DNA methylation and histone acetylation are epigenetic modifications of the DNA strands that bring about DNA stability and control gene expression. It is the addition of methyl and acetyl groups to the DNA and histone molecules, respectively. Find out more such differences between DNA methylation and histone acetylation in the table below.
DNA Methylation
DNA methylation is the process of the addition of methyl groups to the 5’ carbon of the cytosine rings in the DNA molecule. This addition mostly occurs at the CpG islands, meaning, at the cytosine bases that precede the guanine bases. The p here denotes the phosphodiester bond between them. These CpG islands are usually located in the promoter region, and methylation suppresses the activity of transcription. Methylation of cytosine residues is widespread and is seen commonly in both eukaryotes and prokaryotes.
However, adenine residues can also be methylated, but they are less studied. DNA methylation is an important procedure as it is associated with X chromosome inactivation, genomic imprinting, and some negative aspects such as ageing and carcinogenesis.
The process of methylation is assisted by the enzyme DNA methyltransferases (DNMT). In cancer development, the CpG islands get hypermethylated that resulting in the silencing of transcription and can give rise to oncogenes.
Histone Acetylation
Histone acetylation is an epigenetic modification in the lysine residues of the nucleosomes. The enzyme histone acetyltransferases (HAT) catalyse the reaction. Acetylation is the process of transfer of an acetyl group from acetyl coenzyme A to the N terminal of the lysine residues.
Refer: Histones & Importance Of DNA Packaging
Acetylation is important for gene regulation. The addition of acetyl groups removes positive charge from the histone molecules, this leads to less interaction between the N terminal of the histone and the phosphate group of the DNA. As a result, the chromatin condensation is relaxed, and which leads to a higher level of transcription in the genes. The chromatin can be condensed back by the process of deacetylation.
DNA Methylation vs Histone Methylation
| DNA Methylation | Histone Acetylation |
| Description | |
| The addition of a methyl group to the cytosine residue of the DNA molecule is referred to as DNA methylation. | The addition of acetyl groups to the lysine residues of the histone molecule is referred to as histone acetylation. |
| Location | |
| It takes place in the DNA molecules. | It takes place in the histone proteins. |
| Enzymes Involved | |
| DNA methyltransferase. | Histone acetyltransferase |
| Residues | |
| The cytosine residues get methylated. | The lysine residues get acetylated. |
| Importance | |
| DNA methylation is used to suppress the expression of genes. | Histone acetylation leads to relaxation of the chromatin and hence greater transcription. |
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Frequently Asked Questions
What is the difference between acetylation and methylation?
Acetylation is the process of the addition of acetyl molecules, whereas methylation is the process of the addition of methyl groups to the DNA molecule.
What is the difference between acetylation and methylation in terms of their effects on transcription?
DNA methylation helps in transcription regulation by suppressing or elevating the expression of genes, whereas histone acetylation leads to higher levels of transcription.
What is the function of histone deacetylase?
Histone deacetylase (HDAC) are enzymes that bring about deacetylation in the lysine residues of the histone molecule.
How DNA methylation affects gene expression?
DNA methylation alters gene expression. It usually suppresses the transcription of a gene.
Does DNA methylation increase or decrease transcription?
DNA methylation majorly decreases the level of transcription.
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