While each human cell performs its own specialized function, it also exerts influence on the cells around it. Cells communicate with one another via receptors, protein molecules on the cell surface. A cell releases chemical messages, which fit into the surface receptors of cells nearby, much as a key fits into a lock.
A cell may instruct other cells in its neighborhood to divide, for example, by releasing a growth-promoting signal, or growth factor. The growth factor binds to receptors on adjacent cells, activating a message within each individual cell. This message travels to the nucleus, where a cellís genes are located. Cancer begins in the genes, segments of the long, coiled molecule known as deoxyribonucleic acid (DNA). Genes govern the bodyís development and specific characteristics by providing critical instructions that trigger the production of proteins within the body. In cancer, certain genes fail to perform their jobs correctly. This computer-generated model shows two strands of deoxyribonucleic acid (DNA) and its double-helical structure.