Cell Cycle

Every living organism relies on cell division to grow, to replace worn-out or damaged cells, and to produce offspring. But division cannot happen in isolation — a cell that is about to split into two must first copy its genetic material and build up enough of its own components so that each new cell it forms is complete and functional. Because of this, three things must happen together in a carefully coordinated manner: the cell grows, its DNA is duplicated, and finally the cell divides. If these were not tightly synchronised, the daughter cells could end up with damaged or incomplete genomes.

The cell cycle is the name given to this whole ordered sequence of events — the series of steps through which a cell duplicates its genome (its complete set of DNA), manufactures the other materials it needs, and eventually splits into two daughter cells.

A few important points about how these events are timed and controlled:

• Cell growth is continuous. The increase in cytoplasm goes on steadily throughout the cycle rather than at one fixed moment.
• DNA synthesis is not continuous. Unlike growth, the copying of DNA is confined to just one particular stage of the cell cycle, not spread across the whole cycle. …