Plunging into the Nucleus of the Cell

Plunging into the Nucleus of the Cell

If we plunged through a pore into the nucleus of the cell, we would find something that resembles an explosion in a spaghetti factory – a disorderly multitude of coils and strands, which are the two kinds of nucleic acids: DNA. Which knows what to do, and RNA, which conveys the instructions issued by DNA to the rest of the cell. These are the best that four billions years of evolution could produce, containing the full complement of information on how to make a cell, a tree or a human work. The amount of information in human DNA, if written out in ordinary language, would occupy a hundred thick volumes. What is more, the DNA molecules know how to make, with only very exceptions, identical copies of themselves. The know extraordinary much.

DNA is a double helix, the two intertwined strands resembling a “spiral” staircase. It is the sequence or ordering of the nucleotides along either of the constituent strands that is the language of life. During reproduction, the helices separate, assisted by a special unwinding protein, each synthesizing an identical copy of the other from nucleotide building blocks floating about nearby in the viscous liquid of the cell nucleus. Once the unwinding is underway, a remarkable enzyme called DNA polymerase helps ensure that the copying works almost perfectly. If a mistake out and replace the wrong nucleotide by the right one. These enzymes are a molecular machine with awesome powers.

The enzymes are a molecular machine with awesome powers. Illustration: Elena

In addition to making accurate copies of itself – which is what heredity is about nuclear DNA directs the activities of the cell – which is what metabolism is about – by synthesizing another nucleic acid called messenger RNA, each of which passes to the extra-nuclear provinces and there controls the construction, at the right time, in the place, of one enzyme. When all is done, a single enzyme molecule has been produced, which then goes about ordering one particular aspect of the chemistry of the cell.

Human DNA is a ladder a billion nucleotides long. Most possible combinations of nucleotides are nonsense: they would cause the synthesis of proteins that perform no useful function. Only an extremely limited number of nucleic acid molecules are any good for lifeforms as complicated as we. Even so, the number of useful ways of putting nucleic acids together is stupefyingly large – probably far greater than the total number of electrons and protons in the universe. Accordingly, the number of possible individual human beings is vastly greater than the number that have ever lived: the untapped potential of the human species is immense.