“The blueprints for the construction of one human being requires only a meter of DNA and one tiny cell. … even Mozart started out this way.” — L.L. Larison Cudmore
As creatures used to regarding ourselves as exceptional, humans must surely be humbled to realize that the instructions, for making one of our own, reside in a molecule so simple that scientists, for a very long time, did not believe could possibly contain enough information to build even a simple cell. But a large body of evidence, built up over the past century, supports Larison Cudmore’s assertion that the information for making you and me (and all the other kinds of living things in the world) is encoded in DNA. Tying in with Mendel’s observations about how characteristics are passed on from one generation to the next, the discovery that there was a molecule that carried this information, altered for ever how people thought about heredity.
The elucidation of the structure of DNA provided greater insights into how traits might be encoded in a molecule, and the ways in which the information is used by cells. As we learn more about this topic, scientists have remarked on how the information in our DNA resembles the programs that drive computers. While this analogy is a simplification, there is definitely a sense in which, as Richard Dawkins put it, “the machine code of the genes is uncannily computer-like”, with information in our DNA directly determining the properties of the proteins that run our cells. We know, as Ada Yonath described it, that, “DNA is a code of four letters; proteins are made up of amino acids which come in 20 forms. So the ribosome is a very clever machine that reads one language and operates in another. “
If this sounds strange, it is even more intriguing to realize DNA is copied and passed on from cell to cell, from one generation to the next. There is an unbroken line of inheritance from the first cell to every organism alive today. In the words of Lewis Thomas, “All of today’s DNA, strung through all the cells of the earth, is simply an extension and elaboration of [the] first molecule.”
The nature of this information, how it is copied and passed on, how it is read and interpreted, and how it gives rise to the cellular activities that we can observe, is the subject of this chapter. Another kind of information is also considered, towards the end of the chapter- the molecular information that cells receive from, and send to, each other. Overlaid on the instructions in the genes, this information provides cells with ongoing clues about both their own inner state and the environment around them. The interplay of these two kinds of information is responsible for the form and behavior of all living organisms.
Thumbnail: DNA double helix. Image used with permission (public domain; NIH - Genome Research Institute).