Trupti Kawli is a student at the Department of Molecular Reproduction , Development and Genetics, Indian Institute of Science, Bangalore. She is currently working on the development biology of the cellular slime mold Dictyostelium discoideum.

The cell theory proposed in 1838 by Theodor Schleiden and Jacob Schwann had two main tenets. One, every living organism is composed of one or more basic building blocks, cells, and two, new cells can arise only by the division of pre-existing cells. Thus, more than a century and a half ago it was apparent to biologists that cell division is the only path to cellular immortality. The complex sequence of events that produces two more or less indistinguishable daughter cells from the parent is the cell division cycle or the cell cycle. The task of dividing a cell is not as easy as it appears. It involves four things: the cell must grow (G1), replicate its DNA (S), segregate its chromosomes into two identical sets (G2) and then divide, that is, undergo mitosis (M) (Figure 1). A cell is faced with a number of problems if it wishes to produce two genetically identical daughter cells. These can be broadly listed as follows. Firstly, there is the completion problem, meaning that the cell has to follow a strict sequence of events in a linear fashion and ensure that the completion of one event causes the next. This guarantees that all the necessary events would have occurred before a daughter cell is born. Secondly, there is the alternation problem: events have to alternate with each other in a cyclic fashion such that no phase of the cycle repeats itself without the intervening occurrence of other phases. Leland Hartwell, Paul Nurse and Timothy Hunt were awarded the Nobel Prize in Physiology or Medicine for 2001 for their discoveries of key regulators of the cell cycle.

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Address for Correspondence
Trupti Kawli
Department of Molecular Reproduction, Development & Genetics Indian Institute of Science Bangalore 560 012, India.