The cell cycle refers to the orderly series of events that make new daughter cells by dividing the existing cells. The cell cycle is required to produce new cells during growth and development, to replace the old and damaged cells, and to repair the tissue by adding the new cells. If the existing cells do not enter the cell cycle, new cells would not be formed to be added to the tissues of the organisms.
However, the cell cycle is regulated at several checkpoints to ensure that a cell enters the process only when the new cells are required by the body and the process is stopped once the required number of new cells are formed. Any deviation from the regulation of the cell cycle may make the cells to enter the uncontrolled cell division. It may even lead to cancer where the cells divide without any control and produce malignant tumors.
Enzymes are a type of protein that speed up chemical reactions. They are known as "biological catalysts." For example, your stomach would not be able to break down food if it did not have special enzymes to speed up the rate of digestion.