Histones are alkaline proteins which play an important role in the packaging of DNA and the regulation of genes in eukaryotic organisms. Without histones, the unwound DNA in chromosomes would be very long, about 2 meters in length per cell. As a result, chromatin in the DNA is very tightly associated with these histone proteins, which package and order the DNA into structural units called nucleosomes. This supercoiled, condensed structure allows for the long DNA molecule to fit inside the nucleus. Selective winding and unwinding allows for portions of the DNA to be exposed. In this way, histones also play a role in regulating gene expression.
All Eukaryotes have five major classes of histones, each differing in molecular weight and amino acid composition. These classes are H1, H2A, H2B, H3, and H4. By using X-ray crystal structure, we are able to see that the bead on each nucleosome contains eight histone molecules, and two copies each of H2A, H2B, H3, and H4. This provides a repeating unit of about 200 base pair, of which 146 base pair are bound tightly around the eight-part histone core [1] and the remainder serves as linker DNA between nucleosome beads. The crystal structure deduced is shown below:
The eight histone proteins are shown in different colors, where blue represents H3, green represents H4, yellow represents H2A, and red represents H2B. The DNA double helix can be seen wound around the nucleosome core.
Besides the core histones, there also exists the linker histone, H1. This allows for multiple nucleosomes to be linked to each other. As a result, DNA is locked into place. Interestingly, histone H1 is very important in stabilizing chromatin higher-order structures, and 30-nanometer fibers form mo...
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As an inducer of HIF-1 production, it’s been used to study the apoptotic effects in HepG2 cells.
...plicates the identification of the loss of tumor suppressor gene (TSG) is epigenetic changes in the gene promoter. Hypomethylation of DNA and hyperacetylation of histones in the promoter region leads to successful transcription of the DNA. Therefore, any alteration in either of the two will disrupt the gene transcription.
Hall, Linley Erin. “Understanding Genetics DNA and RNA.” New York: The Rosen Publishing Group, Inc., 2011. Print. 01 Apr. 2014.
The nucleus contains genetic material that controls all the activities within a cell. A nucleus is made up of D...
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Chemistry dictates the structure of DNA. DNA is a polymer of monomers called nucleic acids. These are made of a nitrogenous base, a phosphate group and a sugar. It is the negative charge on the phosphate group that makes DNA an acid. There are 4 different bases: adenine, thymine, guanine and cytosine. In groups of three, these four bases can code for any protein coded for in an organism’s genome. Two strands of nucleic acids stack on top of each other in a double helix. The backbone of the nucleic acids consists of the interaction between phosphate groups and the hydroxide groups of nucleic acids. These are held together by covalent bonds called phosphodiester bonds. The helix itself is held together by hydrogen bonds. Although h...
To form a polynucleotide DNA, many nucleotides are linked together with 3`-5` phosphodiester linkages. In a compl...
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Precise chromosomal DNA replication during S phase of the cell cycle is a crucial factor in the proper maintenance of the genome from generation to generation. The current “once-per-cell-cycle” model of eukaryotic chromosome duplication describes a highly coordinated process by which temporally regulated replicon clusters are sequentially activated and subsequently united to form two semi-conserved copies of the genome. Replicon clusters, or replication domains, are comprised of individual replication units that are synchronously activated at predetermined points during S phase. Bi-directional replication within each replicon is initiated at periodic AT-rich origins along each chromosome. Origins are not characterized by any specific nucleotide sequence, but rather the spatial arrangement of origin replication complexes (ORCs). Given the duration of the S phase and replication fork rate, adjacent origins must be appropriately spaced to ensure the complete replication of each replicon. Chromatin arrangement by the nuclear matrix may be the underpinning factor responsible for ORC positioning. The six subunit ORC binds to origins of replication in an ATP-dependent manner during late telophase and early G1. In yeast, each replication domain simply contains a single ORC binding site. However, more complex origins are characterized by an initiation zone where DNA synthesis may begin at numerous locations. A single round of DNA synthesis at each activated origin is achieved by “lic...
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A specialized cellular molecule copies a given sequence of DNA whose end product will contribute to its function. DNA is a long molecule that usually can be found in a condensed state. Specialized types of proteins called histones wrap the DNA, forming nucleosomes, and thus occupying a smaller volume in the nucleus. There are 2 types of nucleosomes, their importance being in that they tell what will be expressed or not. Euchromat...
A recent field of biology, called epigenetics, is rapidly transforming previous ideas on the impact of genes. The...
Histopathology and molecular pathology both fall within the medical science branch of pathology where the primary concern is the examination of tissues, body fluids, and organs to aid in the diagnosis of diseases.