Summary
Addition of methyl groups to cytosine, usually silencing gene expression.
In depth
DNMTs add methyl groups to CpG cytosines; promoter CpG islands that are methylated are silenced. Methylation patterns are copied during replication by DNMT1 and altered in development and cancer.
It underlies imprinting and X inactivation.
In mammals, around 70 to 80 percent of CpG sites are methylated, except in CpG islands near active promoters. De novo methylation by DNMT3A and DNMT3B establishes patterns in the embryo, and TET enzymes remove marks via oxidation. Methylation is lost in two waves, in early embryos and in germ cells, and then reset.
In cancer, tumour suppressor promoters become hypermethylated while the overall genome is hypomethylated. Methylation patterns change with age and form epigenetic clocks that estimate biological age with high accuracy. Bisulfite sequencing reads methylation by converting unmethylated cytosine to uracil.
Remember: methylation of cytosine can cause mutations since methyl-C deaminates to thymine, so CpG sites are mutation hotspots.
Frequently asked questions
What is DNA Methylation?
Addition of methyl groups to cytosine, usually silencing gene expression.
Which area of biology covers DNA Methylation, and how advanced is it?
DNA Methylation is one of the 52 topics in Molecular Biology. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include DNA Repair, Histone Modification, Transcription Factors.
Can you give an example of DNA Methylation?
Tumour suppressor genes are often hypermethylated in cancers.
What should I learn before DNA Methylation?
Work through the Beginner topics in Molecular Biology first, such as Central Dogma, DNA Replication, Base Pairing, then return to DNA Methylation. Intermediate topics assume the Beginner vocabulary.
What topics are related to DNA Methylation?
The closest topics to DNA Methylation are DNA Repair, Histone Modification, Transcription Factors, Mutation and Repair Link. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand DNA Methylation?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for DNA Methylation. To practise the whole of Molecular Biology, use the Molecular Biology quiz.
How is DNA Methylation different from DNA Repair?
DNA Methylation: Addition of methyl groups to cytosine, usually silencing gene expression. DNA Repair: Mechanisms such as mismatch, excision and double-strand break repair that fix errors and damage in DNA. Read both side by side and note what each one explains.
How should I study DNA Methylation step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with DNA Repair and explain the difference aloud. Finally, take the Molecular Biology quiz and come back to this page for any question you miss.