True about DNA methylation:
A i.e. Alters gene expression; B i.e. Genetic code remains intact; C i.e. Role in carcinogenesis and Protective mechanism against cleavage by restriction endonuclease DNA methylation alters the gene expression pattern in cells-for example it may cause X-chromosome inactivation, tumor suppressor gene silencing (in cancer cells)Q, suppression of expression of repetitive elements / deleterious elements / viral genes that have been incorporated into genome of host over time E. coli has 2 prominent DNA methylation system, both using S-adenosyl methionine (SAM) as a methyl group donor. Adenine or cytosine methylation in restriction - modification system, serves as a pa of defence mechanism against cleavage by restriction endonucleaseQ. I t helps the cell to distinguish its DNA from foreign DNA by marking its own DNA with methyl group and destroying (foreign) DNA without the methyl group. Mismatch repair mediated by Dam methylase improves the overall fidelity of DNA replication by fctor of 102 -103. Dam (DNA adenine Methylation) methylase, methylates adenosine residue to N6- methyl adenosine within the palindromic (51) GATC (3) sequence. This can serve to distinguish parent/template strand (which is methylated) from unmethylated (transient state) newly synthesized strand. So replication mismatch in vicinity of hemi-methylated GATC sequence are then repaired a/ t the information the methyated parent strand. In eukaryotic cells - 5% of cytidine in DNA are methylated to 5 Methyl cytidine. Methylation is most common it CpG islands (a C G rich region, upstream of promoter region and P signifies phosphodiester bond between them) producing methyl -CpG symmetrically on both strands of DNA.
Alters gene expression
Genetic code remains intact
Role in carcinogenesis and Protective mechanism against cleavage by restriction endonuclease both
All of the above