CONTENTS The Fundamental Unit of Life

The Fundamental Unit of Life The cell is the fundamental unit of life. Your health depends on what happens within the many different types of cells that make up your body. The health of your cells depends, in turn, on the function of millions of critical molecules. Click image for larger size This drawing of an idealized animal cell is based on photographs taken with powerful electron microscopes. Within the cell's membrane are such organelles as the mitochondria (energy producers), the rough endoplasmic reticulum (a site of protein production), the Golgi apparatus (a protein sorter), and the largest organelle, the nucleus (which contains the hereditary material DNA). In addition to these organelles, cells also contain an elaborate network of protein filaments called the cytoskeleton (not shown here) that anchor the organelles, maintain the cell's shape, and direct intracellular traffic. Since the mid-1940's, biomedical researchers have made enormous progress in identifying and understanding these molecules and how they interact in many cellular processes. Much of this research was "basic"--aimed simply at learning how living systems work. The fundamental knowledge developed through this research can lead to new ways to diagnose, treat, cure, or prevent disease. A stunning example of how basic cell biology research is moving toward practical application is found in studies of the cycle of cell growth and division. In recent years, many details of the biochemical mechanisms involved in the normal cell cycle have been discovered. Scientists have found the cell cycle to be regulated by highly complex interactions between pairs of proteins that belong to two general families. Work is proceeding at top speed to determine all of the many molecular interactions and the order in which they occur during the cell cycle. This work is yielding an understanding of the normal processes of growth and development that will, in turn, aid researchers seeking to treat diseases in which these processes go awry. Other scientists are discovering direct connections between cell cycle regulation and cancer. This research is beginning to demonstrate the specific role of oncogenes, genes that are directly involved in the development of cancer, and tumor suppressor genes, which are involved in cancer when their normal inhibitory functions are disrupted. To help readers understand some of the exciting biomedical research being conducted today, Inside the Cell provides an overview of the basic facts of cell biology. The brochure also contains some history of key scientific discoveries. Many scientists agree that the history of modern cell biology began with a convergence of improved techniques in microscopy and biochemistry. In the 1950's, as scientists working in these fields began to collaborate, they started to develop our current picture of the cell as a complex and highly organized entity. They found that a typical cell is like a miniature body containing tiny "organs," called organelles. One organelle is the command center, others provide the cell with energy, while still others manufacture proteins and additional molecules that the cell needs to survive and to communicate with the world around it. The entire cell is enclosed in a fine "skin," its surface membrane. This membrane not only keeps the cell intact, it also provides channels that open and close to allow selected molecules into and out of the cell. Scientists are seeking to learn more about the ways cells respond to outside signals, which are often conveyed when molecules bind to special receptors in cell membranes. Because the shape of a molecule plays a large part in determining its function, scientists are also keenly interested in determining the shape of important molecules and the rules that cause a string of chemicals to fold into a specific molecular shape. To understand cellular function, most scientists study parts of specific biochemical pathways, such as the cell cycle, that involve individual molecules, cells, groups of cells, and whole organisms. The goal is, of course, to be able to put all the parts together to understand normal cellular activities and how they malfunction in disease.