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Biology 103
2001 Second Web Report
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Getting at the Root of the Problem: Genetic Disease and the Human Genome Project

Jennifer Trowbridge

Disease is a broad problem that as living beings, humans inevitably encounter. While many of these diseases result solely from an individual's surrounding environment, there are numerous others which are mainly the outcome of genetics. Recent advances in medical technology suggest that genetically based diseases could, in the future, be cured by human manipulation of the genes themselves. The exact procedures for this process have not yet been discovered, but the first step lies in a national and international genetics project that has been named the Human Genome Project (HGP). The completion of the HGP will provide a base upon which other extensive genetic research can build, including the curing of genetically based diseases. For this reason, the Human Genome Project itself will be explained first and it's relevance to disease control afterward.

The Human Genome Project officially began in 1990 due to the joint efforts of the U.S. Department of Energy and the National Institutes for Health. (2). A genome is the all the DNA in an organism, thus including genes and chromosomes. Genes carry recipes for proteins, which in turn determine a person's physical features, his or her metabolism, ability to fight infection, and sometimes behavior. The HGP seeks to, first, record every gene in the human body, and secondly, to disclose the sequences of the estimated 3 billion base pairs in human DNA. (2) Furthermore, the project will give attention to ethical, legal, and social issues (ELSI), which directly points to its willingness to address, not avoid, these debatable topics.

The strict science that lies at the base of the Human Genome Project is both interesting and critically important to it's mission. The entire human genome is contained in each cell, with the exception of only mature red blood cells. (3)The ultimate determinate of the genome is the DNA, which is contained in the nucleus of the cell. It is a double helix, or ladder shape, where the sides are made sugar and phosphates and the rungs are nitrogen base pairs.

Adenine, Guanine, Cytosine, and Thymine are the only nitrogen base pairs for DNA strands. Nucleotides are one "unit" on a DNA strand; one sugar, one phosphate, and one nitrogenous base. The order of the four bases is the recipe that decides which proteins should be made, earlier referred to as DNA sequencing. Nitrogen bases on one side of the helix must match with the appropriate bases on the opposite side. Cytosine (C) pairs with Guanine (G), and Thymine (T) with Adenine (A). When chromosomes, X-shaped bodies within the cell that contain DNA, are stained and viewed under microscope, nitrogen base pairs can be clearly identified. (3)

In order for DNA sequences to make proteins, they must first "unzip" themselves into two strands. Messenger RNA (mRNA) is then formed when Thymine is replaced by Uracil (U). mRNA leaves the nucleus of the cell, then slides through an organelle known as the ribosome like a train pulling through a train station. The codons, or triplets of nitrogen bases on one side of the RNA strand, attract specific polypeptides while moving through the ribosome. These polypeptides then bond to form a chain based on the instructions given by the nitrogen base sequences. This chain is a protein, which when complete, performs precise and vital functions in the cell.

Because the human genome contains approximately 3 billion base pairs, it is clearly a challenge to record every sequence. Furthermore, 1.4 million locations have been found where the difference of one base pair in the DNA sequence changes the outcome of the final protein. The progress of the Human Genome Project has been quicker than expected however, and a rough draft of genome has recently been completed.

While the genome and protein making process is fairly well understood, the exact functions of proteins in cells is not. It is especially unclear as to how proteins made from defective genes eventually translate into disease symptoms. The Center for Disease Control explains that "a wide gap exists between sequencing and discovering genes and the safe and effective use of genetic information to prevent disease and improve health."  (4) Although the gap may exist now, it is one that scientists are working hard to fill, because it could mean a breakthrough in medicinal science that would forever change the way genetic diseases are treated.

Currently, 15 - 60 in every 1,000 infants are born with congenital disorders. Many of these diseases are severe and can be deadly. Others that seem less harmful can cause problems later in life, such as heart disease or hypertension. (1)These genetically based diseases can often be identified by examining DNA sequencing. Down syndrome, for example, is caused by a third copy of the twenty-first chromosome. Other genetic diseases include hemophilia, sickle cell anemia, neurofibromatosis, some forms of cancer, and cystic fibrosis.

Cystic fibrosis appears to be caused by harmful alteration in nucleotide sequence. It occurs most often in people of European descent. The gene malformations, the most common of which is DeltaAF508, are recessive. Both parents must therefore be carriers and pass along their recessive genes for a child to be diagnosed. The symptoms and effects of cystic fibrosis include a thickening of mucus in the lungs which results in fluid retention and lung infection, which can in turn lead to chronic lung disease and pancreatic insufficiency. (5)(6)A few cystic fibrosis patients do not live past ten years, though the average life expectancy is between 30 and 50 years old.

It is easy to see the wide gap between our knowledge of the gene function of and bodily response to cystic fibrosis. Moreover, it is hard to know how to fix the problem because the role of proteins is not very well understood. There has been evidence that proteins can change functions depending on their environments, which only complicates the issue. The most obvious action at this point is to treat symptoms of cystic fibrosis because we cannot yet change the root of the disease. In an attempt to actually go after the genes, however, the American Society of Human Genetics on Cystic Fibrosis explains that "intense efforts also are underway to develop gene therapy strategies to deliver the normal CF gene to the respiratory tract." (5)Regardless of the success of this treatment, the Human Genome Project will provide valuable information that will allow diseases like cystic fibrosis to be better studied and understood. Hopefully it will provide enough of a lead that cystic fibrosis can eventually be stopped where it begins: in the genes.

While the Human Genome Project and its possible future effect on genetic disease reflects true scientific progress, it is not such a straightforward topic. Some feel that hampering with genes is stepping out of our role as humans and creatures in nature. There are also those who fear the misuse of gene alteration. For example, a parent could "design" her or his child's looks and other genetic makeup before birth. These are the types of issues that arise when the ethic, legal, and social issues are addressed. They are valid and important issues to deal with in considering support for gene research. Nevertheless, if used correctly, information obtained by the Human Genome Project could provide a cure for painful and life shortening genetic diseases.

WWW Sources

1)World Health Organization, Human Genetics

2)U.S. Department of Energy, Human Genome Project Information

3)U.S. Department of Energy,The Science Behind the Human Genome Project

4)Center for Disease Control, Gene Sequencing and Discovery are only the Beginning

5)Federation for American Societies for Experimental Biology, Cysitc Fibrosis Carrier Screening

6)The Pharmeceutical Industry, Implications of success of the Human Genome Project

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