Deoxyribonucleic acid
All living things carry a detailed set of instructions carrying the information necessary to develop and maintain physical life.
This living blueprint is present in the form of a double stranded chemical called DNA.
The Composition of physical Life
The human body is made up of about 10 trillion cells; most contain the entire human genome encoded as units of DNA. The red blood cells contain the entire human genome; everything you would need to build a human body. The information is encoded as units of DNA. The cell nucleolus contains DNA in 23 pairs of chromosomes. Each parent passes a set of these chromosomes to their offspring's. Between them the 46 chromosomes in the cell contains the DNA for about 100,000 genes, which serves as instructions in the human hereditary manual.
Each gene occupying a region of the chromosomes holds the recipe for creating particular molecules, usually proteins which are the work-horses of the cell.
The recipes consists of a characteristic sequence of the four chemical units of DNA known as Adenine, thymine, guanine and cytosine, or for short by their initials A. T. G. and C. These units can interlock with each other in only two combinations. A and T always couple together, and G and C always go together. The units connect with their partner on the opposing DNA strand. This means that the information on one strand exactly mirrors the second strand of the double helix.
Altogether the human genome contains about 3 billion units of DNA, packaged in the form of 23 chromosomes.
Two groups, the Celera Corporation of Rockville, Md., and an international consortium of academic centers supported largely by the National Institutes of Healtheven, differ on the size of the gene-coding part of the genome. Celera says it is 3.12 billion letters of DNA; the public consortium that it is 3.15 billion units, a letter difference of 30 million. Neither side can yet describe the genome's full size or determine the number of human genes.
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