HLTB22H3 Chapter Notes - Chapter 0: Genomic Imprinting, Non-Coding Rna, Histone Code
Document Summary
In mammals, dna methylation takes place after replication and during cell differentiation. Dna methylation involves the addition of a methyl group to cytosine. Dna methylation: a reaction catalyzed by a family of enzymes called dna methyl transferases(dnmts) Methylation takes place on cytosine bases located adjacent to a guanine base, this combination is called cpg dinucleotide. Many of these cpg nucleotides are located in places called regions called cpg islands, located in near promoter sequences adjacent to genes. Cpg islands and promoters are adjacent to essential genes and cell specific genes are unmethylated. Unmethylated genes make them more avialbe for transcription. Genes with adjacent methylated cpg islands and methylated promoters are transcriptionally silenced. The methyl groups in cpg dinucleotides occupy the major groove of dna and silence genes by blocking the binding transcription factors necessary to form transcription complexes. Methylation of cpg islands is a normal process during development.
