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By Root 962 0

true brain of the cell. Let’s put the membrane to the same “brain” test to which we put the nucleus. When you destroy its membrane, the cell dies just as you would if your brain were removed. Even if you leave the membrane intact, destroying only its receptor proteins, which can easily be done with digestive enzymes in the lab, the cell becomes “brain-dead.” It is comatose because it no longer receives the environmental signals necessary for the operation of the cell. The cell also becomes comatose when the membrane’s receptor proteins are left intact and its effector proteins are immobilized.

To exhibit “intelligent” behavior, cells need a functioning membrane with both receptor (awareness) and effector (action) proteins. These protein complexes are the fundamental units of cellular intelligence. Technically they may be referred to as units of “perception.” The definition of perception is “awareness of the elements of environment through physical sensation.” The first part of the definition describes the function of receptor IMPs. The second part of the definition, the creation of a “physical sensation,” sums up the role of the effector proteins.

By examining these basic units of perception, we have engaged in an ultimate reductionist exercise, taking the cell down to its fundamental nuts and bolts. In this regard it is important to note that at any given time there are up to hundreds of thousands of such switches in a cell membrane. Consequently, the behavior of a cell cannot be determined by examining any individual switch. The behavior of a cell can only be understood by considering the activities of all the switches at any given time. That is a holistic—not reductionist—approach, which I’ll elaborate on in the next chapter.

At the cellular level, the story of evolution is largely the story of maximizing the number of basic units of “intelligence,” the membrane’s receptor/effector proteins. Cells became smarter by utilizing their outer membrane surface more efficiently and by expanding the surface area of their membranes so that more IMPs could be packed in. In primitive prokaryote organisms, the IMPs carry out all of its fundamental physiologic functions including digestion, respiration, and excretion. Later in evolution, portions of the membrane that carry out these physiologic functions go inside, forming the membranous organelles that are characteristic of eukaryotic cytoplasm. That leaves more membrane surface area available to increase the number of perception IMPs. In addition, the eukaryote is thousands of times bigger than the prokaryote resulting in a tremendous increase in membrane surface area, i.e., a whole lot more room for IMPs. The end result is more awareness, which translates to greater survivability.

Through evolution, the cell membrane’s surface expanded, but there was a physical limit to that expansion. There was a point at which the thin cell membrane was not strong enough to contain a larger mass of cytoplasm. Think what happens when you fill a balloon with water. As long as the balloon is not overfilled, it is strong and can be passed around. However, if you exceed the balloon’s water capacity, the balloon ruptures easily, spilling its contents, just as a membrane with too much cytoplasm would inevitably rupture. When the cell membrane reached that critical size, the evolution of the individual cell reached its limit. That’s why for the first three billion years of evolution, single cells were the only organisms on this planet. That situation changed only when cells came up with another way to increase awareness. In order to get smarter, cells started banding together with other cells to form multicellular communities through which they could share their awareness, as I explained in Chapter 1.

To review, the functions required for a single cell to stay alive are the same functions required by a community of cells to stay alive. But cells started to specialize when they formed multicel-lular organisms. In multicellular communities, there is a division of labor. That division of labor is evident