BIOLOGY PRESENTATION REPORT PAPER => Forumda Tartış

1.Introduction:

The report’s topic is the prion diseases. In the report, firstly the structure of prion protein will be explained, and then the progress of prion protein’s entrance to the cell will be summarized. After the brief summary of the spread of prion protein among cells, most common prion diseases will be introduced. CJD (Creautzfeld-Jakop disease), and BSE ( Bovine Spongiform Encephalopathy) will be determined much more deeply then the others. These disease’s spread over the world and Turkey will be explained, and finally the protection ways from these diseases will be given.
2. Prion protein:
2.1.What is Prion? :
The current definition of prion is the proteinaceus infectious particle that lacks nucleic acid. These infectious particles causes diseases such as Scrapie, BSE, CJD and mad-cow disease. This prion protein has two different structures.
2.2.The Prion Protein Structure:
In one of these structures, the protein carries out its normal cellular functions. The name of this normal protein is PrPc. PrPc is a cell-surface glycoprotein. This protein is most highly found on the nerve or brain cells. The functions of this protein is still not known properly; but it is thought that this protein is used in binding copper.
On the other hand, this protein can be converted into another form by genetic mutations or environmental factors. In this case this protein is a pathogenic protein and causes many diseases including Scrapie, BSE, and CJD. The name of this second protein structure is PrPcs.The natural effects and genetic influences can convert PrPc to PrPcs. Also PrPcs can act as a template on which PrPc is folded into the PrPcs protein. According to the authorities, a protein that is called as protein X may facilitate this process.











2.3.The Genetic Influence on Prion Disease:
Prion diseases are both genetic and transmissible. It is genetic because, the point mutations on PrP gene is genetically linked to the development of the familial development of prion diseases. The genetic mutations occurred on the gene cause the resulting protein be more likely to form pathogenic protein. This pathogenic protein converts other normal proteins to the pathogenic ones, and prion diseases occur. It is transmissible, because when the pathogenic protein is introduced to a normal individual’s brain, the same reaction will be processed. As a result, the prion diseases are both genetic and transmissible.me reaction

3. Prion Progress Within The Cell and The Body:

3.1. Prion Progress Within The Cell

Firstly, PrPc RNA is produced in the nucleus of the cell. This produced RNA then passes to ribosomes found on the Rough Endoplasmic-Reticulum. On these ribosomes, PrPc protein is formed from the PrPc RNA like any other protein. PrPc protein then passes to the golgi body and on the golgi body the proteins are put in vesicles. In these vesicles, PrPc protein is transported to the cell membrane. At the cell membrane PrPc meets with the infectious prion protein(PrPsc). PrPsc forces PrPc to change shape; to fold. These changes occur using old PrPsc as a template and result in the formation of new PrPsc proteins.Then these new infectious prions are put again in vesicles and start travelling around the cell. The new PrPsc containing vesicles may attach to the golgi bodies on which healthy prions are made at that moment. Therefore infectious prions start to become dominant in the cell.
Although both PrPsc and Prpc are made up of the same chemicals, the difference in their shapes is what makes PrPsc harmful and the PrPc harmless.
Prions may enter the brain the brain along the axons of the neurons as well as using immune cells to enter the blood.


3.2. Prion Progress Within The Body

Firstly, cows get infected from the prion and the infection spreads from one cow to another by feeding healthy cows with BSE infected cows. Prions reach humans by eating contaminated meat and in humans prion reach first to the gut. Prion is then taken by lymphocytes to the lymphoid tissues, like spleen. Spleen is the place where prion replication takes place mostly. Nerves which supply food or oxygen to the lymphoid tissues are responsible for taking the prion to the brain. In addition to this; since normally lymphocytes carry prions, prions may be taken to the brain by blood too.


5.WHAT'S BSE?

Mad cow disease, or bovine spongiform encephalopathy (BSE), is a fatal brain disorder that occurs in cattle and is caused by pathogenic prion protein. In BSE, the pathogenic protein causes the cow's brain cells to die, forming sponge-like holes in the brain. The cow behaves strangely and eventually dies.


5.1. Origins of BSE

BSE is thought to have come from a similar disease in sheep called scrapie. In the 1980s, producers of cattle feed (which often included ground meat and bone meal by-products from sheep) changed the way they processed feed. The change somehow allowed the scrapie disease agent to survive the cattle feed production process. Thus, contaminated food was fed to cattle, which then came down with BSE. At the time, neither scrapie nor BSE were thought to affect humans. So, meat (nervous tissue) from BSE-infected cows made it into the food supply. Humans who ate the infected meat (probably hamburger or other processed meats) contracted the BSE-causing agent and developed nvCJD.


