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Naturally Occurring Polymers—Animals
Published in Charles E. Carraher, Carraher's Polymer Chemistry, 2017
The most important group of transposons is believed to be the long interspersed element or LINE groupings (there are three LINE families with only the LINE1 family active) that encodes instructions for whatever it needs, including copying its DNA into RNA, and copying the RNA back again into the DNA, and finally moving out of and into the chromosome. LINEs are only about 6000 base pairs in length (6 kb). Interestingly, most of these LINEs are found in the C- and G-rich or gene-poor regions of the genome. The LINEs have other “parasites” accompanying them called Alu elements that are only about 300 base pairs long and these sequences are the most abundant sequences in our genome. (They are given the name Alu because their sequence generally includes one copy of the recognition sequence for the restriction endonuclease AluI.) While Alu elements cannot replicate on their own, they “borrow” the needed hardware from the LINE segments to reproduce. Because of their active nature, they can cause trouble. For instance, in the development of an egg or sperm cell, a replicating Alu segment can be inserted, resulting in a child with a genetic disease. But Alu segments do perform positive functions. They become activated, helping modulate the body's response when the body is exposed to stresses such as sudden changes in temperature and light and exposure to alcohol. Alu segments are found only in the higher primates and are responsive to a large family of receptor proteins that allow cells to recognize potent hormones such as estrogen, retinoic acid, and thyroid hormone. Their presence appears to allow the surrounding site to be more flexible and to slightly change in shape when exposed to these hormone and hormone-like chemical agents.
Epigenotoxicity: a danger to the future life
Published in Journal of Environmental Science and Health, Part A, 2023
Farzaneh Kefayati, Atoosa Karimi Babaahmadi, Taraneh Mousavi, Mahshid Hodjat, Mohammad Abdollahi
The International Agency for Research on Cancer (IARC) considers foreign exhaust emissions of gasoline engines carcinogenic to humans. Among the gasoline components, benzene is of particular importance as it is a potent carcinogen to humans. Evidence and in vivo studies on human blood suggested that benzene-induced epigenetic changes may contribute to leukemogenesis and acute myelogenous leukemia (AML). Alu elements are involved in the evolution and are considered genetic markers. These elements are a short range of DNA evolved from the small cytoplasmic 7SL RNA.[23] Increased Urinary benzene (BEN-U) raises Alu-Y and Alu-J expression and hypomethylation of the L1-Pa5 repetitive element gene.[24] Besides, benzene may cause methylation of H3K9. Global DNA hypomethylation in human TK6 lymphoblastoid cells is caused by the oxidized metabolite of benzene.[24,25] Hydroquinone (HQ), the major benzene metabolite, with the FAS-AS1 and DNMT3b lncRNA complex regulates FAS gene expression through histone acetylation in TK6 immune cells, which is one of the causes of leukemogenic.[26] In today’s oil industry, due to the widespread use of chemicals and their presence in the environment from non-oil sources, human exposure to benzene is inevitable, and possible chronic adverse health effects are related. In a study of normal liver cells, benzene and its metabolites alter global DNA methylation by altering DNA methyltransferase activity.