What are the common types of epigenetic modifications? Describe how epigenetic modifications can ...

Epigenetic modifications consist of the addition and removal of chemical groups such as methyl groups (methylation and demethylation), acetyl groups (acetylation and deacetylation),
and phosphate groups (phosphorylation and dephosphorylation) near the amino-terminal
(N-terminal) ends of histone proteins. These epigenetic marks alter how tightly DNA and nucleosomes bind together. The tighter the association, the less likely it is that transcription will occur; conversely, looser association between nucleosomes and DNA increases transcription. Methylation of nucleosome N-terminal tails often leads to tighter packaging of chromatin and reduces transcription, whereas acetylation of histone tails loosens chromatin and leads to more transcription. Phosphorylation is detected in both more compact and less compact chromatin. Epigenetic modifications alter the strength of association between nucleosomes and DNA and
can lead to the displacement of nucleosomes (i.e., to remodeling of chromatin) to make regulatory DNA sequences more accessible to DNA-binding proteins.