Wetware: A Computer in Every Living Cell by Dennis Bray

Author:Dennis Bray [Bray, Dennis]
Language: eng
Format: epub, mobi, pdf
Published: 2010-03-03T05:05:00+00:00

Each case probably has to be considered on its own merits, and the reasons for a lack of detectable effect will be different for each. But Be Weiringa has perhaps the most accessible system for analysis. Pathways of energy metabolism are so well understood that it is possible to understand how they function in the absence of particular enzymes. His answer to the puzzle, in broad terms, is that knockout mice compensate for defects by rerouting metabolic pathways. Other enzyme activities in the defective animals change in level so that they shoulder transformations normally performed by creatine kinase. In other words, he thinks that the mouse brain contains a network of complementary enzymatic pathways. When brain creatine kinase is deleted, other systems adjust their activities to restore the metabolic-energy supply. It is, of course, exactly what you would expect from the neural-network view of cell reactions: functions are shared among multiple units (that is, enzymes) so that the effects of damage to any individual unit or connection are mitigated. Graceful degradation indeed!

But wait a minute ... isn't there something fishy here? If the enzyme creatine kinase can be removed without effect, why does the mouse bother to make it in the first place? Why does it make all the other genes that have been shown to be dispensable? Why doesn't the animal simply delete the redundant genes and save itself unnecessary expenditure of material and energy?

The answer is a biological one and comes from the realities of survival in the world. In every case that has been closely examined, gene knockouts do have some effects. They might be subtle and difficult to find under laboratory conditions, but the mutated mice are unquestionably defective. In the cruel killing fields of their natural environment, those mice would almost certainly die before their time. Wild animals live on the brink; they are assailed from all sides by predators and parasites; they face starvation and disease daily. Any inherent weakness, such as poor hearing or a less than optimal ability to remember places, will make them relatively vulnerable under stress losers in the game of life. Even if these mice did manage by good fortune to survive and produce a litter, their pups would inherit the deficiency. Sooner or later the lineage would disappear from the gene pool. The resilience revealed in knockout experiments would not protect the species.

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