How do genes control the growth and division of cells?

Several different genes control the growth and division of cells through the cell cycle. This organized process ensures accurate DNA replication, proper distribution of chromosomes to daughter cells and repair of DNA errors. Checkpoints within the cell cycle monitor for abnormalities, pausing the process to facilitate repairs if necessary. Cells encountering irreparable DNA damage may undergo apoptosis. This eliminates dysfunctional or surplus cells, with the remnant recycled by macrophages. Regulatory genes or oncogenes encode proteins that stimulate cell growth and division. When activated, these proteins promote cell cycle progression and proliferation. Examples of regulatory genes which exhibit greatest expression in G1/S phase include E2F1, CHAF1A, and BARD1. Regulatory genes which exhibit greatest expression in the S phase include PRIM1, RFC2, and RRM2. Conversely, other genes known as tumor suppressor genes encode proteins that inhibit cell growth and division. These proteins function to halt the cell cycle, preventing uncontrolled proliferation. Examples of tumor suppressor genes include p53, INK4, and PTEN.