Home Random Thoughts Short pieces Long pieces Talk to Me

Long pieces

CREATION OF LIFE AND BIOLOGICAL EVOLUTION ( Page 2)
To understand life is to understand a cell. Easier said than done. Whether from a tissue in the human body, whether from a fruit fly or an ant, a cell is a cell and is not very different from the unicellular organisms like the amoeba or bacteria. To say that a cell is very complex shall be the understatement of the century. A detailed diagram of a cell from a biology textbook may resemble the map of a city. A cell resembles a city in the way things are organized, specialized, transported, utilized, consumed, waste products removed, security checks installed and so on and so forth.
Of all the myriad parts in a cell, the one part that carries in it the secret of life is the DNA (Dioxy ribonucleic acid). This is the part of the cell that holds the key to cell division or the art of self-replicating, the art of reproduction and survival, the art of life. The DNA also contains the genes that carry the hereditary traits from parents to offspring. The human genome contains about 30 000 genes while the simplest single celled organism contains around 500 genes. The double helix structure of the DNA is basically made of various combinations of the four bases, now simply called A, T, C, G (adenine, thymine, cytosine, guanine), making the rungs of the ladder while the guardrails are made of a nucleotide pair of sugar and phosphate. If each of these chemical units is taken for a letter of the alphabet, the DNA for the human being, the human genome, is a book containing three billion letters. It seems more apt to call it an encyclopaedia of 1000 volumes each of 1000 pages, each page containing 3000 letters. This “book of life” is the instruction manual for assembling the human body. One spelling mistake, one printing error, among these 3 billion letters can cause untold miseries; chronic illnesses, deformities, Parkinson’s disease and what have you. Even the cell of a simple organism like a fruit fly has a similarly complex DNA in which almost 50% of the genes are the same as in the human one. Most of the cells in our body contain all this DNA material in 46 chromosomes. The exceptions are the reproductive cells containing 23 chromosomes in each the male sperm and the female ovum. The red blood cells also do not possess the entire DNA as in other cells.
To say that our DNA is the instruction manual for assembling the human body may at first seem preposterous or at least a bad joke. Not if you understand the function of DNA in protein synthesis. Genes, units of heredity passed from parent to offspring, are pieces of DNA encoding the information for the synthesis of a specific protein. There is the danger of overlooking the significance of the phrase, “synthesis of protein”. Only recently did this significance dawn on me, even though I had known for a long time that protein synthesis is one of the functions of the DNA. Let us see how the DNA punch card or instruction manual is employed in assembling this human body.
When the sperm fertilizes the egg, life begins in the form of a single-celled zygote, which has a full complement of the entire DNA, half from the mother, half from the father. The DNA then gets busy directing the rest of the cell in the production of essential proteins, first for growth and then for cell division. During the cell division the DNA replicates itself into two full sets and then two cells are formed but do not separate. This process continues, two becoming four, eight, sixteen and so on. As the size of the embryo increases the number and variety of proteins needed for further growth also increases. The DNA continues to give clear instructions resulting in the synthesis of proteins needed for the tissues of muscle, bone, blood, brain and nerve cells as well as for various organs. The miracle of the growth of a zygote into an embryo, into a foetus, into an infant, into a child, into an adult, is made possible by the ability of the DNA to direct the rest of the cell to manufacture the right kinds of proteins at the right time and place. One has to be really naïve to think or believe that by the chance combination of some molecules non-living matter got the miraculous faculty called life, the extraordinary power to replicate itself.
Most of the cells as we know today contain, RNA molecules along with DNA. RNA, though not as complex as DNA, also shares the self-replicating capacity of the DNA and has important role to play in protein synthesis. One of these two is essential for life. Both are found in most cells of the higher animals and plants as well as in the single celled organisms, with the general exception of viruses which have only the DNA or the RNA, not both.