The Amazing World of Human Cell
The Introduction to Human Cell
Every human being begins life as a single cell, a fertilized egg; by the time he reaches adulthood, his body consists of 100 trillion cells. The cell is the fundamental component of all living things. As cells deteriorate, people age. As cells malfunction, people get sick. If cells were better understood, people might live longer and stay healthier. And, thanks to a recent series of extraordinary breakthroughs, scientists are beginning to learn more about them.
Scientists discovered three centuries ago that living things contain cells, but only in the last three decades have they begun to piece together the puzzle of how cells operate. They know a few fundamental things: every single adult cell (except ova and sperm) contains the same set of genes as the original cell. Still, cells come in all shapes, sizes and functions: slim nerve cells, more than 3 feet long and about 1 forty-thousandth of an inch wide, transmit impulses between the limbs and the brain; red blood cells, sculpted like poker'chips and 3 ten-thousands of an inch in diameter, carry life-giving oxygen around the body. But 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.
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 and danger. Disciplined biological armies stand ready to grapple with invaders. A centralized genetic government maintains order.
Just like political institutions, cells occasionally go wrong. Recycling systems can break down, overloading the cells with their own toxic garbage; the result is the fatal Tay-Sachs disease, or some similarly horrendous genetic ailment. Confused by erroneous information, internal factories can add so many chemicals to an already abundant supply that they eventually flood the whole body; the resulting accumulations of cholesterol lead directly to cardiovascular disease. A breakdown in communications between the nuclei of cells and their outer borders can produce the unrestricted, growth that causes cancer.
Even if they operate smoothly, normal cells eventually succumb to old age — the process of biological decay that alters the cells and kills the organisms of which they form the basic units.