Tuesday, June 18, 2013

Obeying Your DNA

Many of man’s construction strategies originate from our knowledge of what takes place in the nucleus of living cells. The human DNA molecule, present in virtually every cell nucleus, is a genetic blueprint capable of replicating itself precisely over hundreds of generations. Animals and plants with short life spans have transferred their genetic information over countless thousands of generations.

DNA has the potential for affecting all activities of the organism but it does not actually build and assemble the proteins from which the body is constructed. In addition to providing structural support for the body, proteins function in everything organisms do. They speed up chemical reactions and manage storage, transport, communications, movement, and bodily defenses. This is far from a complete list. In two major leaps, however, we arrive at the building and assembling area where proteins accounting for more than 50% of the dry mass of most cells are assembled.

The first of the two major leaps is the synthesis of the RNA molecule under the direction of DNA. The double stranded DNA molecule is first pried apart. RNA nucleotides attach to one DNA strand which acts as a template for new RNA molecules. RNA is chemically similar to DNA. It usually consists of a single strand. It is a faithful replica of the important functions of DNA. This type of RNA is called mRNA, or messenger RNA. If DNA could give directions to RNA, it may say to the newly created mRNA molecule, “Now carry your protein-building instructions to the next building site: Travel out of the cell’s nucleus and find your way to the cytoplasm outside the nucleus. There, organelles called ribosomes will help assemble amino acids into the thousands of proteins needed by the body.”

The protein-building code carried by the RNA molecules occurs in the form of triplets of nucleotides (molecular assemblages). In biology the nucleotides in DNA are abbreviated A, G, C, or T. Just by chance, 64 occurrences of A, G, C, and T of any three letters could occur. GCA, for example, could occur as a nucleotide triplet followed by other triplets—all different, all the same, or repeated in any combination. But only a few dozen triplets, called codons, are needed to specify the 20 life-specific amino acids, because all proteins needed in the human body are composed of only 20 amino acids. Only a few dozen of these 20 different chemical triplets become “code” for specifying the 20 needed amino acids. All human protein is composed of combinations of these 20 amino acids.

When we speak of cracking the code of life during the 1960s, we look beyond the landmark discovery of Crick and Watson concerning the structure of DNA and its possible role in genetics in 1953. Incredible follow-up discoveries were yet to come. Determining the structure of the DNA molecule was an event of startling importance. Following this, scientists longed to discover the even more astounding physical mechanism of the cell’s ability to code for proteins. Given the knowledge that the human body contains 50,000 to 100,000 different proteins, the question of how those proteins were designated, manufactured, and assembled assumed more importance beyond mere satisfaction of scientific curiosity.

Marshall Nirenberg discovered the secret of the triplet code in 1961. Knowledge of the code for the syntheis of all the human body’s proteins from 20 amino acids was solved before the end of that decade. Hargobind Khorana and Robert W. Holley shared the Nobel prize with Nirenberg for physiology and medicine in 1968. A colorful Wikipedia entry on Khorana states, “With this, Khorana and his team had established that the mother of all codes, the biological language common to all organisms, is spelled out in three-letter words: each set of three nucleotides codes for a specific amino acid.”

We marvel at the limitless number of proteins necessary to assemble the human body. Sources quote numbers of different proteins in our bodies at far greater than 100,000. Each of millions of other species of earth life is constructed from a varied combination of proteins. Unlimited varieties of protein-forming amino acids are possible in unique linear chains. We are struck with wonder at the knowledge of the Creator who designed our planet and caused it to teem with life.