The Cell Division Cycle and the Biology of Cancer

As part of the cell division cycle, DNA is duplicated and then one copy is distributed to each new cell. The cell division cycle is divided into phases. G1, S, and G2 occur in interphase prior to chromosome separation in mitosis (M). S phase is the DNA duplication phase. The initiation of DNA replication, replication forks, and Okazaki fragments is discussed. Progression through the cell cycle is dependent on cyclin-dependent kinases (CDKs) and cyclins. Cancer occurs when there is uncontrolled cell division. The “Guardian of the Genome” the p53 protein tumor suppressor is a critical regulator, and its mutation occurs in more than 50% of cancers. The mutation or epigenetic change of oncogenes can also lead to cancer. Stem cells are good targets for cancer, but mature cells can dedifferentiate and also be a source of cancer cells. The cancer stem cell idea is discussed, particularly in the case of cancer recurring after remission. Drugs developed for chemotherapy increasingly strive for selectivity to inhibit key proteins involved in signaling the promotion of cell division and cell cycle regulation.