Our discussion of cell division using the replication of DNA by Herbert Taylor form the experimental basis for studies of the Cell Cycle. During these first studies relating researchers found that tritiated thymidine was going first into the interphase cells not prophase as expected. The basic experiment was to pulse cells with ³H-thymidine and start making slides of root tip squashes and determine the time necessary to find radiolabled metaphase figures. These data are presented as the number of labelled cells in metaphase as a function of time.

These results are more ofter depicted as a percentage of time

Important in the process is the concept of checkpoints .

The next set of discoveries relates to the factors regulating the cell cycle. Protein factors cyclins interact with proteins called cyclin-dependent kinases (CDK) to regulate the cell divisions.

Extra site for understanding the cell cycle?