Explain ‘Biochemical methylation’.
Answers
Methylation is a regulatory process that can prevent certain processes such as degradation or catalysis from occurring. In the restriction-modification system of bacteria, the bacterial DNA is methylated at adenine bases by methylase, thereby preventing the DNA from being degraded by restriction endonucleases. These restriction enzymes have active sites that recognize the specific amino acid-based conformations in DNA. The enzymes can bind and cleave the phosphodiester bonds of the backbone at recognized (cognate) DNA. Methylated groups lose one hydrogen bond linkage with the enzyme and thus decrease the binding energy, resulting in a lower enzyme affinity and no cleavage.
Methylation also occurs in amino acid synthesis and in gene expression. In the latter, cytosine is methylated at C5. This 5-methylcytosine interferes with the proteins that bind to start transcription. In amino acid synthesis, methylases and other methyl group carriers attach methyl groups.
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