This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
[{'content': 'True about DNA methylation \nSelect and explain. \nA. Alters gene expression, B. Genetic code remains intact, C. Role in Carcinogenesis, D. Protective mechanism against cleavage by restriction endonuclease', 'role': 'user'}, {'content': 'Answer: A \nExplanation: DNA methylation is an epigenetic mechanism used by cells to control gene expression. A number of mechanisms exist to control gene expression in eukaryotes, but DNA methylation is a commonly used epigenetic signaling tool that can fix genes in the "off" position.Methylation epigenetically modifies the function of the DNA. When located in a gene promoter, DNA methylation typically acts to repress gene transcription.', 'role': 'assistant'}]