The Cell Nucleus

Section 28 9 Within the cell nucleus double helical DNA adopts a supercoiled terti ary structure m which short sections are wound around proteins called histones This reduces the effective length of the DNA and maintains it m an ordered arrangement... 

Ara-A is phosphorylated in mammalian cells to ara-AMP by adenosine kinase and deoxycytidine kinase. Further phosphorylation to the di- and triphosphates, ara-ADP and ara-ATP, also occurs. In HSV-1 infected cells, ara-A also is converted to ara-ATP. Levels of ara-ATP correlate directly with HSV rephcation. It has recently been suggested that ara-A also may exhibit an antiviral effect against adenovims by inhibiting polyadenylation of viral messenger RNA (mRNA), which may then inhibit the proper transport of the viral mRNA from the cell nucleus. 

Proteins are complex molecules that give cells structure and act as both enzymes and motors within cells. Proteins are long strings of amino acids folded in specific three-dimensional formations. There are twenty different animo acids in our bodies. DNA, the genetic material located in the cell nucleus, carries information for the order of the amino acids in each protein. Indeed, in the simplest sense, a gene is the... 

I Replication—the process by which identical copies of DNA are made so that information can be preserved and handed down to offspring I Transcription-—the process by which the genetic messages are read and carried out of the cell nucleus to ribosomes, where protein synthesis occurs... 

Vivi-s, E., Brodin, P., and Lebleu, B. A truncated HIV-1 Tat protein basic domain rapidly translocates through the plasma membrane and accumulates in the cell nucleus. J. Biol. Chem. 1997, 272, 16010-16017. 

At its most fundamental level, the circadian cycle rests on the influence of so-called clock genes . These genes have been studied most extensively in insects but they have also been found in humans. Their protein products enter the cell nucleus and regulate their own transcription. This feedback process is linked to exposure to light and so it is not surprising that visual inputs are important for maintenance of circadian rhythms. However, it is not the reception of specific visual information, transmitted in the optic nerve to the lateral geniculate nucleus (LGN) and visual cortex (i.e. visual discrimination), that is responsible for the rhythm but the more simple, almost subconscious, reception of light. 

One goal of our current investigation is to show that genetically important cellular constituents can initiate the release of an alkylating agent from the N-nitrosamide. This might explain how highly reactive diazohydroxide metabolites effect the alkylation of nucleic acids within the cell nucleus. Preliminary evidence ( ) summarised in Table II shows that the decomposition of... 

Biolistics involves bombarding plant cells with tiny (4- am) microprojectiles made of gold or tungsten. These microprojectiles are coated with DNA and are propelled at high velocity from a particle gun or gene gun into plant tissue or cells. In this method, the projectile penetrates the cell wall and carries the transgene into the cell nucleus. 

An important consideration for DNA CT in the cell is the dramatically different environment of the DNA molecule in vivo. Unlike the naked DNA typically used in our in vitro assemblies, cellular DNA is intimately associated with proteins, packaged into chromosomes, and stored in the cell nucleus. Several experimental investigations demonstrate definitively that proteins can both modulate and participate in CT reaction in DNA. 

The binding of a hormone to its receptor initiates intracellular events that direct the hormone s action. Ultimately, all hormones produce their effects by altering intracellular protein activity. However, the mechanism by which this occurs depends on the location of the hormone receptor. Receptors are typically located on the cell surface or in the cell nucleus. As a result, most hormones carry out their effects by means of two general mechanisms ... 

The eukaryotes these include animals, plants, fungi and protozoa, the DNA of which is enclosed in a membrane-enclosed organelle (the cell nucleus). They have a cytoskeleton (a fine membrane-like network in the interior of the cell, which provides stability) and contain mitochondria. Higher plants, as well as algae, are equipped with chloroplasts for photosynthesis. 

Fig. 1.11 Applications of LDHs as (A) non-viral vector in gene therapy for transfection of DNA to the cell nucleus, and (B) as matrix for enzymes immobilization in the development of biosensors.

Zanta MA, Belguise VP, Behr JP (1999) Gene delivery a single nuclear localization signal peptide is sufficient to carry DNA to the cell nucleus. Proc Natl Acad Sci USA 96 91-96... 

To perform its unique functional role each neuron must regulate a host of intracellular activities, that occur in axons and dendrites distant from the cell nucleus. For example, axonal guidance during development, or remodeling of dendritic spines in response to local input, each involves many different complex control systems that are highly localized and largely autonomous. [ 1 ]. 

Sensitivity of cancerous cells to copper may reflect cell DNA content. Two closely related rat hepatoma cell lines differed in sensitivity to copper toxicity by a factor of four DNA content in each cell line decreased with increasing copper concentrations, but at different rates. Severity of toxicity was associated with increasing accumulations of copper in the cell nucleus and with decreasing DNA (Toussaint and Nederbragt 1993). 

Only 2% of total plasma testosterone is present in the active unbound state that penetrates the prostate cell, where it is converted to DHT by 5 a-reductase. DHT subsequently binds with a cytoplasmic receptor and is transported to the cell nucleus where transcription and translation of stored genetic material occur. 

Simultaneously, Gorski s group (Welshons et al. 1984), utilizing a type of cell fractionation that permits separating the cytoplasm from the nucleus, was also able to detect the presence of nuclear ER, even if the cell had not been exposed to hormones. These findings led to a different theoretical formulation, according to which the native receptors would be found in the cell nucleus, to which the hormone would accede directly. 

In the absence of hormone, the three-dimensional configuration of the receptor favors binding to corepressors present in the cell nucleus. The interaction is produced at the level of zipper-type sequences of leucines (-L-X-X-L-), present in the corepressors, with the LBD of the receptor. This has a structure that is complementary to the leucine zipper, which remains accessible while the receptor itself does not bind to the hormone (Gruber et al. 2002 Nilsson et al. 2001). 

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