The correct sequence of events in the cell cycle progression is monitored by a complex molecular mechanism , wherein the anchor points serve as signal transduction pathways , both operated upon detection of disturbances in the assembly of cellular structures , and in the normal course of subsequent stages of interphase and mitosis. The system of these points in time starts and stops the key enzymes controlling the cell cycle , and any signals of structural disruption or damage following reactions converts blocking DNA synthesis or by inhibiting the initiation of cell division. This fact is the reason for the domination of experimental work on the mechanisms controlling cell cycle progression by biology associated with medicine. Signaling pathways , and their interconnection network carrying information form from the external environment into the cell inducing a response to physiological or biochemical level . The paper presents the latest hypotheses describing operating principles : ( 1 ) activation of the signal system mitosis mediated phosphatase Cdc25 and (2) a cell cycle checkpoint . They suggest that the initiation of mitosis is the process of showing the characteristics of a bistable system , while checkpoints function , probably through mechanisms of positive and double - negative feedback loops , and the system depending on the type of substrate- product .