Essay Example on Epigenetics environment and diseases









Epigenetics environment and diseases Introduction Epigenetics is the manipulation above genetics it is the study of changing heritable phenotypes as a result of modified gene expression but without altering the DNA sequences Chemical modifications on chromosome DNA and structures can change the pattern of gene expression All cells in the body except erythrocytes contain identical DNA sequences the epigenetics allows the cells to develop into specific ones by changing the gene expression pattern Functions of each type of cells are determined by the pattern and therefore by epigenetics Epigenome is changeable as different genes are required during different periods throughout life As the cells communicate with one another signals from inside the cell neighbouring cells and environment allows the cells to know when and how they should change Importance of signals are dependent on the stage of development For example at the start of embryonic division after fertilisation signals from neighbouring cells provide information of which cell types they should be develop into environmental signals influence more on the epigenome in later development stages Sperm and egg cells contain epigenetic signals or tags from each parent respectively 

These signals are erased after fertilisation which then allows the embryonic cells developed to have the ability to differentiate into any type of cells If the parental epigenetic signals were not erased these signals can conflict between chromosomes from each parent and the embryonic cells can not develop into required tissues and organs There are several mechanisms that regulate expression of genes and some of them are more well known Firstly DNA methylation silences the genes By adding methyl groups to the CpG motifs the genes can be turned off which unable RNA polymerase from expressing the genes During development cells can differentiate to be specific by turning off certain genes Stem cells can be produced by de methylation to turn all genes back on DNA are wrapped around proteins known as histones which have N terminal tails that can be acetylated and deacetylated Histone acetylation is processed by transferring the acetyl group form molecules such as acetyl coenzyme A to the lysine residues on the histone tails the reaction is catalysed by enzymes histone acetyltransferase HAT The deacetylation is catalysed by histone deacetylase HDAC and the acetyl is removed from the tail The histone acetylation loosen the DNA wrapped and deacetylation tightens it RNA polymerase can then climb on the loosened DNA to start transcribing genes Micrornas miRNA that are produced in the nucleus bind to mRNA that are being produced by ribosomes This binding blocks the ribosome and therefore stops translation of genes

While histone acetylation and deacetylation cause temporary alterations DNA methylation is known to be permanently silencing the transposable elements These regulatory mechanisms are essential as cell with all genes expressed will not function When fertilisation starts the DNA methylation rate in sperm cell is fast compared to the rate in the egg cell Both rate then drop until it reaches the blastocyst stage this is the point when the fertilised egg is ready for implantation and all DNA methylation signals are removed The cells in the blastocyst can now differentiate freely Mechanisms of how each cell goes down particular pathway remains unclear Once the embryo is formed all methylation tags are established Epigenetic memory directs the cell to go down a particular pathway without turning backwards the methylation pattern is maintained during cell division from generation to generation Identical twins share same genes however their physical appearance well beings may be extremely different if they grew up in different environments Therefore along with genetics direct and indirect external factors such as diet and life stress are also important factors towards the development of an organism throughout life An example is in bees Queen bees share identical genes with the worker bees however they develop ovaries and large abdomen as a result of being forced to be fed on royal jelly

These environmental factors can alter mechanisms that regulate gene expressions Environmental alterations to epigenetics can be beneficial or fatal Diseases such as cancer autoimmune disorders and mental disorders can be caused if gene expressions are altered DNA methylation DNA can be tagged by methyl groups Promoter DNA methylation is associated with silenced genes and it is important in maintaining cell types The process is carried out by DNA methyltransferases DNMT DNMT1 DNMT3a DNMT3b Embryonic development during fertilisation 3a and 3b are responsible for De Novo methylation differentiation allowing embryonic cells to develop into a cell type DNMT1 is for maintenance of methylation following differentiation and is active during cell division after differentiation Gene expression pattern and methylation pattern for each cell type is different Most CpG sites are methylated in humans but not the ones in promoter CpG island Promoter regions contain regulatory elements that control transcription of genes 3a and 3b obtain the methyl group from a molecule 

SAM the methyl group is added to the fifth carbon on cytosine and forming 5 methylcytosine DNMT flips cytosine 180 degrees out of the strand then the DNMT enzyme obtains the methyl group from SAM and transfer it onto cytosine finally the methylated cytosine is flipped back Human TET enzyme that regulate DNA methylation patterns It adds a hydroxyl group onto 5 methylcytosine and make it become 5 hydroxymethylcytosine TET can also convert 5 gydroxymethylcytosine back to cytosine through several pathways TET is therefore thought to be responsible for DNA de methylation Both DNA methylation and de methylation are tightly regulated in development by DNMT and TET in normal human cells during development but this balance is disrupted in cancer cell causes a change in DNA methylation pattern There are hypermethylation in promotor region and this is associated in tumour suppressor gene inactivation Cancer DNA also undergoes wide spread hypomethylation in the entire genome This type of regulation is found in every type of human tumour This methylation pattern can be used to detect cancer cells from normal cells

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