Why is DNA important?

DNA is the chemical basis of life.

Life is a manifestation of DNA.

Living creatures have such complex structure and behavior, how can only one molecule possibly be responsible? It can't.

However, the essence of life is replication. Life is possible because living organisms are capable of reproducing to produce progeny similar to the parents. Some die, but the process of reproduction insures that the group, or species, usually survives. Without long term survival of species through many generations, evolution could not occur. Without evolution there would be no life.

DNA is the only molecule in an organism that can replicate.


DNA is only a minor component.

DNA may be only one percent of the total mass of a cell. Many other molecules, e.g. proteins, are specific to the organism, and are absolutely required for it to function. The chart at the left summarizes the composition of a typical bacterium. However, DNA, directly or indirectly, controls the synthesis of all the other molecules.

DNA is the molecular blueprint for the cell.

The basic cycle

DNA is found in the nucleus of cells (the N of DNA) associated with chromosomes. The genes, segments of DNA, are copied by enzymes to make RNA. RNA is then translated by a very large complex of enzymes into proteins. Some of these proteins are the very enzymes that make RNA and translate the RNA into proteins. Finally, some proteins are the enzymes that enable the DNA to replicate.

The first two arrows, from DNA to RNA, and RNA to protein, represent information flow. However, the last arrow, protein to DNA represents cause and effect, but not information flow. The information needed to replicate DNA is in the DNA itself. Whatever the information flow, the complete cycle is needed for life, so all components (including many not shown here) are important to the living organism.

What is making who?

Sparky the cat needed his DNA to build himself, with a little help from his mother of course. If all the DNA in this adult were to disappear in an instant, he could continue to drink milk and chase mice. Sparky might think he could do without DNA, but in a few days he would know better. There are several tissues, e.g. blood and the endothelial layer of the intestine, that are continually being replaced by replication of stem cells, and once DNA is gone, that can't happen. As these short lived cells die out, he would become sick and die, with symptoms similar to radiation sickness. This is not coincidental, since a major effect of ionizing radiation is destruction of DNA. Of course, without DNA he also can't have children, and thus can't contribute to the species. If too many cats loose their DNA the whole species dies out, and Sparky has died in a very fundamental, existential way.

The DNA needs the cat to protect it from a harsh environment, and to supply energy for it to replicate. The fact that Sparky is likely to mate with a female, thus forming cells containing a mixture of DNA from the two cats means the DNA will populate a varied group of children. This gives it a greater chance of being inside a cat with characteristics that will insure its survival.

Is DNA making the cat, or is the cat making DNA?