Реферат: Dna Essay Research Paper What is DNA
Dna Essay, Research Paper
What is DNA?
Nucleic acid is a complex molecule found in all cells. There are two types of nucleic acids, deoxyribononucleic acid (DNA) and ribonucleic acid (RNA). DNA is found mainly in the nucleus of cells. RNA may be found throughout the cell. Even bacterial cells which do not have a nucleus, contain both DNA and RNA. Viruses, however, have only RNA or only DNA.
DNA plays a vital role in heredity and cell development. It is the substance in genes, the hereditary material that determines an organisms characteristics. Genes are located in chromosomes, the threadlike structures in the nucleus. When a cell divides, its chromosomes and genes are duplicated exactly and passed on to the two resulting daughter cells. The DNA in the genes of the daughter cells furnishes these cells with a complete set of instructions for their development.
DNA contains phosphate, a sugar called deoxyribose, and compounds called bases. These three components are arranged in chemically bonded units called nucleotides. In turn, the nucleotides are bonded to each other to form long chains called polynucleotides. There are four different bases in the nucleotide units of DNA – adenine, guanine, thymine and cytosine. The exact amount of each of these bases and the precise order in which they are arranged are unique for the genes of each species of living thing.
The chemical structure of DNA was first discovered in 1953 by biologists James D. Watson of the United States and Francis C. Crick of Great Britain. They proposed that the DNA molecule consists of two chains of polynucleotides arranged in a double helix (spiral). The two chains are held together by weak chemical bonds between specific pairs of bases. For example, adenine on one polynucleictide chain always bonds with thymine on the other chain. Simalarly, guanine on one chain always bonds with cytosine on the other chain. The DNA molecule looks like a twisted rope ladder. The polynucleotide chains of phosphates and sugars form the sides of the ladder. The matching bases, called base pairs, are the rungs that hold the chains together.
Before cell division, the cell duplicates its DNA. The two strands of polynucleotides separate lengthwise splitting between the base pairs. The separated strands serve as templates (molds) for the formation of new DNA molecules. The nucleus of the cell contains additional nucleotides. Each of the bases of these nucleotides bonds with its matching base on one of the templates. This matching process is repeated thousands of times to form a new DNA ladder that is identical to the original.
A national network of the DNA re-cords of convicted criminals will allow lo-cal law enforcement officials to make in-stant checks of genetic fingerprints, as they do already with traditional finger-printing.
DNA is left at crime scenes primarily in the form of blood, hair or semen. A DNA database can match samples taken from convicted felons and with DNA collected at the scene of a crime. The technique, when performed properly, is far more accurate than fingerprinting.
Until now, most states maintained their own DNA records without an easy way of sharing the information with their law enforcement counterparts. Unfortunately, criminals don’t always confine their violent behavior to a single state.
In a curious oversight, federal felons will not be part of the computer system; Congress must pass legislation allowing the collection of DNA from them first. A bipartisan bill authorizing such DNA collection ought to be passed, and quickly.
It comes as no surprise that the National Association of Criminal Defense Lawyers opposes such DNA databases. The defense lawyers say the information is an invasion of privacy.
Ridiculous. Convicted felons are not entitled to the same civil rights as law-abiding citizens. The moment they are found guilty of a felony they forfeit the right to keep their fingerprints or DNA records private.
Othergroups fear this is Washington’s first step toward a DNA database of all citizens. Collecting DNA from law-abiding people would indeed constitute an outrageous invasion of privacy. This FBI network will merely allow law enforcement officials to use another high-tech tool to help identify and catch criminals.