The DNA passed on from one generation to the next is a copy (though not always perfect). The cell that carries the DNA is also a copy (also not always perfect). In order for a cell to give rise to daughter cells, both the DNA and the cell have to be copied (replicated – ‘replicate’ means ‘to make a copy’). The only difference between copying a cell and copying DNA is that the cell copies itself by growing (copying its own detailed structure gradually, which is an example of self-templating) and then dividing so that each daughter cell has a full complement of the complex cell machinery and its organelles, whereas copying DNA for the purpose of inheritance occurs only when the cell is dividing.
Moreover, the complexity of the structure in each case is comparable. See Noble (2011) Differential and Integral views of genetics, particularly page 9: “It is therefore easy to represent the three dimensional image structure of a cell as containing as much information as the genome.”
My germ line cells are therefore just as much ‘immortal’ as their DNA. Moreover, nearly all of my cells and DNA die with me. Those that do survive, which are the germ cells and DNA that help to form the next generation, do not do so separately. DNA never works without a cell. It is simply an incorrect playing with words to single the DNA out as uniquely immortal.
I was also playing with words when I wrote that “DNA alone is inert, dead.” But at least that has a point. DNA alone does nothing. Cells can continue to function for some time without DNA. Some cells do that naturally, e.g. red blood cells which live for about 100 days without DNA. Others, such as isolated nerve axons or any other enucleated cell type, can do so in physiological experiments.
The point I am making is that functionality lies with the cell. DNA is an inert set of templates that the cell uses to make proteins and RNAs. Genes are therefore causes in a passive sense. They do nothing until activated. A set of proteins then initiates the process of transcribing the relevant templates. Active causation lies with proteins, membranes and the active functional networks they form. See Noble (2008) Phil Trans Roy Soc A, 366, 3001-3015
Distinguishing between the various senses of ‘cause’ is an elementary principle of philosophy. See chapter 1 of The Music of Life.
|The MUSIC of Life: Biology Beyond the Genome ©Denis Noble|