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.