Lecture 13 - Immortalization and Tumorigenesis Flashcards
Define the term: “proliferative capacity”
Define the term: “Hayflick limit”
The measure of how many times a cell can divide before it either goes into senescence (usually) or dies off.
This limit, or plateau-ing on a graph, is known as the Hayflick limit and represent the maximum number of possible cell divisions. Usually this is ~50 divisions.
What are senescent cells?
Senescent cells are viable, but UNABLE to proliferate. As you age, more and more cells become senescent, and healing becomes harder and more time consuming.
What is so cool about embryonic stem cells? Is this ability shared by any other cell types?
Embryonic stem cells have unlimited replicative potential. Many cancer cells also have this unlimited replicative ability. Ex: HeLa cells.
Her name: Henrietta Lacks
Why can it take many years to develop a tumor? Approximately how many generations does it take?
It takes so long to develop a tumor because many mutated or cancerous cells die off early on due to apoptosis. It takes a long time to accumulate enough mutations (gradual process) in order to get the proliferative potential you need to get a tumor.
It takes ~30 generations to form a tumor.
What is the relationship between stressors and proliferation?
What can also cause cells to enter senescence?
Stressors can impose limitations on proliferation. Under stressful conditions, normal cells show an increased induction of tumor suppressor genes.
The overexpression of CDKIs can also cause cells to enter senescence (Go).
What allows cells to avoid senescence? What do you need to eliminate?
What is the consequence of bypassing senescence?
If you eliminate p53 and pRb, you callow cells to avoid senescence. This can be done with large T oncoproteins of SV40 virus.
Bypassing senescence will shorten your telomeres.
What happens when telomere ends shorten too far?
If telomere ends shorten too far, the chromatid ends become unprotected.
Following mitosis, the chromosome will attempt to protect itself by fusing together the two exposed sister chromatid ends.
Following mitosis again, the now fused chromatids will tear apart, leaving one longer with a section of the other.
A new point in fusion will form between longer chromatid and another chromatid, leaving two point of error.
Finally, the new fused chromatids will break apart once again leaving three points of error.
