Heterochromatin is a tightly packed DNA region where genes in such regions are usually not transcribed. Numerous transposable elements (TEs) and repetitive DNA are found in heterochromatic regions. As they can transpose along the genome and disrupt gene functions, it is essential to repress such TEs and DNA repeats (Lippman et al., 2004).
Heterochromatin is able to maintain internucleosomal interactions as well as chromatin fiber interactions between cis-elements. It can be passed on to subsequent generations and can control gene expressions by inhibiting transcription epigenetically, a process known as silencing. Heterochromatin is able to suppress recombination between interspersed DNA repeats. This prevents non-homologous recombination, which may result in copy number variations in gene clusters and give rise to genetic diseases.
In flowering plants like Arabidopsis (which will mainly be the focus of this essay), cytosine methylation is abundant in heterochromatic regions, and plays an important role in epigenetic regulation of genomes. DNA methylation in such genomes can affect cytosine residues in 3 different contexts: CG, CHG and CHH, where H can be C, T or A. One can wonder how these methylations are maintained in plant genomes. This can be explained by the dimethylation activity of cytosine-DNA methyltransferases on histone H3 at lysine 9(H3K9).
DNA methylation is initiated by RNA-directed methylation (RdDM), a process which is led by small and long non-coding RNAs via the Dicer-Argonaute pathway (Dinh et al., 2013). Once DNA methylation is initiated, it must be maintained to effectively suppress gene transcription in heterochromatin.
Cytosine-DNA methytransferases are enzymes that introduce a methyl group to cytosi...
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Histone modification may or may not be dependent on DNA methylation and is difficult to detect compared to LOH.
In humans and other eukaryotes, there is an extra step. RNA polymerase can attach to the promoter only with the help of proteins called basal (general) transcription factors. They are part of the cell's core transcription toolkit, needed for the transcription of any
DNA methylation is catalyzed by the enzyme: DNA methyl trasnferase (DNMTs). Methylation of DNA segments leads to the silencing of transposable elements. Hence this mechanism is repressive to transcription, by that enhancing genomic stability. However, there exist “CpG” islands that are associated with gene promoters that escape methylation hence stability.
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... starts relaxing the supercoils and altering of DNA and interacts with DNA helicase SGS1 and plays a role in DNA recombination, also cellular aging and maintenance of genome stability. Alternate splicing results in multiple transcript variants. Additional spliced variants of the gene have been described, but their complete length is unknown.
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...
By utilizing, and, if possible, modifying this special DNA structure, one may see a reduction of age related illness, diseases, and signs of aging. In this review of human telomeres, we will discuss the roles and functions of the telomere, its structure, and the relation of telomere length to aging and tumorigenesis. Role and Functions of The Telomeres Telomeres are special DNA structures that consist of repetitive nucleotide sequences, which serve as a “cap” to protect the ends of the chromosomes. These repetitive sequences can range from thousands of base pairs in Vertebrates to about a few hundreds of base pairs in yeast cells (Oeseburg, et al. 2009). The 'Secondary' of the 'Secondary' of the 'Secondary' of the 'Secondary' of the 'Secondary' of the 'Secondary' of the 'Secondary' of the 'Secondary' of the 'Secondary' of the 'S Located at the ends of the chromosomes, the telomeres serve as a biological life line for cells.
With plants of the genus Brassica importance in the form of vegetables and oilseeds (Wang and Freeling 2013), the results of this experiment offer a view into their inheritance patterns which can in the long term be replicated for different outcomes. Augustine et al. discuss the importance of these plants’ traits in terms of food production by stating that studying the mutations of Brassica may lead to improvement of crops by expressing mutations that are desirable phenotypic traits (2014). Brassica are an important part of the global food supply and if any plants can be genetically altered by selective fertilization then those steps should be taken to produce larger, more efficient, or shorter cycling plants. This experiment has supported the inheritance of traits according to Mendel by examining the inheritance of anthocyanin in B. rapa.
A chromosome is made up of two identical structures called chromatids. The process of nuclear division is called interphase; each DNA molecule in a nucleus makes an identical copy of itself. Each copy is contained in the chromatid and a characteristic narrow region called the centromere holds the two chromatids together. The centromere can be found anywhere along a chromosome but the position is the characteristic for a particular chromosome. Each Chromatid contains one DNA molecule. DNA is the molecule of inheritance and is made up of a series of genes. The fact that the two DNA molecules in the sister chromatids, and hence their genes, are identical is the key to precise nuclear division.
Campbell N. A., Reece L. A., Cain M. L., Wasserman S. A., Minorsky P. V. and Jackson R. B. (2008). Regulation of Gene Expression
Inside the cells that produce sperm and eggs, chromosomes become paired. While they are pressed together, the chromosomes may break, and each may swap a portion of its genetic material for the matching portion from its mate. This form of recombination is called crossing-over. When the chromosomes glue themselves back together and separate, each has picked up new genetic material from the other. The constellation of physical characteristics it determines is now different than before crossing-over.
A recent field of biology, called epigenetics, is rapidly transforming previous ideas on the impact of genes. The...
Discoveries in DNA, cell biology, evolution, and biotechnology have been among the major achievements in biology over the past 200 years with accelerated discoveries and insight’s over the last 50 years. Consider the progress we have made in these areas of human knowledge. Present at least three of the discoveries you find to be the most important and describe their significance to society, heath, and the culture of modern life.