Antoine Boutros

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Antoine Boutros

DNA: the keeper of the secret of life

Antoine Boutros - In our present series on the DNA we have demonstrated how this unique substance is the factor that passes genetic instructions from one cell to another. We must now deal with another complicated issue: how information passes from ancestors to descendants.

As we know, the embryo goes through many stages of development starting as a fertilized egg. This egg obtains all the genetic instructions inherited from the mother’s ovule and the father’s sperm. During fertilization, the nucleus of the sperm fuses with the ovum thus creating a fertilized egg that carries two groups of genetic information sourced from both parents: the mother and the father.

As the rounds of division kick off, the lone cell carrying 64 chromosomes splits into two cells. The chromosomes divide as well so that every daughter cell recovers its original number of chromosomes. Each of these chromosomes contains a DNA that carries genetic instructions and proteins responsible of producing all new substances necessary for the development and multiplication of the body.

Throughout the nine months that follow egg fertilization cells multiply thanks to a clever maneuver named “mitosis”. By delivery time, the body will have produced 200000000000 cells each of which is responsible for a specific function imposed by the instructions transferred by the DNA.

Although the DNA structure and the meticulous message delivered to the new cells are two extraordinary agents, there could not have been any life on earth if it were not for this substance’s outstanding capability to duplicate itself in order to pass information. It is noteworthy that the DNA replication process is one of the most striking wonders of nature.

When the chromosome is divided inside the cell, the double helix breaks into two vertical strands as if a zipper’s slider has opened up. Upon division, the pairs of nucleic bases (A with T and C with G) are broken and each base separates from its adjacent counterpart leaving at each side one strand with one exposed base. This strand would later complete itself by attracting the complementary bases present inside the cell. Thus, the old (A) base pairs up with a new (T) base while (C) reunites with (G) forming a new double helix over again. In other terms, the DNA duplicates itself noting that the duplication is an ongoing process that accompanies every cellular division.

To fulfill the development of the living organism and conclude the mission of life, the DNA nucleus releases a set of instructions in the form of a “genetic code” to construct new substances inside the cell. Scientists noticed that a type of genes labeled as “jumping genes” keep moving here and there in response to stimuli such as the environment rather than the instructions of the DNA.

The exciting part is that the DNA does not leave its stronghold inside the nucleus to pass its instructions. Rather, it empowers the messenger RNA (a braided molecule transcribed from the DNA template) with this mission. Messenger RNA carries coding information to the site of protein synthesis: the ribosome. Furthermore, the DNA produces other units known as the transfer RNA which transfers the amino acids or the raw materials of life to a synthesis line where a specific protein undertakes the production of the substance ordered by the Messenger RNA. Researchers also perceived that the DNA can also impact the memory. For all its primitiveness, the flatworm has proved to possess an astonishing memory. If we adapt the worm to shrink when exposed to a beam of light and then cut it in halves, the head half will grow a new tail while the tail half will grow a new head. Every daughter flatworm will remember what the mother flatworm did and will thus shrink when subjected to light. However if we submerge the tail half in a solution containing an enzyme that destroys the DNA, it will forget all that it has learned. Apparently, the memory can be washed and emptied which implies that the DNA and the proteins are connected to the storage of information. The oddity, however, is that the enzyme fails to influence the head half in the same manner. Although the different amino acids are restricted to twenty, there are thousands of proteins that differ from each other thanks to the DNA which in turn holds hundreds or rather thousands of instructions. Otherwise, no individual would have differed from the other.

The cell has finally unveiled its mysteries, one after the other, ushering science into an endless realm of intricacies and complexities namely the code of the secret of life which will be discussed in our next issue.

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DNA = Heredity

Antoine Boutros - Wondering about the availability of evidence that the DNA is the hereditary factor that transfers genetic instructions from one cell to another, was the closing statement of last month’s article. There are many answers to this question, the most evident are the following two:

First there is ample proof that similar cells have the same quantity of DNA. For instance, cells of the lizard-like amphibian Salamander, contain 168x10-9 mgs of DNA each, while cells of the Jelly Fish contain 1,42x10-9 mgs. Humans however, fall between the two with 6x10-9 mgs of DNA for every cell. No other material in cells of same species maintains the same quantity except the DNA itself

Apparently, quantities of DNA in living organisms are tightly connected to the complexity of these organisms. The DNA strand in viral chromosomes doesn’t exceed 1/2000 inch in length and has around 170 base pairs while bacterial DNA is 1/400 inch tall with 7 million base pairs. However, DNA in human cells (microscopic cells) may stretch to 3 feet (91,5 cm) and contain around 6000 million base pairs which makes it the tallest genetic recipe ever known. It is noteworthy that minor mistakes in base-pairing might lead to disastrous results inside the cell which might in turn bring about the birth of a freak or an abnormal offspring.

The second evidence is known as the “Transforming Principle” which was discovered by Avery who established that the DNA is the hereditary material. This experiment demonstrated that the DNA of dead bacterial cells has an impact even when injected in living bacteria. Should the injected DNA manage to penetrate the living cell, it would be mixed up with the chromosomes inside which allows instruction cloning or transfer into the living bacteria.

To confirm the validity of this principle, we may consider the following experiment: if we ignite a matchstick and place it near a crawling worm, the worm would burn once it reaches the flame. However, if this worm was eaten by a bigger one, and that bigger one was again exposed to the flame, it would change direction to avoid burning, which reveals that it has acquired a previous experience with fire thanks to the DNA transferred to its body.

Chemically speaking, the DNA is composed of three simple elements: sugar, phosphate and nitrogenous compounds called bases. The base is a substance that reacts with the acid to form salts and the four bases of the DNA are: A. T. G. C. On the face of it, nothing seems extraordinary about DNA, but in fact, its importance lies in its structure and its ability to duplicate itself and transfer hereditary instructions eternally, which makes it an infinite bank of information.

Upon examination of the double helix, we notice that the sugar and phosphate make up the sides of the two twisted strands while the nitrogenous bases point inward to form the steps of the staircase-like structure. Each base pair is formed from two complementary nucleotides that pair up with each other A with T and G with C. On the other hand, there is no specific pattern for the sequence or order of these pairs and any two bound pairs may be repeated for one, ten or hundred times. The different sequence in the nucleotide structure composed of base, sugar and phosphate, is the code that allows horses to deliver horses instead of elephants or roosters. It is also responsible for determining eye color, skin type, finger shape and so many other features. In other words, the length and structure of the sequence is what distinguishes every DNA and gives it specific instructions that differ from other DNAs. Thus, every hereditary trait would have its unique code based on the sequence of the bases inside the double helix that is inside the chromosome’s DNA. Even the process of life cannot go on unless the massive troops of proteins receive specific instructions from the DNA. As a matter of fact, the millions of proteins distributed over a thousand living organisms within it share one common property: they receive instructions from the DNA.

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