Presented scientific silhouettes awarded the 2001 Nobel Prize in physiology and medicine ? Leland Hartwell , Paul Nurse'a and Timothy Hunt , the pioneers of molecular mechanisms regulating the cell cycle . Their research mainly due to the detection of protein serine- threonine kinases called cyklinozależnymi , due to the regulation of their activity by specific protein ? cyclins . These kinases subsequently proved to be essential for normal cell cycle progression . Classic has become the concepts introduced by Hartwell START cycle checkpoints . They point to the importance of the regulation of cell proliferation need to integrate intra-and extracellular signals and precise monitoring of cells ready to move them into the next phase of the cycle after successful completion of the preceding phase . The article discusses the basic protein and is not regulated by processes in the cycle checkpoints activated by DNA damage (control points in phases G1 / S , S and G2) , or defects or irregularities in the formation of the mitotic spindle ( checkpoints in mitosis ) .