The genetic code, which carries the instructions on what a human (or any other living creature) will be like, from color of eyes to tendencies toward disease, is located in specific molecules called nucleotides inside the nucleus (center) of body cells. The genetic material, which is made up of acids in combination with sugar and phosphate molecules is called DNA (deoxyribonucleic acid).
In addition, RNA (ribonucleic acid), a simpler molecule, works closely with DNA by carrying its instructions to the parts of the cell where proteins are made. DNA is structured as a double helix, with two twisted strands parallel to each other with rungs like a ladder between the strands. Each strand consists of four chemical bases—guanine (G), adenine (A), thymine (T) and cytosine (C), while the "rungs" of the ladder are made up of sugar and phosphate.
These bases are repeated in particular arrays of sequences throughout the DNA molecule. The patterns they create provide the instructions on how cells will create proteins and what their tasks will be. DNA is packed into structures called chromosomes within the cell.
The discovery of the location of our genetic code began with agriculture. In the 1860s an Austrian monk, Gregor Mendel (1822-1884), showed through his pea breeding experiments that certain characteristics were passed from one pea generation to the next. But he did not know where the pea's genetic instructions were. In 1909 Russian-American chemist Phoebus Theodore Levene discovered DNA and RNA under the microscope, but could not determine their structure.
By the early 1950s, thanks to British chemist Francis Crick (1916-) and American biologist James Watson (1928-) and their discovery of the structure of DNA, scientists knew that genes were made of this nucleic acid and that specific cell proteins were the products of specific genes. The exact link between DNA and proteins was less well understood, however. Since proteins are considered the language of life, researchers believed that the DNA molecule might be the code for this language. This is how the term "genetic code" originated.
By the 1960s researchers had figured out the relationship between DNA and the cell proteins it gives instructions to, and the long process of finding the codes for specific traits was begun. Once a specific gene can be isolated, its code can then be copied and used to create synthetic genes, which can then be used to change the genetic structures in the human body. In this way, diseases that are caused by defective genes can be cured. Aside from these genetic engineering applications, Watson and his research lab at Cold Spring Harbor are currently working on mapping the entire genetic code (millions of different sequences) for the human body.
We still have a very long way to go in understanding the specific genetic codes for the millions of different traits that make up the human body, but the possibilities for the medical community alone are almost endless.
[See also Genetic engineering ]