As a junior in college I experienced love at first sight. (No, I didn’t meet my wife then; that encounter happened during my sophomore year. I fell in love with my wife—who is also a biochemist—because there was such good chemistry between the two of us. But I digress.)
During my junior year I became enthralled with cell membranes. Of all the remarkable biochemical systems that constitute life, I found life’s molecular boundaries to be the most fascinating. In graduate school, I decided to focus my studies on cell membrane systems. Each day, I delighted in the opportunity to spend virtually all of my waking hours doing experiments and thinking about the structure and function of biological membrane systems, ultimately becoming an expert in the biochemistry and biophysics of cell membranes.
Cell membranes consist of hundreds of different phospholipid species and proteins organized as a bilayer. About a decade before I entered graduate school, S. J. Singer and Garth Nicolson proposed the fluid mosaic model to describe the structure of cell membranes. This description views the bilayer as a two-dimensional fluid composed of a complex mixture of phospholipids. The bilayer serves as both a cellular barrier and a solvent for a variety of integral and peripheral membrane proteins.
According to the fluid mosaic model, membranes are little more than haphazard, disorganized systems with proteins and lipids freely diffusing laterally throughout the bilayer.
It is remarkable how science progresses. The latest advances indicate that the fluid mosaic model is an incomplete depiction. Biochemists now acknowledge that cell membranes consist of a careful arrangement of molecular pieces that result in exquisite organization at the molecular level. This organization is integral to many functions performed by cell membranes.
Recent work adds to the evidence for cell membranes as a highly organized systems consisting of numerous structurally and functionally discrete domains. These domains, in turn, appear to be organized into supradomains, reflecting a hierarchy of order and organization. The unique functional role of each domain is dictated by distinct lipid and protein compositions.
Biochemists have discovered a special type of domain in cell membranes called lipid rafts. These domains are solid-like regions of the membrane that “float” in more fluid regions, like a raft on the sea. Typically, lipid rafts are enriched in cholesterol and sphingomyelins. Presumably, interactions between the lipid head groups maintain the structural integrity of the lipid raft.
Again, this organization is integral to many functions performed by cell membranes. For example, specific types of proteins, usually those involved in signal transduction, are associated with lipid rafts. High levels of protein receptors are embedded in lipid rafts. These receptors bind molecules in the environment and, in turn, initiate biochemical pathways that elicit a response by the cell in response to changes in its surroundings.
These new insights captivate my interest today, as much as they did when I was in college and a burgeoning scientist. New discoveries like these excite me for another reason. As I argue in The Cell’s Design, ordering and organization of the cell membranes is just one of a long list of a characteristic features of biochemical systems that provide evidence for the work of a Creator. Common experience teaches that it takes thought and intentional effort to carefully organize a space for functional use. By analogy, the surprising internal organization of cell membranes bespeaks of intelligent design.
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