Music of Life

Music of Life

Without a doubt, we humans perceive the world differently than a tree does. But down deep, at the molecular heart of life, the trees and we are essentially identical. We both use nucleic acids for heredity; we both use proteins as enzymes to control the chemistry or our cells. Most significantly, we both use precisely the same code book for translating nucleic acid information into protein information, as do virtually all the other creatures on our planet.

The genetic code turns out to be not quite identical in all parts of all organisms on the Earth. At least a few cases are known where the transcription from DNA information into protein information in a mitochondrion employs a different code book from that used by the genes in the nucleus of the very same cell. This points to a long evolutionary separation of the genetic codes of mitochondria and nuclei, and is consistent with the idea that mitochondria were once fee-living organisms incorporated into the cell in a symbiotic relationship billions of years ago. The development and emerging sophistication of that symbiosis is, incidentally, one answer to the question of what evolution was doing between the origin of the cell and the proliferation of many celled organisms in the Cambrian explosion.

We humans perceive the world differently than a tree does. Photo by Elena

The usual explanation of this molecular unity is that we are, all of us – trees and people, angler fish and slime molds and paramecia – descended from a single and common instance of the origin of life in the early history of our planet. How did the critical molecules the arise?

The molecular building blocks must be put together in the correct sequence. Life is certainly more than the amino acids that make up its proteins and the nucleotides that make up its nucleic acids. But even in ordering these building blocks into long chain molecules, there has been substantial laboratory progress. Amino acids have been assembled under primitive Earth conditions into molecules resembling proteins. Some of them feebly control useful chemical reactions, as enzymes do. Nucleotides have been put together into strands of nucleic acid a few dozen units long. Under the right circumstances in the test tube, short nucleic acids can synthesize identical copies of themeselves.

No one has so far mixed together the gases and waters of the primitive Earth and at the end of the experiment had something crawl out of the test tube. The smallest living thing known, the viroids, are composed of less than 10,000 atoms. They cause several different diseases in cultivated plants and have probably most recently evolved from more complex organisms rather than from simpler ones.