Cancers result from alterations in the genes that control cell proliferation, differentiation or apoptosis. Collins K et al (1997). Cells have a predictable way of proliferating, guided by internal machinery that controls such. Also, there are mechanisms to make sure that the process is error free. If there is any erring cell, there are mechanisms that make sure that the cell line is destroyed so that such defective cell is not perpetuated in the body system. All these processes are directed towards making sure that cancer cells do not develop. However, if there is any deviation from these check mechanisms, cancer cells may end up being formed. Bernards R (2012)
The cell cycle is tightly controlled by a family of kinases. These kinases tightly control the transition between cell cycle stages by a sequence of well timed regulatory phosphorylation and dephosphorylation. The cell cycle is also controlled by checkpoint control. These checkpoints sense defects in events of DNA replication and chromosome segregation. This is to detect discrepancies in these processes. Chow, A. Y. (2010). If any discrepancy is detected, the cell is prevented by these automatic checkpoints from proceeding to the next level pending the time when the discrepancy is corrected. This makes sure that the cell cycle goes on error-free.
Mutations are one of the types of genetic alterations that lead to development of cancer. These mutations define some certain oncogenes that are modified versions off the normal cellular protooncogenes. The products of protooncogenes are used in signal transduction pathways to promote cellular proliferation. Collins K et al (1997). However, the modified mutant versions of these protooncogenes (oncogenes) play a central role in the proliferation and perpetuation of cancer cells. Moreover the effect is such that mutation of only one gene will lead to transformation. Mutation can also cause the transformation of some cell types while not affecting other type of cells. For example, the Ras proteins are practically molecular switches that interchange between active and inactive states. The switch is turned on or off depending on the form of nucleotide to which it is associated. When the switch is on, the protooncogene leads to proliferation-stimulating signals. However, a mutation in the gene causes it to be in a permanently switched on position. Bernards R (2012). The result is that the cell enters a state of uncontrolled proliferation, leading to the formation of a cancer that grows uncontrollably.
Chromosomal translocation also occurs, leading to the formation of an oncogene, in which the end of one chromosome is fused with another chromosome, leading to the formation of a fusion protein. Example is the BCR/ABL in which the n-terminus of Bcr [breakpoint cluster region] and the C-terminus of the Abi [a regulator of proliferative signals] is fused. The result is called the Philadelphia chromosome. This leads to the Abi being permanently active, causing unregulated cell cycling. This chromosome is present in individuals that have Chronic Myelogenous leukemia. Bernards R (2012).
Furthermore, inherited cancer susceptibility is also caused by mutation in tumor suppressor genes. This can be either of two outcomes. it is either both copies of the tumor suppressor genes are mutated in which case the individual expresses phenotypic manifestation of the cancer or only one of the genes are mutated and the individual expresses the mutation in a heterozygous fashion and the individual only carries the mutation as a trait. The individual does not express the cancer phenotypically.
REFERENCES
Bernards R (2012). Cell Cycle regulation and Cancer. Accessed 28th January 2012 from http://streaming.cineca.it/sestri/courses/cancgen/Bernards.htm#top
Collins K, Jacks T and Paveletich N (1997). The Cell Cycle and Cancer. Proceedings of National Academy of Sciences of the United States of America. vol. 94 no. 7 2776-2778. Accessed 28th January 2012 from http://www.pnas.org/content/94/7/2776.full
Chow, A. Y. (2010) Cell Cycle Control by Oncogenes and Tumor Suppressors: Driving the Transformation of Normal Cells into Cancerous Cells. Nature Education 3(9):7 Accessed 28th January 2012 from http://www.nature.com/scitable/topicpage/cell-cycle-control-by-oncogenes-and-tumor-14191459
