Schematic illustration of a typical cell. The nucleus contains the cell’s genetic “blueprint.” The remainder of the cell is filled with cytosol, a clear, water-soluble fluid. Specialized structures within the cytosol perform many of the cell’s functions. For example, mitochondria contain enzymes that generate most of the cell’s energy. A given cell may contain up to several thousand mitochondria. Each mitochondrion is surrounded by a two-layered membrane. The outer membrane controls the flow of substances into and out of the mitochondrion. The inner membrane is convoluted, providing extensive surface area for the attachment of enzymes. Enzymes