The Role of Epigenetic Events in Cancer Essay Example | Topics and Well Written Essays - 1000 words

The Role of Epigenetic Events in Cancer - Essay Example It is worth mentioning that most CpG sites have been lost from mammalian genomes during evolution, but in about 1% of human DNA consists of short areas where CpG sites have escaped depletion. Repetitive sequences of the human genome contain approximately 50% of all CpGs. Similar values are expected for other mammalian genomes. In contrast to CpG islands repetitive elements are thought to be constantly methylated. DNA methylation of most repetitive elements is maintained throughout development and even maintained during germ cell development. Methylated cytosines are more prone to fixate mutations compared with cytosine, C to T transitions occur frequently at methylated CpGs within repetitive elements. In consequence, this leads to an overall depletion of CpGs in repetitive elements and hence the bulk genome and an overall CpG deficit in mammalian genomes. CpG dinucleotide sequences are frequently the target of a chemical modification known as DNA methylation. The covalent modificatio n of the cytosine ring by a family of enzymes called DNA methyltransferases converts cytosines that are located 5 to guanosines to 5-methylcytosine. 5-methylcytosine has a propensity to undergo deamination to become uracil, which in turn becomes a thymidine during the next round of DNA replication if the deaminated base has not been repaired. The resulting C to T transition is mirrored by a corresponding G to A transition on the complementary DNA strand. As a result of methylation and subsequent deamination, CpG dinucleotide sequences have been progressively lost from the human genome over the course of many generations. Thus, the hypermutability of CpG sequences has led to a relative paucity of CpG sites in the human genome. The CpG dinucleotides that are the targets of DNA methyltransferases are distributed asymmetrically throughout the genome. Most regions of the genome have been depleted of CpG sites by spontaneous deamination.

Science Reported in Media vs. Scholarly Sources Research Paper

Science Reported in Media vs. Scholarly Sources - Research Paper Example the inner part of the eyelid can become so scarred in such a severe fashion that the whole eyelid could actually turn inwards and cause the lashes to rub on the eyeball which results in the scarring of the front part of the eye- the cornea. If this infection is not treated repeatedly and timely, this infection can even lead to the development of an irreversible corneal opacities and eventually even blindness. Trachoma is a rather common infection affecting a total of about 21.4 million people all over the world out of which some 2.2 million have become visually impaired and some 1.2 million are completely blind. The severity of this disease is clear from the fact that it was considered an epidemic and not only any infection outbreak. Trachoma is presently responsible for an overly large 3% of the total world’s blindness. This number however keeps varying because of socio-economic development effects and several different control programmes put in place for curbing the threat of this disease. In spite of several measures being placed, trachoma still widely carry its status of an hyper endemic in several of the extremely poor and very remote and poor rural areas in the continent of Asia, Africa, Australia, Central and South America and the Middle East. The patterns of active trachoma emerge majorly during the early adulthood and during middle-ages. In hyper endemic areas, trachoma is most common in children who ate attending preschool and the rates of prevalence of trachoma are as high as 60-90%. It like most diseased has the potential to majorly affect the most vulnerable members of the society and has a severe affect on children and women. Surprisingly, adult women as compared to men are at a huger risk of being affected by the complication that results in trachoma leading to eventual blindness. The major reason for this trend is that perhaps women spend greater amount of time with young children who are considered the major source of this heinous