Genetic Engineering and Biotechnology - More Applications Of Genetic Research
dna nanotechnology identify disease
Most applications of genetic biotechnology are scientific, agricultural, and medical. However, geneticists are also engaged in product research and development of related technology and in legal determinations. Involvement with legal matters and the criminal justice system often takes the form of DNA profiling, also known as DNA fingerprinting. Since every organism has its own unique DNA, genetic testing can definitively determine whether individuals are related to one another and whether DNA evidence at a crime scene belongs to a suspect. It can also accurately identify a specific strain of a bacterium.
One example of researchers' use of genetic profiling to identify disease-causing bacteria was reported by Rex Dalton in "Genetic Sleuths Rush to Identify Anthrax Strains in Mail Attacks" (Nature, vol. 413, no. 6,857, October 18, 2001). Dalton described how the anthrax attacks throughout the United States during the first weeks of October 2001 spurred researchers to work quickly to identify the strains of bacteria involved. The researchers hoped to help identify the origin of the anthrax spores and presumably trace them to their source. Geneticist Paul Keim at Northern Arizona University in Flagstaff led the research that used amplified fragment length polymorphism DNA analysis and another test called multilocus variable-number tandem repeat (VNTR) analysis (used with microorganisms to examine the Bacillus anthraces).
Dalton wrote that it took Keim's research team about twelve hours to analyze a single sample. While several samples were ultimately determined to have been derived from the virulent "Ames strain," it was not a simple task to trace the Ames strain to a single source because it has been passed around the world by researchers. It had been commonly used in laboratory research to develop vaccines and tests after its original isolate was removed from a dead animal in the 1950s near Ames, Iowa.
The Merck Manual of Diagnosis and Therapy (17th edition, Merck & Co., Inc., 1999–2003, http://www.merck.com/mrkshared/mmanual/home.jsp) describes forensic genetics as using molecular genetic techniques to identify an individual's genetic makeup. Forensic genetics relies on the measurement of many different genetic markers, each of which normally varies from individual to individual, and may be used to determine whether two people are genetically related. For example, since half of a person's genetic markers come from the father and half from the mother, analyses of these DNA markers enable laboratory technologists to establish that one person is the offspring of another. Analysis of DNA derived from blood samples can determine whether the supposed parents of a particular child are actually the biological parents. DNA markers may also be used to identify a specimen and establish its origin—that is, definitively determine the individual from whom it came. Biopsies, pathologic specimens, blood, and semen samples can all be used to measure DNA markers.
Forensic investigations often involve analyses of evidence left at a crime scene such as trace amounts of blood, a single hair, or skin cells. Using the polymerase chain reaction (PCR), DNA from a single cell can be amplified to provide a sample quantity that is large enough to determine the source of the DNA. In PCR the double strand of DNA is denatured into single strands, which are placed in a medium with the chemicals needed for DNA replication. The single strands both become double strands, yielding twice the amount of the initial DNA sample. The double strands are once again denatured to form single strands, and the process is repeated until there is a sufficient quantity of DNA for analysis. Analysis is usually performed using gel electrophoresis, in which DNA is loaded onto a gel and an electrical current is passed through the DNA. Investigators are then able to observe larger molecules migrating more slowly than smaller ones. Examining VNTRs (variable-number tandem repeats) is a procedure that identifies the length of tandem repeats in an individual's DNA. VNTR is an especially useful technique in forensic genetics, because when it is performed in careful lab conditions the probability of two individuals having the exact same VNTR results is less than one in a million.
DNA evidence is preferred by forensic specialists because, while fingerprints can often be erased or eliminated and hair color and appearance may be altered, DNA is immutable. It can be used to identify individuals with extremely high probability and is more stable than other biological samples such as proteins or blood groups. Forensic genetics can be a powerful tool and has been used successfully to eliminate suspects and clear their names. Though not as useful in proving guilt, it provides solid and often convincing evidence when many alleles match.
The first admission of DNA evidence in criminal court occurred in 1987, when the State of Florida used it as part of the prosecution case to convict a suspect of a series of sexual assaults (Florida v. Tommy Lee Andrews). In 1989 the Federal Bureau of Investigation (FBI) began accepting work from state forensic laboratories, and a 1996 National Research Council report cited the FBI statistic that approximately one-third of primary suspects in rape cases are excluded by using DNA evidence.
The International Society for Forensic Genetics promotes scientific knowledge in the field of genetic markers analyzed for forensic purposes. Many Americans first became aware of the use and importance of DNA evidence
FIGURE 9.8 Visual representation of the size of a nanometer SOURCE: "The Incredible Tininess of Nano," in Nanotechnology: Shaping the World Atom By Atom, National Science and Technology Council, Committee on Technology, The Interagency Working Group on Nanoscience, Engineering and Technology, 1999, http://www.wtec.org/loyola/nano/IWGN.Public.Brochure/ (accessed March 14, 2005)
during the sensational and widely publicized 1994 trial of O. J. Simpson for the alleged murder of Nicole Brown Simpson and Ron Goldman. Nicole Simpson's blood was found in O.J. Simpson's vehicle and house, but the defense discredited the DNA results by claiming that sloppy police investigation had caused the samples to be contaminated and, alternatively, that the blood was "planted" in an attempt to "frame" Simpson.
