APPENDIX
|
A PROTEIN PRIMER
Wonstration.
hat is a protein? Consider joining me in my kitchen for a little dem-
I pick out an egg from the carton and grab a bowl from the cupboard.
Chicken eggs are simple living structures composed of just a couple very large
cells, and the contents of these cells are easy to observe. Eggs are also potent
analogs for life and living bodies; they are full of substance and overflowing
with significance. The one in my hand is worth close examination.1 I crack
open the egg and in one half of the shell I catch the yolk, a massive, bright yel-
low single cell. The viscous whites of the egg drip over my fingers, until they
plop down into the bowl below. Rubbing my fingers together, I can feel the
slippery textures of the egg whites. What is this stuff made of?
When scientists divide this substance up into its molecular constitution,
like they do the rest of our foods, they find that it is mostly water. In addition
to the fats, trace minerals, vitamins, and sugars it contains, a mixture of pro-
teins accounts for about 10 percent of its weight. One particular protein, oval-
bumin, accounts for just over half of all the protein in the egg whites. If it had
been a fertilized egg, this is the protein that would have nourished a growing
chick.
When I look at the egg whites, however, all I see is a slippery, translucent
mass. Protein molecules are so small they lie beyond the limits of our percep-
tion. Even if I placed a sample on a microscope slide and applied the highest
power microscope lens, I still would not be able to see an individual protein
molecule.
Plate 1 in this book shows a crystallographic rendering, a three- dimensional,
atomic- resolution model of ovalbumin. What does it depict? What are those
two blobs that seem to be joined together? And those ribbon- like spirals that
thread through the molecule?
Previous Page Next Page