Glossary
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  • 5

  • 5-methylcytosine
    DNA methylation usually occurs in mammals on the DNA base cytosine (C).
  • a

  • Acetylation
    An epigenetic mark that usually leads to activation of a gene.
  • Acetyltransferases
    A group of enzymes that catalyze the addition of an acetyl group onto a histone. Likely increases gene expression.
  • c

  • Chromatin
    The complex of DNA, histones, RNA, and other proteins that comprise the structural basis of chromosomes.
  • CpG site
    A region in DNA where cytosine and guanine appear consecutively; methylation can occur here.
  • d

  • DNA methylation
    The addition of a methyl group directly to the DNA leads to the silencing or shutting off of a gene.
  • DNA methyltransferases
    Enzymes that catalyze the transfer of a methyl group onto DNA. Likely reduces gene expression.
  • e

  • Epiallele
    Variations in the epigenetic status of a gene or region of the genome.
  • Euchromatin
    A loosely packed form of chromatin that can be actively transcribed as it is more accessible for transcription.
  • h

  • Heterochromatin
    A tightly packed form of chromatin that is likely not being actively transcribed because the DNA is less accessible for transcription.
  • Histone
    In eukaryotic cells, histones package and order the DNA into structural units called nucleosomes. They are the chief protein components of chromatin, and act as spools around which DNA winds.
  • Histone acetyltransferase
    Enzymes that add acetyl groups to histones at specific lysine residues. Generally increases gene expression.
  • Histone deacetylase
    Enzyme that remove acetyl groups from N(6)-acetyl-lysine residues on a histone.
  • Histone methyltransferase
    A class of enzymes that adds methyl groups to histones.
  • Histone modification
    Histones can be tagged with various molecules that can influence whether DNA is tightly (leading to a decrease in gene expression) or loosely (leading to an increase in gene expression) wound.
  • Hypermethylation
    A region of DNA with very high levels of methylation. Indicates low gene activity.
  • Hypomethylation
    A region of DNA with very low levels of methylation. Indicates high gene activity.
  • m

  • microRNA
    Small RNA molecules that regulate gene expression by blocking translation of a messenger-RNA molecule.
  • n

  • non-coding RNA
    RNA molecules which are not transcribed into proteins. Their function is to regulate gene expression at the transcriptional and post-transcriptional level.
  • Nucleosome
    The structural unit of a eukaryotic chromosome, consisting of a length of DNA coiled around a core of histones.
  • u

  • Ubiquitination
    The addition of an ubiquitin molecule to a protein. This event can signal for a protein's degradation, alter its cellular location, affect their activity, and promote or prevent protein interactions.
  • x

  • X-inactivation
    When one of the two X-chromosomes in the cells of female mammals is epigenetically silenced.