Final answer:
DNA methylation is an epigenetic process that adds a methyl group to DNA, commonly leading to reduced gene expression in eukaryotes by changing the chromosomal structure to a closed configuration, thereby decreasing accessibility for transcription.
Step-by-step explanation:
DNA methylation is a major method of eukaryotic transcriptional regulation. This refers to the addition of a methyl group to the DNA molecule, which is an epigenetic modification that leads to gene silencing. In eukaryotic cells, this process involves methylating certain cytosine nucleotides in DNA, commonly resulting in decreased levels of gene expression. Methylation patterns can be influenced by environmental factors and alongside histone modifications, such as acetylation and deacetylation, control the packaging state of DNA. These modifications affect the accessibility of DNA for transcription by influencing whether the DNA is in an open or closed chromosomal configuration. Eukaryotic transcription requires a variety of proteins and regulatory sequences to ensure specific gene expression, including the binding of transcription factors and RNA polymerase.
During chromatin remodeling, chemical modifications to histones and DNA signal to the cell to alter the chromosomal structure. This can include the addition of methyl groups through the activity of histone methyl transferases. Processes such as methylation and acetylation can make a chromosomal region more or less accessible for transcription by changing how tightly DNA is wound around histone proteins. Moreover, methylation patterns can be maintained through cell division, which makes these epigenetic changes partially heritable.