Module 5 Cell Division

Reflect on the Big Picture

Finding the Fountain of Youth?

In addition to ignoring clues or checkpoints that essentially control cellular growth, cancer cells also never stop dividing. Probably the best example of this comes from cancer cells removed from Henrietta Lacks in 1951. Those cells are still in existence today. They are alive in a variety of laboratories around the world, and were even included in the Discover 17 satellite and shot out into space. Though Henrietta died eight months after the cells were removed, she has in some way reached immortality.

Healthy cells have a built in countdown timer. At best, a cell can divide approximately 50 times. After that, the cell will cause its own death, or self-destruct. Many cosmetic companies and late night TV commercials would like us to believe that we can cheat this number. That we can instead, keep our cells healthy and dividing as usual for longer and longer periods. Is this a reasonable claim? Can regular cells cycle continually?

Earlier in the lesson, we learned about the S phase of the cell cycle. During this phase the DNA is duplicated for the next generation of cells. This is crucial, since it is our DNA that contains all of the instructions necessary for cellular function. The problem is that our DNA accumulates errors over time. Whether it be from the duplication process itself or from exposure to environmental mutagenic agents, with time, our somatic cell DNA get’s pretty beat up. These errors found in DNA can cause serious problems or diseases like cancer. That’s why every cell contains specific instructions to self destruct after about 50 divisions. It seems our cellular clock exists for a good reason.

Discuss

Now that you have gained further knowledge on the cell cycle and its regulations or limits on cell growth, do you believe that research should continue to be focussed on finding a fountain of youth? Is it time to accept our limits and focus on the quality of our lives now rather than focus on the potential length of our lives? Discuss your opinion with your classmates and your instructor.

Lesson Summary

During this lesson, you were to explore the following focusing questions:

• What are the phases of the cell cycle?
• Do all cells have the same ability to reproduce and does this change with age?

Healthy cells will move through Interphase and M phase of the cell cycle when conditions are correct. From growth and production in G1, to the synthesis of DNA in S phase and all the way through and including the preparation of G2, the cell is constantly checking it’s own performance and readiness for the next step in the cycle. Finally, during M phase and cytokinesis, the cell will physically divide or split itself in two to form two new young cells, each of which contains one copy of the parent cell’s genetic instructions.

Regular cells have a limit to how many times they can divide, and they respect their neighbors. Cancerous cells do not respect either of these criteria, and this can have terrible results. If the fountain of youth is to be found by gaining control of our cellular division, it will not be by following cancer’s example!