic acid. Extensive purification and testing using the most sensitive methods available have failed to demonstrate any nucleic acid in purified, infectious prions.
That an unknown bacterium that is hard to cultivate and that passes through filters is responsible. Again, there is no proof for such an organism.

Those prions represent a type of protein that is able to convert a "normal" protein into a "prion protein". This theory is currently the most popular and there is some evidence accumulating to suggest that it is valid. This theory says that when the prion protein gets into the brain of a victim it binds to a normal or pre-prion protein and somehow converts it into a prion; the new-prion then proceeds to convert other natural proteins. As the number of prions increase destruction of the brain occurs, eventually killing the victim.



ARE THERE PRIONS IN OUR FUTURE?

This is a case of an Emerging Disease about which we understand too little to know whether to be scared-out-of-our-wits or just to be wary and concerned. The Press/TV/Tabloids find prions a good way to sell their services and they tend to hype it up for that purpose. However, there are scientists who are very concerned about the potential dangers of prions. The following are some points of information (tentative) to keep in mind:

  1. There is still some serious debate within the scientific community as to the existence of prions and their role in diseases like the Mad Cow Disease.
  2. Currently the preponderance of data support the idea of prions being "killer proteins".
  3. Prions are very tough; they are not destroyed by autoclaving, cooking temperatures, most disinfectants or being buried in the soil for months.
  4. They are slow acting, however there was a recent death in a young person after exposure only a couple of years previously.
  5. No cases of Mad Cow Disease disease (in cattle) have been reported in the US, but Mad Cow-like diseases infect deer and elk in the US.
  6. There is no treatment for prion diseases; it is a death sentence.
  7. Prevention is uncertain. In UK they have killed and burned a significant percentage of the cattle. British beef can not be imported into most countries.
  8. The disease seems to be spread by animals eating the remains of other animals, particularly of closely related species. However, it also seems to be spread by other means, yet unknown.
  9. Feeding of animal parts to cattle and sheep is in the process of being banned in the US.




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