16.3 Eukaryotic Epigenetic Gene Regulation

16.3 Eukaryotic Epigenetic Gene Regulation

  • There is an animation about the workings of lac operon.
  • Eukaryotic gene expression is more complex than prokaryotic because the processes of transcription and translation are separate.
    • Eukaryotic cells can regulate gene expression at many different levels.
    • Epigenetic changes are inheritable changes in the expression of genes.
  • Control of access to the DNA is the beginning of otic gene expression.
    • There are two ways in which the access to the DNA can be controlled.
    • The way in which DNA is associated with histones can be changed.
    • There are genes that are associated with developmental changes and genes that are not.
  • The nucleus's DNA is wound, folded, and folded into chromosomes so that it can fit into the rest of the body.
    • Specific segments can be accessed by a specific cell type.
  • Histones package and order DNA into structural units called nucleosome complexes, which can be used to control access to the DNA regions.
    • Under the electron microscope, this winding of DNA around histone is like small beads on a string.
  • A nucleosome complexes are created by folded histone proteins.
    • The access to the underlying DNA is controlled by these nucleosomes.
    • The nucleosomes look like beads on a string when viewed through an electron microscope.
  • The beads can move along the string to expose different parts of the molecule.
    • Nucleosomes can move along DNA.
    • Gene expression is turned off when the nucleosomes are close together.
    • The DNA is exposed when the nucleosomes are far apart.
    • Gene expression can occur with the help of transcription factors.
    • Modifications to the histones affect the spacing of the nucleosomes.
  • One of the two X chromosomes is inactivated in females because of epigenetic changes.
  • The histone proteins and the DNA are regulated by signals on both of them.
    • These signals are added to histone and DNA to determine if a chromosomal region should be open or closed.
    • These tags can be added or removed as needed.
    • The histone "tails" at the N-terminus are home to some chemical groups.
    • The groups don't change the base sequence, but they do change how tightly wound the DNA is.
    • Changes in the charge of histones will affect how tightly wound the DNA molecule will be.
    • The charge becomes less positive and the binding of DNA to histones is relaxed by adding chemical modifications.
    • Altering the location of nucleosomes and the tightness of histone binding opens some regions and closes others.
  • The DNA molecule can be altered.
    • The CpG islands have very specific regions where DNA methylation occurs.
    • There are stretches with high frequencies of the two dinucleotides in the promoter regions of genes.
    • A methyl group can be added to the cytosine member.
    • The silenced genes may have other regulatory effects.
    • Some genes that are silenced during the development of the gametes of one parent are transmitted to the offspring.
    • The genes are said to be imprinted.
    • Maternal diet or other environmental conditions can affect the expression of genes.
    • The histone modifications of the genes appear to attract them.
    • Highly methylated and deacetylated histones are tightly coiled.
  • Histone and DNA can be modified.
    • Modifications affect the spacing and expression of genes.
  • Epigenetic changes can persist through multiple rounds of cell division and even cross generations.
    • The chromosomal structure can be altered as needed.
    • If a gene is silenced or turned off, the histone proteins and DNA have different modifications that signal a closed chromosomal configuration.
    • In this closed configuration, there is no access to the DNA for the transcription factors.