5.2. How BSE Works
BSE is spread by contact with brain or other nervous-system tissue from an infected individual. Contact can be from eating food or food by-products that have been contaminated with nervous tissue, or from instruments that have contacted diseased nervous tissue. Once the infectious agent enters the brain, it can lie dormant for several years (even as long as 10 to 15 years). When activated, the agent kills brain cells, leaving large areas of spongy holes. Also, large clumps of abnormal prion proteins (plaques) are found in brain cells. Once the agent is activated, the disease runs its course in less than one year, and ultimately results in death.

5.3.Animal Consequences:
Cows infected with BSE:
1- lose weight,
2-show abnormal behavior (skittishness),
3-may become paralyzed and die.



5.4.Tests for BSE
To test for BSE, brain tissue from a suspected animal is injected into an experimental animal. Scientists then observe the experimental animal for signs of BSE. With the advent of the prion hypothesis, molecular tests are being developed to detect abnormal prions in suspected animals. One company, Prionics Inc., has marketed diagnostic tests for BSE.

6.WHAT IS nvCJD?
nvCJD (variant Creutzfeldt-Jacob Desease) is a prion related disease, which is one of the TSE (Transmissible Spongiform Encephalopathies) that are fatal, causing irreversible cumulative brain damage. nvCJD typically occurs a decade later and it has cerebral involvement so dementia is more common and patient seldom survives a year (originally thought to be sporadic, but now
known to be familial as well).

6.1. Symptoms:
At first the patients usually experince psychiatric symptoms, which most commonly take the form of depression or less often a schizophrenia-like psychosis. There are also some unusual sensory symptoms such as “stickiness” of the skin experienced by half of the cases. Other symptoms of the disease are unsteadiness, loss of motor control, difficulty walking and involuntary movements, which then make the patient completely immobile and mute and eventually cause death.
6.2. Historical Development and nvCJD Today
nvCJD was first reported in March 1996 in the UK and most patients have a history in the UK. At present it is known that there are 87 people who have died or are dying from nvCJD. The disease can only be confirmed by the pathological examination of the brainThere is no cure of this disease yet.

6.3. Differences Between CJD and nvCJD
Firstly, nvCJD is associated to BSE unlike CJD. Then, young people are most affected with an average of death under 30 years.vCJD(it affects people between the ages 15 and 59. Another difference is that it takes longer to kill(almost two years) in nvCJD unlike CJD. Finally, nvCJD involves psychiatric features as hallucinations.
8. PROTECTION FROM PRION DISEASES:

8.1.Spacies barrier for prion related diseases:

Until 1986, it was thought that prion diseases can’t pass from one species to another. But in 1986 the disease called “madcow” changed this taboo. In 1980’s the disease passed to cows from their feeds. And this passing events continued tragically. From cows to people and then to cats. Even some deer at zoos got infected. This situation enlarged the danger. And people started to search if there is species barrier for prion or not.
Madcow disease was constructed inside the sheep, cows, mousses, goats and monkeys experimentally. At laboratories, the scientists studied to construct pig prions but this process was difficult if we compare with other species. They also tried to construct prions inside chickens but they couldn’t. By means of these kinds of researches the species barrier for prion diseases became more clear. Here is the results:
• It is a little bit difficult to pass from pigs to mousses
• It is possible to pass from deer to mousses
• It is possible to pass from feeds to cats
• It is possible to pass from foods to humans
• It is possible to pass from monkeys to mousses
• It is possible to pass from goats to mousses
• It is impossible to pass from sheep to humans
• It is impossible for dogs to get infected
The results show the fact that fishes, chickens and rabbits are completely safe. The scientists think that it is related with genetic codes of species. So the genetic sequences of some animals have tendency to get prion diseases as others don’t have.



8.2.Protection Ways For BSE:
First of all we must know that there is no medical treatment for prion related diseases. That means they are all fatal. So we must be so careful about them. There are some advises to stay away from that kind of diseases for humans. Here is the things that we must consider for our health:
1. Sausages mustn’t be consumed so much.
2. Especially hamburgers and this kind of fast foods mustn’t be eaten so much.
3. We must buy our meats from trustworthy sellers
4. We must consume more vegetables or fruits instead of meats. These kinds of foods have no risks
5. The meats that are not controlled by the government mustn’t be consumed.
6. Exporting processes must be conducted carefully. The source countries of BSE are known. Exportation from these countries must be limited.
7. We must consume more sheep products instead of cows. Because there is a species barrier between sheep and human for prion related diseases.
8. Chickens, rabbits and fishes are completely safe.
9. The most dangerous parts of the infected animals are brains, intestines and spinal cords. The best way is to avoid to consume these parts.
10. It is still being searched if the disease passes by blood transfusion or not. But we must consider the possibility and be careful.
11. We must follow the news about madcow. Since it is a new topic for scientists, there are still some unclear parts of the topic. The more information about prion is gathered the more the protection methods become clear.
REFERENCES: FOCUS (TO DISCOVER AND UNDERSTAND THEWORLD) , SAYI:2001, 3 MART 2001,YIL:7

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