Cells and Molecules - Brutes or Angels: Human Possibility in the Age of Biotechnology - page 29

notes
1. A scientific theory is the closest thing to “truth” that science offers. sci-
ence is non-dogmatic and self-correcting, so it never claims to own the absolute
truth. hypotheses about the physical world are tested with experiments designed
to invalidate the hypotheses if the hypotheses are wrong. After many experimen-
tal tests by many persons using many different approaches, a hypothesis may be
elevated to the level of theory. scientists feel quite confident about the ability of
theories to explain reality, but they are always open to new data that require dis-
carding a theory, revising it, or replacing it with a new theory. Albert einstein's
theory of general relativity replaced the classical newtonian theory of physics,
and Copernicus's heliocentric (sun-centered) theory replaced Aristotle's and
Ptolemy's geocentric (earth-centered) theory of the universe. The germ theory
of disease posits that bacteria and viruses cause infectious diseases, and the theory
of biological evolution posits that different life forms on earth have a common
ancestry.
2. Unaided human eyes see objects as small as 0.1 millimeters (0.0036 inches)
i in d ia meter.
3. Tem discerns smaller objects than light microscopy because the electron
beams used in Tem have a shorter wavelength than the visible light used in light
microscopes. The shorter the wavelength, the finer is the detail that can be seen.
4. lipids comprise a broad group of naturally occurring water-insoluble
molecules including fats (triglycerides), waxes, and sterols like cholesterol. Their
functions in cells include energy storage and membrane formation. The major
class of membrane lipids is phospholipids. one end of a phospholipid is water-
insoluble and the other end is water-soluble. in an aqueous environment, phospho-
lipids naturally form lipid bilayers, with their water-soluble ends facing outward.
5. research with mice shows that experimentally induced mutations in mito-
chondrial DnA cause diverse symptoms of premature aging, including graying
hair, hearing loss, and osteoporosis. But these results do not necessarily mean that
damage to mitochondrial DnA causes the normal aging process. for further in-
formation on this and other pathologies associated with dysfunctional mitochon-
dria see Karp 2010.