Cancer and Oncogenes
|Cancer is a group of diseases characterized by
the uncontrolled growth of cells. The division of most normal cells is under very tight
control. The differences between normal and tumor cells are readily apparent in the
laboratory. Microscopic examination of cells reveals profound differences in morphology.
Many normal cells have a flattened,elongated shape and they stick tightly to the plastic
dishes in which they are generally grown. Tumor cells are generally much rounder and do
not adhere tightly to the substrate.
Differences in growth properties are also readily apparent. Most normal cells placed in culture in the laboratory grow until they form a la monolayer that completely covers the bottom surface of the culture dish.. Once this monolayer is formed cell division ceases. When tumor cells are placed in culture, they grow to much higher cell densities. Tumor cells grow in "piles" (or multilayers) and they continue to grow even when the surface of the culture dish is completely covered (as long a there are sufficient nutrients).
Tumor formation is initiated via the conversion of normal cellular genes, called protooncogenes, into oncogenes. This conversion is a result of mutation (a change in the DNA sequence). Only a small minority (somewhere around one hundred or so) of the tens of thousands of genes in a cell can be converted to oncogenes.
The biological function of protooncogenes is not to cause cancer. That is, these genes are not just "sitting there" waiting to cause cancer. Rather these genes encode proteins that are part of the signal transduction pathways which control normal cellular growth and differentiation. Converting a protooncogene to an oncogene results in "throwing a monkey wrench" into the cellular "machinery". The result is the altered growth properties that we characterize as oncogenic transformation.
|Copyright © 2000, 2007 F.R. Gorga||Last update: