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Cystic fibrosis is a debilitating disease facing many people today. At the present time there is no cure available. According to the cystic fibrosis foundation of America, cystic fibrosis can be traced back as early as 1595. The first documented case was not reported until 1936.
One group of people that seem to be affected the most by cystic fibrosis is Caucasians. Recent statistics indicate that 1 in 3, 200 live caucasian births are afflicted with cystic fibrosis. For reasons that are currently unknown African Americans have a slightly lower chance of developing cystic fibrosis usually 1 in 15, 000 live births. Cystic fibrosis remains to be a rare disease in the asian population as well as the native American population. In the United States there are 1, 000 children born each year with cystic fibrosis. Current numbers suggest that there is over 30, 000 people in the United States alone living with this crippling disease.
In the United states approximately 1 in 25 - 30 people are carriers of the mutated gene that causes cystic fibrosis (Sheppard and Nicholson). The cystic fibrosis foundation of America has reported that there is over 10 million people who are possible carriers of the mutated gene. Cystic fibrosis is an inherited genetic disease. In actuality cystic fibrosis is an autosomal recessive disease (Lim and Zeitlin). Cystic fibrosis is now considered the most common genetic disease among Caucasians (Sheppard Nichsoln). Although cystic fibrous tends to display an ethnicity bias it does not have a gender bias.
The autosomal recessive disease indicates that the mutated gene that causes cystic fibrosis is not located on the sex chromosome. In 1989 the mutated gene that causes cystic fibrosis was discovered, and this was one step closer to understanding a disease that affects so many people (Sheppard and Nicholson). The mutated gene is located on autosomal chromosome number 7. The mutation occurs in the cystic fibrosis transmembrane conductance regulator gene (CFTR). At the present time researchers have concluded that there are over 900 different mutations in the CFTR gene (Sheppard Nicholson). The severity of the disease is based upon the variations of mutations that are expressed (Panes ear).
For instance a gene with over 900 mutations can wreak havoc on the human body causing a plethora of problems. When a person is a carrier of the mutated CFTR gene, and is paired with a non-carrier the cystic fibrosis phenotype will not be expresses. This is due to the recessive characteristics of the disease. Cystic fibrosis will be expressed if both parents are carriers for the mutated gene. The composition and the functionality of what the CFTR has been a continuous battle until recently. The CFTR protein is a chloride ion channel (Mcauley and Elborn).
The CFTR protein is composed of two transmembrane spanning domains with two nucleotide-binding domains called NBD 1 and NB 2, and a regulatory domain (R) (Panesar). The regulatory or R domain contains multiple target phosphorylation sites for protein kinase A and C (Harris and Argent). The CFTR channel is regulated by cyclic adenosine 3, 5 - monophosphate (camp) (Pansear). Once the regulatory domain has become phosphorylated, ATP hydrolysis at the NBF domains is essential to keeping the channel open (Harris and Argent). Panesar describes the mechanics of the functioning CFTR protein as follows: chloride ions enter the cell against an electrochemical gradient coupled to sodium by the sodium- potassium chloride ion co ransomer.
The chloride ion then exits from the surface via a channel down the gradient, which is regulated, by camp. The complete functioning of and mechanics of the CFTR still remain a mystery. The mutations that can occur in the CFTR are broken down into five classes. Class I mutations are characterized by the total absence of the CFTR.
Class II are believed to be associated with possible defects in the trafficking and folding of the CFTR. Class III is found to be responsible for the abnormal regulation of chloride conduction in fully processed CFTR. Class IV mutations have been linked with decreased chloride conduction in fully processed CFTR. Many aspects of the functioning of class V mutation are not completely understood presently, but ther are believed to be associated with CFTR synthesis (Lim and Zeitlin). Class I defects of the CFTR mutations are the result of a premature stop codon which is believed to actively interfere with translation of the CFTR (lim and Zeitlin).
The most common mutation that is expressed in cystic fibrosis and seen in over 70 % of people is a class II mutation called delta 508 (Lim zeitlin). The delta 508 mutation is abase triplet mutation. This mutation actually deletes the phenylalanine residue at amino acid 508 of the CFTR protein (Mcauley and Elborn). The delta 508 mutation is generally seen in populations of northern European decent (Pansear).
The loss of the phenylalanine residue lies within the first nucleotide binding factor region of the protein (Harris and Argent). In this mutation the protein becomes mi localized within the cell, and remains in the endoplasmic reticulum (er) rather than being transported through the intracellular member ane. One current theory sugeststhat the trafficking problem might originate from the folding of the protein. This particular mutation is responsible for the mis folding, and therefore causes the protein to be rejected from sorting and processing (Harris and Argent). Class III mutations are able to function and undergo normal trafficking to the plasma membrane, but are not able to be stimulated by camp. Class IV mutations are generally denoted by an abnormally low chloride conductance in the apical plasma membrane.
Which is unable to be regulated by cAMP. The concentration of the chloride conductance plays a very important role in this mutation. The mechanism by which epithelia secrete electrolytes is essential to this mechanism. The electrolytes that are typically secreted are Nacl, Na Hco 3, and water.
In the event the fluid secreted is drastically reduced or inhibited the surface of the epithelia begin to dehydrate. The dehydration of the epithelia will eventually lead to an accumulation od secretions such as mucus. (Harris and Argent). Class V mutations tend to be a little milder then the other classes of u tations. These are the least common mutations found within the CFTR gene, and are therefore the least symptomatic. This mutation can be briefly characterized by a reduction in the number of normal CFTR proteins, and possibly a reduction in chloride ion transport (Lin and Zeitlin).
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Research essay sample on Cystic Fibrosis Autosomal Recessive
