Histone are proteins which the chromatin wraps round to be packaged and therefore silence the transcription of the DNA. Histone modifications affect how tightly bound the DNA is to the histone, and depending on these modifications the level of silencing is affected. The enzymes …show more content…
The first two enzymes are DNA Methyl Transferase 3a and 3b (DNMT 3a and 3b), these two establish the methylation of the CpG islands for the first time. Then once the methylation has been established, DNMT1 maintains these methyl groups on the DNA during the DNA replication (Tollefsbol, 2010).
DMNT enzymes add methyl groups to the DNA by binding to the DNA, they then effectively turn the DNA double helix inside out exposing the base pairs, this is called ‘base flipping’, once the cytosine is exposed, a cysteine is used to nucleophilically attack the sixth carbon of the cytosine (C6), this transfers a methyl group from another molecule S-adenosyl-I-methionine, to the fifth carbon on the cytosine (C5), this creates 5-methyl cytosine (Zhang and Bruice,