In relation with Big Idea 2, (biological systems
utilize free energy and molecular building blocks to grow, reproduce, and to
maintain dynamic homeostasis) on pages 187-188, Dr. Moalem discusses how cancer
is caused by uncontrolled reproduction of cancer cells.
First,
define what the Hayflick limit is. Then,
explain the process of unlimited reproduction of cancer cells using the terms telomeres, telomerase, genetic loss, and Hayflick
limit. In addition, research and
identify one type of cancer cell that is able to ignore cellular signals that
command damaged cells to die through apoptosis, programmed cell death. How does this specific cancer cell ignore the
suicide command to perform apoptosis?
-Ken Saito
(ksaito4@students.d125.org)
In response to your question, on page 187, Moalem describes a Hayflick limit as a check on cancer, by preventing a cancerous cell from reproducing uncontrollably,"essentially shutting down tumor growth before it really gets going". This is an example of a past biology term we learned called negative feedback, where your body realizes that there is a cancer cell in the body and that they can reproduce rapidly, so the Hayflick limit is a threshold for the number of times the cancerous cell can reproduce before it "runs out of steam".
ReplyDeleteIn the process of unregulated cancer cell growth, telomeres are a region at the end of a chromatid that have repetitive nucleotide sequence, and when these telomeres die, the cells die and lose their ability to reproduce. However, cancers use an enzyme called telomerase to lengthen these telomeres, so that the cancer cell can keep reproducing rapidly and more efficiently because it takes longer for the telomeres to die. Because this telomere buffer never runs out, there is a loss of genetic information in the body and the Hayflick limit, the potent check against cancer is tricked because the threshold uses telomeres, but the telomeres have been manipulated by the enzyme telomerase. However, research has found that the enzyme telomerase, in this case used to help reproduce cancer cells, could potentially also help the immune system cells fighting the cancer because it could lengthen the telomeres of the immune system cells as well. (http://www.popsci.com/science/article/2011-07/man-who-would-stop-time?page=4)
A specific cancer cell called melanoma avoid apoptosis by inhibiting gene expression of the gene encoding Apaf-1. (http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/Apoptosis.html#aids). There are also many other types of cancer cells that can ignore cellular signals to essentially kill itself, and therefore survive and reproduce much longer. For example, B-cell leukemias express high levels of Bcl-2, blocking apoptic signals it may receive.
Rudy Viswanathan (aviswan4@students.d125.org)