What happens at the G1 checkpoint of the cell cycle?

At the G1 checkpoint of the cell cycle, the primary focus is on assessing cell growth and evaluating resource availability. This is a critical moment that determines whether the cell is ready to proceed to the DNA synthesis phase (S phase). The cell checks for several factors, including size, sufficient nutrients, and the presence of growth factors that are necessary for DNA replication and cell division. If conditions are not favorable, the cell may enter a resting state known as G0, where it will not continue to divide until conditions improve. This checkpoint is vital because it helps prevent the replication of damaged DNA, thereby maintaining genomic integrity and proper cellular function.