dna_technology

Biologists in Japan have developed the world's first light-emitting mammals. The researchers injected DNA from a light-emitting marine organism into mouse zygotes to create genetically altered mice that glow green under UV rays. The DNA of the green mice is **//recombinant DNA//**, DNA in which genes from two different sources are linked. This research is only one example of how molecular biologists are using **//genetic engineering//**, the direct manipulation of genes for practical purposes. Using biochemical and mechanical tools of DNA technology, scientists can make recombinant DNA in vitro. They can then introduce the DNA into cultured cells that replicate the DNA and may express its genes, yielding a desired product. DNA technology has launched a revolution in biotechnology. In broad terms, **//biotechnology//** is the manipulation of organisms or their components to perform practical tasks or provide useful products. DNA technology makes it possible to clone genes for basic research and commercial applications. All of the following techniques are completely genious, but some are also unethical.
 * __General__**

Naturally occurring DNA molecules are very long, and a single molecule usually carries many genes. A particular human gene, for example, might constitute only 1/100,000 of the chromosomal DNA molecule where it resides. DNA molecules are structurally and chemically closely related; the distinctions between a gene and the surrounding DNA are slight, consisting only of differences in nucleotide sequence. To work directly with specific genes, scientists need to develop methods for preparing well-defined, gene-sized pieces of DNA in multiple identical copies. In other words, they needed techniques for **//gene cloning//**.
 * __DNA Cloning__**



Gene cloning and genetic engineering were made possible by the discovery of enzymes that cut DNA molecules at a limited number of specific locations. These enzymes are called **//restriction enzymes//**. These enzymes protect the bacteria against intruding DNA from other organisms, such as viruses or other bacterial cells.They work by cutting up the foreign DNA. The below figures is a diagram of a DNA molecule containing a recognition sequence, or **//restriction site//**, for a particular restriction enzyme. The restriction enzyme cuts a DNA molecule in a reporducible way, or **//restriction fragments//**. The restriction fragments are double-stranded DNA fragments with at least one single-stranded end, called a **//sticky end//**. Complementary ends will stick to each other by hydrogen bonding. These DNA fusions can be made permanent by the enzyme **//DNA ligase//**, which seals the strands together.
 * __Restriction Enzymes Are Used to Make Recombinant DNA__**

The original plasmid is called a **//cloning vector//**, defined as a DNA molecule that can carry foreign DNA into a cell and replicate there. Bacteria are the most commonly used host cells for gene cloning because of the ease in which DNA can be isolated from and reintroduced into cells. Bacterial cultures also grow quickly, rapidly replicating any foreign genes they carry. The following diagram shows how we might clone a eaukaryotic gene in a bacterial plasmid. Extra Vocabulary
 * __Genes Can Be Cloned In Recombinant DNA Vectors__**
 * //**Nucleic acid hybridization**//: base pairing between the gene and a complementary sequence on another nucleic acid molecule.
 * //**Nucleic acid probe**//: complementary molecule, short single-stranded nucleic acid that can be either RNA or DNA.
 * //**Denaturation**//: the separation of a DNA's two strands.



//PCR//**, the //**polymerase chain reaction**//, is a technique by which any piece of DNA can be quickly amplified (copied many times) without using cells. The DNA is incubated in a test tube with a special kind of DNA polymerase, a supply of nucleotides, and short pieces of synthetic single-stranded DNA that sere as primers for DNA synthesis. With automation, PCR can make billions of copies of a targeted segment of DNA in a few hours, significantly faster than the days it takes to clone a piece of DNA by making a recombinant plasmid and letting it replicate within bacteria.
 * __PCR (Polymerase Chain Reaction) Clones DNA Entirely in Vitro__



The whole nucleotide sequence of a genome is the ultimate map. The most dedicated research project made possible by DNA technology is the **//Human Genome//** **//Project//**. This is an international effort to map an entire human genome, determining the complete nucleotide sequence of DNA of each human chromosome. One of the stages of this project is DNA sequencing. The nucleotide sequence of a fragment can be determined by a sequencing machine. This procedure involves DNA labeling, DNA synthesis involving special chain-terminating nucleotides and high resolution **//gel electrophoresis//** - which separates nucleic acids or proteins on the basis of size, electrical charge, and other physical properties. The new strand that is found by the DNA sequencing then can be read and matched up.
 * __DNA Sequencing__**



Gene manipulation combined with a deeper understanding of gene function in the body may some day enable medical scientists to correct genetic disorders in individuals. The procedure is as follows: a cloned gene (normal allele, absent from the patient's cells) is inserted into a retrovirus. The retrovirus is then allowed to infect the cells that have been removed from the patient and cultured. Viral DNA carrying the normal allele is inserted into chromosome. This is then injected into the patient. This procedure may, in the future, be able to replace the defective alleles in people with a functional, normal allele using recombinant DNA techniques.
 * __[|Human Gene Therapy]__**



Disease-causing alleles can be detected with high accuracy by testing for the presence of [|RFLP] (restriction fragment length polymorphism) markers that are very close to the gene in question. RFLPs are detected and analyzed by **//Southern blotting//**, which is a hybridization technique that enables researchers to determine the presence of certain nucleotide sequences in a sample of DNA, therefore distinguishing DNA from different alleles.
 * __Forensic Uses of RFLP__**



Creating an identical person with the exact same appearance, traits, and characteristics of a person already in existance, or previously existing; this would occur by using the genes of the original person. This of course is the most controversial technique of DNA technology because of the ethics involved in tampering with God's will of death and survival.
 * __[|Human Cloning]__**