Genetic Changes that Result in Cancer

Hereditary and nonhereditary forms of colon cancer exist. Nonhereditary cancers involve mutations that are said to arise spontaneously, and these mutations are called somatic mutations. Hereditary cancers involve mutations that are called germline mutations. Hereditary cancers are much less common than spontaneous 

Mutations in p53 occur in spontaneous and inherited cancers. The role of p53 in DNA repair appears to be to momentarily halt the progression of the cell cycle, so as to give various DNA repair enzymes a chance to complete their job, prior to initiation of DNA synthesis. Overall, p53 is mutated in about half of all human cancers. Li-Fraumeni syndrome is a rare type of cancer that involves an inherited mutation in p53. About 50% of the affected persons acquire cancer by the age of 30 (Harvey et ah, 1995). 

RAS is a component of a signaling pathway, and is involved in regulating the rate of the cell s division. RAS is mutated in about 20% of all human cancers. Specific genetic diseases resulting in mutations of RAS and of cadherin seem not yet to have been identified. 

Most of the mutations in human APC have been found to result in the conversion of CGA (cytosine-guanine-adenine), which codes for arginine, to TGA (thymine-guanine-adenine), which is a stop codon (Polakis, 1997). The stop codons in m A (UAA, UAG, and UGA) act as a signal during translation that halts polypeptide formation at that point. The result is synthesis of a truncated polypeptide. All t)rpes of mRNA contain stop codons however, if a mutation results in the appearance of a stop codon in a new location, then transcription will stop at that new location. 

The body s goal of these enzyme-catalyzed reactions is not to cause mutations or cancer, but only to modify the heterocyclic amines to forms that are more water soluble and more readily excreted in the urine. Most of the heterocyclic amines that bear acetyl groups or sulfate groups are promptly excreted. However, a minority react with small molecules and macromolecules in the cell. 

Possible Correlation betiveen Gene Mutation and Cell Behiioior 

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Genetic Changes that Result in Cancer 897 Complete Repair of U G and T G Mismatches... 

A breakdown product of ptaquiloside has been shown to react with DNA, with the result that the DNA chain breaks. The ptaquiloside breakdown product reacts specifically with adenine, one of the four bases that form the code in the DNA molecule. The loss of this base from the DNA and the change in the DNA structure can cause mutations by altering the reading of the base pair code. Such genetic changes and mutations can lead to cancer. 

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