Each Cell Like a Walled City
A RECENT issue of “Newsweek” magazine explored the microscopic domain of human cells. The writers marveled at the tremendous variety of functions accomplished in such a small space: “Each of those 100 trillion cells functions like a walled city. Power plants generate the cell’s energy. Factories produce proteins, vital units of chemical commerce. Complex transportation systems guide specific chemicals from point to point within the cell and beyond. Sentries at the barricades control the export and import markets, and monitor the outside world for signs of danger. Disciplined biological armies stand ready to grapple with invaders. A centralized genetic government maintains order.”
Another fascinating operation of this diminutive “government” is its “postal service” that sees to it that manufactured proteins reach their proper destinations within the cell. “We think there is a zip-code system in the cell as there is in the Postal Service,” says a Rockefeller University scientist. Proteins manufactured by cell ribosomes are thought to be “addressed” with a code of 20 to 50 amino acids. The scientist says that “the surface of the correct organelle [cell part] recognizes the address and lets the protein in, like agents who recognize a visa and let you across a border.”
The magazine repeatedly commented on how little science knows about how cells accomplish what they do. For example, it points out that “researchers remain baffled by the arcane chemical mechanism that enables particular genes in different cells to switch themselves on and off and perform differently in varying circumstances.” The article also quotes Nobel prize-winner Christian de Duve of Rockefeller University: “What we have today is a description of what happens in the cell, not an understanding of how it happens.”
Throughout the article appear expressions such as: “The human cell and its organelles or interior parts still guard many secrets.” “Nothing mystifies biologists so much as regulation. Pancreas and eye cells, for example, both contain a gene that can produce insulin, but pancreas cells make insulin and eye cells do not.” Speaking of the way some genes seem to be held in a chemical grip so that they do not function in cells where they are not needed, it asks: “Why is one gene gripped tightly and another not? Scientists have no answer yet.” The article concludes: “Each answer seems to pose a new, more complex question about the cell. . . . if anything is certain in the minute and mysterious world of cells, it is that the human cell will never surrender all of its secrets.”