Hello Veny,
Thanks for your question. Congratulations on picking out an area to focus your science fair project!
This is a weighty but very interesting question, so we'll break it down. What we're looking at here is a question of why cells divide in the first place and what factors regulate cell cycles and cell division. Now, I'm assuming that you're familiar with the cell cycle itself (interphase with G1/S/G2, mitosis, cytokinesis). If not, you can check out these links for a refresher:
http://www.cellsalive.com/cell_cycle.htm
http://highered.mcgraw-hill.com/sites/0 ... works.html
Why do cells divide in the first place?
A cell will continue to grow until their need for resources becomes overwhelming or they experience difficulty moving nutrients and waste across their plasma membrane (the rate of transport slows because of cell volume). DNA overload also occurs where as the cell increases in size, it suffers an overwhelming amount of information and can not handle the volume. Division allows for replication of DNA material and decreasing volume.
What Factors Regulate Normal Cell Division and Cycles?
Various cells in the body have different growth rates: skin cells divide hourly, liver annually and nerve cells never divide. There are a variety of factors that signal to cells when to grow and when to stop. There are internal and external regulators. Internal regulators allow the cell cycle to proceed only once internal conditions and processes are met. What may interest you are
external regulators. External regulators direct cells to speed up or slow down the cell cycle, or growth factors as they stimulate growth and division of cells. Contact with other cells is one, or
Contact Inhibition. For example, when you get a papercut, your cells working to repair the area will quickly multiply until they reach the edges of the cut and then they stop. Molecules on the surface of neighboring cells also have the capability of causing cells to slow down or stop cell cycles, preventing excessive growth.
Growth signals to the cells depend on signal molecules, receptors, 2nd messenger molecules, cyclin nuclear proteins (or just cyclins) which concern themselves with normal cell division. An interesting area where you may be interested in directing your research is Cyclins, which regulate the timing of cell cycles in eukaryotic cells:
http://en.wikipedia.org/wiki/Cyclin
A good set of resources to look at regarding the cell cycle and regulation include the following links:
http://www.biochemweb.org/cell_cycle.shtml
http://en.wikipedia.org/wiki/Cell_cycle
http://biology.kenyon.edu/courses/biol1 ... er_07.html
Gene Expression and Regulation
Now, these growth factors are products of genes (or rather their expression), and as you know contain instructions for controlling when cells grow, divide and die. Now, what we need to ask is what sort of cell division we're looking at: normal/healthy or abnormal/injury. The mechanisms and factors that affect both are not too different, but one (normal) is well regulated and controlled by the body while the other (abnormal) is when the body loses control of this process.
Normal cycles are regulated by Proto-oncogenes while abnormal ones are regulated by oncogenes, which can speed up cell division. Genes that slow down cell division or cause cells to die at the appropriate time are called tumor suppressor genes. Many scientists are currently working with areas such as cancer biology to understand DNA mutations (changes) that "turn on" oncogenes or "turn off" tumor suppressor genes. Cancer and other malfunctions of cell division are attributed to these DNA mutations where the cell may stop responding to external regulators or stop producing internal regulators. Aside from genetic factors, these genes can also be turned on and off by environmental factors (such as radiation, chemicals, viral infections, direct injury to the cells or organs via things like smoking and alcohol). Interesting, not all types of cells are suspectible to cancer (such as cardiac tissue/cells) which carries the thought that these factors do in fact vary with the type of cell one is working with.
A great talk on this is done by Eva Vertes of Princeton University:
http://www.ted.com/index.php/talks/eva_ ... icine.html
Another good resource for a more complete looking into cell division and abnormal cell function is this document:
http://www.docstoc.com/docs/14975429/St ... and-Cancer
There are many great opportunities for a science project in this exciting area! Good luck in creating your project and hope this information will get you off to a great start in researching factors affecting cell division and growth and cell types.
-Melissa H.
