Experiments Dealing with Cell Cycle

Dr. Polymenis's Cell Lecture: Engine of the Cell Cycle Use of Oocytes in Cell Studies Experiments: Cell Division Conclusion

Experiments Regarding Cell Division

The following pictures are depictions of experiments dealing with the division of cells. Below them is an explanation of each.

Electrophoresis

The red line indicates cyclin

Lee Hartwell's Findings

Yeast bud in various cell cycle stages

Maturation Promotion Factor (MPF)

MPF

Lee Hartwell's Findings (continued)

Mutated yeast cells

Electrophoresis of Cyclin

The top picture shows a process called electrophoresis, which proves that cell division is dependent upon the presence of the protein cyclin. This is significant because it was the first time anyone discovered a macromoleule which outlined the process of cell division. The actual division points of the cell were correlated with the appearance and disappearance of the cyclin in intervals. The factor disappeared exactly when the cell began dividing, and reappered after division ended. The protein was named "cyclin", because its presence correlates with the cell cycle.

Budding Yeast Experiment

Lee Hartwell was a geneticist who succeeded in discovering Cell Division Cycle mutants (CDC's). In order to find the engine of cell division, he needed to find a specific type of mutation that was switchable or conditional. The most prevalent example of these mutants are temperature-dependent. Hartwell chose to work with budding yeast because, unlike most organisms, the cell cycle of budding yeast can be observed without killing the cells. The buds are visible on the surface as the cell cycle progresses. Hartwell attempted to mutate the yeast with organisms that are alive at 25 degrees Celsius, and dead at 37 degrees Celsius. In order to find the correct mutants, he placed them in a flask and observed the state they were in upon death. The ideal cells, or "good mutants", would go through the cell cycle, and become large and unbudded. All of the cells in this flask would thus have a uniform arrest. Hartwell kept the cells that died with uniform morphology to ensure that the same mutant was collected. These became known as CDC's. The most common of these is cdc28.

Maturation Promotion Factor

Dr. Masui looked at cyclin dependent kinase, which drives the cell cycle. This promotes protein phosphorylation, an event required for the cell to move from the G2 phase to mitosis. When this cyclin, or MPF, is injected into the oocytes, Masui discovered that they then divided at a rapid rate.