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.