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Chapter Summary

The functions of cell organelles like the nucleus and mitochondria are critical to the processes on which life depends. But that does not mean they are easy to study. From a general biology course you probably learned facts like a nucleus controls the growth and reproduction of a cell and ribosomes are the sites of protein synthesis (Figure 13-1). But for a moment, take a step back and ask a more basic question, "How do we know these things?" Just seeing the microscopic structures inside a cell is hard enough. How can we know the way they actually work? For medical genetics, the next question is then obvious. What are the medical effects of a genetic change in the structure or activity of a cell organelle? Can that knowledge lead to appropriate treatment?

Figure 13-1.

Electron microscopy opens cell ultrastructure to a world of detail that could not be imagined by early researchers. But seeing structure does not always explain function. (Reprinted with permission from Cheville, N., Ultrastructural Pathology, Iowa State University Press, Ames, IA. p 2, 1994.)

Asking how we learn things about a structure as tiny as a cell organelle leads us to an important insight about the way science, including medical science, progresses. The real champion is how human ingenuity can figure out a process, especially a small, elusive one hidden somewhere in the complexity of the body—or of a cell. Let's step back in history to remind ourselves of both the limitations and the scientific revolutions that have been spurred by experimentation at the level of a cell. Then we will look at one specific example of discovering the role of a cell organelle.

Imagine yourself in the early 16th century. If you were a physician, not a common profession at the time, you would work with a limited and even misleading view of how the body functions. The prevailing explanation of life is a mystical one. But changes are underway. The publication of De humani corporis fabrica in 1543 by Andreas Vesalius helped introduce to science an emphasis on personal observation rather than a dependence on accepted authority. It replaced the authoritative position held by the studies that Galen published about 1300 years earlier. William Harvey's De motu cordis (1628) traced the flow of blood to and from the heart and led to a mechanistic, rather than a mystical, explanation of nutrient and oxygen transport. The invention of optics for magnification, which began as a novel entertainment, opened biologists to the microscopic realm.

Robert Hooke described the cellular structure of bark in Micrographia (1665)–"… these pores, or cells, were not very deep, but consisted of a great many little Boxes, separated out of one continued long pore, by certain Diaphragms …." This was the first use of the word ...

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