A nanometer—the width of ten hydrogen atoms laid side by side—is among the smallest units of measure. It is one-billionth of a meter, one-millionth the size of a pinhead, or one-thousandth the length of a typical bacterium. Figure 9.8 shows the incredibly tiny scale of nanometers. According to an NIH definition, nanotechnology
involves research and technology development at the atomic, molecular, or macromolecular levels in the dimension range of approximately 1–100 nanometers to provide fundamental understanding of phenomena and materials at the nanoscale and to create and use structures, devices, and systems that have novel properties and functions because of their small and/or intermediate size. The novel and differentiating properties and functions are developed at a critical length scale of matter typically under l00 nm. Nanotechnology research and development includes control at the nanoscale and integration of nanoscale structures into larger material components, systems, and architectures. Within these larger scale assemblies, the control and construction of their structures and components remains at the nanometer scale.
Nanotechnology is sometimes called molecular manufacturing because it draws from many disciplines (including physics, engineering, molecular biology, and chemistry) and considers the design and manufacture of extremely small electronic circuits and mechanical devices built at the molecular level of matter. Researcher K. Eric Drexler, a founder and current chairman of the Foresight Institute, a nonprofit educational organization established to help prepare for advanced technologies, coined the term "nanotechnology" in the 1980s to describe atomically precise molecular manufacturing systems and their products. Drexler considers it an emerging technology with the potential to fulfill many scientific, engineering, and medical objectives.
Researchers anticipate a myriad of practical applications of nanotechnology such as home food-growing machines that could produce virtually unlimited food supplies and chip-sized diagnostic devices that would revolutionize the detection and management of illness. Investigators envision computer-controlled molecular tools much smaller than a human cell and constructed with the accuracy and precision of drug molecules. Such tools would enable medicine to intervene in a sophisticated and controlled way at the cellular and molecular level—removing obstructions in the circulatory system, destroying cancer cells, or assuming the function of organelles such as the mitochondria. Other potential uses
of nanotechnology in medicine include the early detection and treatment of disease via exquisitely precise sensors for use in the laboratory, clinic, and in the human body, plus new formulations and delivery systems for pharmaceutical drugs. In "Nanocontainers Deliver Drugs Directly to Cells" (Scientific American, Special Edition, April 18, 2003), Sara Graham described how researchers at McGill University in Montreal have developed tiny drug delivery vehicles that are able to pass through the cell wall of a rat and even penetrate some cell parts such as the mitochondria and Golgi apparatus. Such highly refined and specific drug delivery systems may enable physicians to administer smaller doses of toxic medications more safely. In the not-too-distant future, "nanorobots" may act as programmable antibodies. As disease-causing bacteria and viruses mutate to elude medical treatments, the nanorobots could be reprogrammed to selectively seek out and destroy them, and others might be programmed to identify and eliminate cancer cells, leaving normal cells unharmed.
The technology may also be used to develop immediately compatible, rejection-resistant implants made of high-performance materials that respond as the body's needs change. Nanotechnology will lead to new biomedical therapies as well as prosthetic devices and medical implants. Some of these will help attract and assemble raw materials in bodily fluids to regenerate bone, skin, or other missing or damaged tissues. Nanotubes that act like tiny straws could conceivably circulate in a person's bloodstream and deliver medicines slowly over time or to highly specific locations in the body.
NEW DEVELOPMENTS IN NANOMEDICINE.
In an article in the Washington Post ("Nanomedicine's Promise Is Anything but Tiny," January 30, 2005), Rick Weiss described some recent applications of nanotechnology to medicine, including:
Quantum dot diagnostics—tiny bits of silicon just a few atoms in diameter—are being used to track the movement of substances in cells and to identify diseases in blood or other tissue.
Tiny amounts of amino acids adhering to nanofibers that help nerve cells to heal and grow are delivered, suspended in a liquid gel called a nanogel.
Photo-thermal nanoshells—gold-coated spheres just 130 nanometers in diameter absorb near infrared light can be inserted deep into the body to the site of a tumor and heated to 122 degrees Fahrenheit, frying the tumor but not the surrounding tissue.
Another diagnostic application of nanomedicine was detailed in "Nanoparticle-Based Detection in Cerebral Spinal Fluid of a Soluble Pathogenic Biomarker for Alzheimer's Disease" (Dimitra G. Georganopoulou, Lei Chang, Jwa-Min Nam, C. Shad Thaxton, Elliott J. Mufson, William L. Klein, and Chad A. Mirkin, Proceedings of the National Academy of Science, vol. 102, no. 7, February 4, 2005). The Northwestern University researchers reported how nanoscience enabled ultrasensitive detection of a biomarker for Alzheimer's disease, a neurodegenerative dementia that afflicts an estimated four million people in the United States. Until recently, Alzheimer's disease could only be conclusively diagnosed after death, when brain tissue could be examined for the plaques and neurofibrillary tangles that are the hallmarks of the disease.
Specific peptides—amyloid-derived diffusible ligands (ADDLs)—are believed to be the causative agent in memory loss associated with Alzheimer's disease. The Northwestern University researchers developed a biobarcode assay, which is 100,000 times to one million times more sensitive than other available tests in the detection of ADDLs in the brain linked to Alzheimer's disease. The investigators hope that detecting ADDLs and other protein markers at significantly lower concentrations than conventional tests will lead to earlier diagnosis and intervention as well as development of new therapies for Alzheimer's and other diseases.
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