The Processes of Life: An Introduction to Molecular Biology by Lawrence E. Hunter

The Processes of Life: An Introduction to Molecular Biology by Lawrence E. Hunter

Author:Lawrence E. Hunter [Lawrence E. Hunter]
Language: eng
Format: epub
Published: 2011-05-26T09:09:00+00:00


7.4 Multicellular Life and Humanity

Most of the material covered up to this point is universal, or nearly so, among eukaryotes or metazoans. The molecular bases of development, gene regulation, protein production, DNA replication, and so on are the same in people as they are in mice, worms, and flies. It is these molecular homologies, in both structure and function, that have made it possible to understand so much about the biology that so many creatures share.

The preceding discussion of growth focused on the general problem of becoming big, but the particular mechanism responsible for human embryonic growth appeared only in the last sentence, and without much detail. Uterine support of embryonic growth occurs only in a few thousand species, far less than 1% of the million or so known species of animals. Other growth mecha nisms are more widespread, and more ancient. Since our heritage includes those mechanisms, it is likely that they remain within us, adapted perhaps to different or more restricted functions.

Nevertheless, biological understanding of the particular adaptations of our own species matters a great deal to us. More recently evolved functions, such as uterine development, and especially unique human capacities, such as language, are of particular interest. These recently evolved capacities are generated by quite small differences in DNA. Many protein coding sequences are quite highly conserved among all vertebrates, and variation within the mammals (including humans, mice, rats, dogs, cats, monkeys, and so on) is even smaller. Most of the genetic differences among mammals are in transcription factor binding and other regulatory sites (e.g., changing development), not so much in the proteins themselves.

These relatively small molecular differences, and the relatively smaller numbers of other species available for comparative studies make scientific progress more difficult. The molecular differences may be small, but the consequences for human health and well-being can be large. Consider the case of muscular dystrophy, a devastating genetic disease. The gene that is mutated in the disease, called dystrophin, was one of the first identified with the techniques of contemporary molecular biology. Yet progress on treating the disease remains poor, since that protein apparently plays a different role in humans than it does even in most other mammals. Creating a similarly mutated version of the mouse homolog of that gene has very little effect on the mouse, making it hard to study the disease mechanism in the laboratory. Dogs are affected in much the same way people are, but their slow development (compared to mice) and other differences makes it harder to use them to develop therapies.

Beginning in the next chapter, the focus will turn to the issues that are of importance to human beings, highlighting homologies whenever possible. Our anatomy and physiology shares much with other organisms, particularly other mammals, but there are also clearly aspects of our biology that are unique. Similarly, the diseases that plague human beings sometimes, but not always, affect other organisms as well. Fortunately for our knowledge of human biology, most of the features that shape us are



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