Cell/cellular function/processes

A process in which a substance gains entry into a cell. Endocytic mechanisms are crucial for a variety of cellular functions such as the uptake of nutrients, regulation of cell surface expression of receptors, maintenance of cell polarity, and more. Receptor-mediated endocytosis via clathrin-coated pits is the most studied endocytic process, which is important for regulation of the time and magnitude of signals generated by a variety of cell-surface receptors. 

Proteosomal degration is the process by which improperly folded proteins or proteins with altered post-translational modifications are removed from a cell before they have a detrimental effect on cellular function. This is performed in small organelles known as proteosomes. Proteins are targeted for destruction in the proteosome by having a number of small ubiquitin molecules added. 

Both the heat and cold shock response are universal and have been studied extensively. The major heat shock proteins (HSPs) are highly conserved. They are involved in the homeostatic adaptation of cells to harsh environmental conditions. Some act as molecular chaperones for protein folding, while others are involved in the processing of denatured polypeptides whose accumulation would be deleterious. The cold shock results in the transient induction of cold shock proteins (CSPs), which include a family of small acidic proteins carrying the cold shock domain. The CSPs appear to be involved in various cellular functions such as transcription, translation and DNA recombination. 

Changes in membrane structure (eg caused by ischemia) can affect water balance and ion flux and therefore every process within the cell. Specific deficiencies or alterations of certain membrane components lead to a variety of diseases (see Table 41-5). In short, normal cellular function depends on normal membranes. 

Nearly all cellular functions are determined by the activity of proteins. Proteins act as catalysts, receptors or structural components that are required for the life of a cell. Many cellular processes are performed by complexes of several different proteins. It is essential that the protein components of these complexes be expressed at the same time and in the same place for the cell to function efficiently. Therefore, an understanding of cellular function at the molecular level requires knowledge of the patterns of expression of all of the component proteins. 

The most common second messenger activated by protein/peptide hormones and catecholamines is cyclic adenosine monophosphate (cAMP). The pathway by which cAMP is formed and alters cellular function is illustrated in Figure 10.1. The process begins when the hormone binds to its receptor. These receptors are quite large and span the plasma membrane. On the cytoplasmic surface of the membrane, the receptor is associated with a G protein that serves as the transducer molecule. In other words, the G protein acts as an intermediary between the receptor and the second messengers that will alter cellular activity. These proteins are referred to as G proteins because they bind with guanosine nucleotides. In an unstimulated cell, the inactive G protein binds guanosine diphosphate (GDP). When the hormone... 

Tissues consist of smaller repeating units on the scale of hundreds of micrometers in vivo. The 3D architecture of these repeating tissue units underlies the coordination of multicellular processes, emergent mechanical properties, and integration with other organ systems via the microcirculation [11], Furthermore, the local cellular environment presents biochemical, cellular, and physical stimuli that orchestrate cellular fate processes such as proliferation, differentiation, migration, and apoptosis. Thus, successful fabrication of a fully functional tissue must include both an appropriate environment for cell viability and function at the microscale... 

Oxidized LDL alter cellular functions role in cell death Oxidized LDL seem to be poorly degraded by lysosomal enzymes and accumulate in lysosomes altering in turn their functionality (Dean et al., 1997). It has been proposed that inhibition of oxidized LDL degradation and subsequent lipid accumulation may induce a destabilization of the acidic compartment, and lysosomal rupture with a relocation of lysosomal enzymes in the cytosol (li W et al, 1998). This process, also called endopepsis , occurs early and could precede mitochondrial dysfunction and cell death (Lossel et al., 1994). Moreover, oxidized LDL trigger a dysfunction of the intracellular proteolytic ubiquitin/proteasome pathway (early activation followed by inhibition)... 

PARP-1 is an abundant ( 1 to 2 million molecules per cell) and ubiquitous nuclear protein that plays important roles in a variety of cellular functions. One aspect of PARP-1 biology is the modulation of chromatin structure through direct nucleosome binding, covalent modification of chromatin proteins, or the production of PAR which can serve as a polyanionic matrix for the binding of chromatin proteins. Given its role in a variety of physiological and pathophysiological processes, PARP-1 has... 

Cell cycle progression, apoptosis, DNA damage and DNA repair are cellular functions that are regulated by several mechanisms. One such important regulatory mechanism is posttranslational modification of histone and non-histone proteins. Myriad of reports have been shown that acetylation of non-histone proteins apart from histones, contributes in major to these processes. 

By revealing the identity of a spectrum of molecules involved in different cellular functions, such results provide a means for mechanistic speculation and the subsequent development of neuroprotective strategies. Results such as these are now commonly used as a reference for predicting the functions of cells under given conditions and in assigning putative biological process aimotation to unknown genes. 

Since the discovery of the first histone demethylase in 2004, a number of demethy-lases have been identified and implicated in the control of gene expression programs and cell fate decisions. The cellular functions of histone demethylases are only beginning to be deciphered, but many of these enzymes have nevertheless been found to play biologically important roles. Histone demethylases are linked to the regulation of for example stem cell self-renewal, differentiation, proliferation and hormone-dependent responses. These processes are critical for development and cellular homeostasis and their deregulation is implicated in pathological disorders. 

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