Untitled Page

he Human Genome Project involves mapping human DNA, our biological coding (National Geographic News, 2006). To do this, geneticists separate DNA molecules, duplicate them, and read the molecules. The reading is rigorous work, and can be done many different ways. First, scientists heat the DNA double helix at about 90* Celsius, in water, making two single strands. Dr. Belouchi states that each nucleotide is composed of one phosphate molecule, one ribose molecule, and a base molecule: either Adenine (A), Cytosine (C) Thymine (T), and Guanine (G) (M. Belouchi, personal communication, March 29, 2007). Next, they must get rid of the terminal phosphate at one end of the DNA strand. They do this by using an enzyme, called phosphatase, to cleave the phosphate.

hey must then place the DNA in a test tube, add a radioactive phosphate, called P32, and add and an enzyme kinase. Kinase, works like a nanomachine, attaching P32 to the end of the DNA. Next, copies of the DNA are made, and placed into 4 different tubes, each containing different chemicals. Each type of chemical will cut the DNA in different areas. Chemical 1 will sever the DNA after some of the A nucleotides. Chemical B will cut after some of the A or G nucleotides. Chemical 3 will cut after some of the T or C nucleotides, and the final chemical will sever the DNA following some of the T nucleotides. This chemical digestion only partially cuts the DNA, skipping some bases, leaving some DNA intact. This allows for DNA with a base sequence of AACGT to be cut at various nucleotides of the same family.

NA is eventually cut at all possible places, giving many different sized strands. Sometimes, chemical 1skips an A, cleaving after the next one, intentionally. It is at this stage that the biochemists may start sequencing. The strands of DNA are placed in electrophoresis gel. This gel has a Jell-O-like texture. A negative charge is put at one end of the well of the machine, while a positive charge is put into the other end of the well. The stands slowly move from the negative to positive charge. As they enter the gel, the pieces move at different speeds, depending on their size (the smaller, the faster). For smaller DNA strands, or for better resolution, one may use a polyacrylamide gel.

hen the strands are at different positions in the gel, the charges are removed, halting the DNA’s movement. The gel is then removed, and placed on clear plastic. It is then wrapped in saran wrap, and covered by an unused X-ray film. The ensemble is placed in an X-ray reading cassette, developed and then read in a dark room. The radioactive elements can be seen as lines on the X-ray, in each of the four columns. By deduction, one can identify in what order the bases appear. If two lines appear four, and eight spaces up in the first well, this means that the original strand tested had A bases at positions four and eight in the molecule. By going through this slow process, one may determine the sequence of nucleotides in a gene.

here are, however, 30000 genes in the human genome. After 1977, many fast and efficient techniques were used to extract and read DNA (Genomics, 1999).These became automated, and began to show genes causing certain diseases in humans and other organisms. In 1995, the first complete DNA base sequence of an entire organism was produced by Crig Venter from the Institute for Genomic Research. Many complete genomes of micro organisms have been sequenced (Suzuki S. & Knudtson P, 1988). Dr. Belouchi states that newer technology results in each DNA base being coloured in a specific tone, allowing for rapid and massive gene sequencing (M. Belouchi, personal communication, March 29, 2007). Instead of taking 9 months to sequence a gene, a DNA analyzing machine, costing 500,000 dollars, can sequence an entire gene in merely 2 and a half hours.

his machine uses nanotechnology and capillary electrophoresis to determine the base sequences. A light source creates a different reaction in each of the four nucleotides, allowing each one to be identified as it reaches the end of the thin electrophoretic wire. This wire replaces the agarose gel used in traditional techniques. Scientists can compare an individual’s DNA to the healthy human genome, detecting any mutations. SNPs are not always dangerous, and can be caused by the inheritance of traits from both parents. Three nucleotides are called a codon. Each codon represents one amino acid. In cystic fibrosis, one mutated amino acid can result in a whole host of complications and increase mortality rate. Some simple diseases are caused by one genetic mutation, while others, such as asthma and cancer, are caused by multiple mutations. This process allows scientists to recognize diseases at early or non-existent stages. The information retrieved is then stored in a public library. A company called 454 life came out with new reading techniques (National Geographic News, 2006). Now, DNA strands pass through a very small machine called a nanopore. This machine uses nanotechnology to read the bases of the DNA strands and could allow geneticists to read an entire human genome in just a few hours. This method, however, is still being perfected (H. Sleiman, personal communication, March 29, 2007).