Cellular functions

As stated above, calcium is an extremely important cellular ion for several cellular functions. The concentration of calcium in human extracellular fluid is about 2.5 mM, while the intracellular concentration is only 100-200 nM depending on the cell type. Thus, there is 10 000-20 000 fold concentration difference between the cell interior and exterior that has to be maintained by cellular pumping mechanisms. This requires a large amount of energy. " ... 

The nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), are the chemical carriers of a cell s genetic information. Coded in a cell s DNA is the information that determines the nature of the cell, controls the cell s growth and division, and directs biosynthesis of the enzymes and other proteins required for cellular functions. 

The primary cellular function of mRNA is to direct biosynthesis of the thousands of diverse peptides and proteins required by an organism—perhaps 100,000 in a human. The mechanics of protein biosynthesis take place on ribosomes, small granular particles in the cytoplasm of a cell that consist of about 60% ribosomal RNA and 40% protein. 

FIGURE 3.10 Constitutive activity due to receptor overexpression visualization through binding and function, (a) Constitutive activity observed as receptor species ([RaG]/[RL0J) and cellular function ([RaG]/ ([RaG] + 3), where P = 0.03. Stimulus-response function ([RaG]/([RaG] + p)) shown in inset. The output of the [RaG] function becomes the input for the response function. Dotted line shows relative amounts of elevated receptor species and functional response at [R]/KG= 1. (b) Effects of an inverse agonist in a system with [R]/ Kq= 1 (see panel a) as observed through receptor binding and cellular function. 

Minimal and optimal criteria for experiments utilizing cellular function. 

The ankyrin repeat motif is one of the most common protein-protein interaction domains. Ankyrin repeats are modules of about 33 amino acids repeated in tandem. They are found in a large number of proteins with diverse cellular functions such as transcriptional regulators, signal transducers, cell-cycle regulators, and cytoskeletal proteins. 

Ca2+ is an important intracellular second messenger that controls cellular functions including muscle contraction in smooth and cardiac muscle. Ca2+ channel blockers inhibit depolarization-induced Ca2+ entry into muscle cells in the cardiovascular system causing a decrease in blood pressure, decreased cardiac contractility, and antiarrhythmic effects. Therefore, these drugs are used clinically to treat hypertension, myocardial ischemia, and cardiac arrhythmias. 

In higher organisms, calpain superfamily contains 16 independent genes that modulate cellular function. Out of them, 14 are Ca2+-dependent cysteine proteases. The other two encode smaller regulatory proteins that... 

Cyclic nucleotides (cAMP and cGMP) are formed enzymatically from the corresponding triphosphates. As ubiquitous second messengers, they mediate many cellular functions which are initiated by first (extracellular) messengers. Their prime targets in eucaryotic cells are protein kinases ( cyclic AMP-dependent protein kinase, cyclic GMP-dependent protein kinase), ion channels and ensymes. 

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. 

Other, more general effects of insulin on cellular function include stimulation of cell growth (increase in DNA and protein synthesis), inhibition of apoptosis, and modulation of ion-channel activity. 

Ly sophosphatidic acid (LPA) is the prototype of a group of bioactive lysophospholipids that act on specific G-protein-coupled receptors to mediate a wide variety of cellular functions. 

PKC isozymes are involved in a wide array of diverse cellular functions [5]. Most isozymes (e.g., PKC (3) are involved in proliferative responses, and hyperactivation with phorbol esters most typically results in cell growth and differentiation. However, isozymes can have opposing functions. PKC 8 is well-characterized as an apoptotic kinase, whereas the closely related PKC e is antiapoptotic. PKC also plays a key role in learning and memory. 

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. 

A small monomeric GTPase that regulates a number of cellular functions. 

Cellular functions are controlled by extracellular signals such as hormones, neurotransmitters, odorants, light and other chemical or physical stimuli. Only a few of these signal molecules, e.g., the highly lipid-soluble steroids or thyroid hormones, can diffiise across the... 

Thomas SM, Brugge JS (1997) Cellular functions regulated by Src family kinases. Annu Rev Cell Dev Biol 13 513-609... 

In concordance with the central role of ubiquitin modification in multiple cellular functions perturbations of this system are associated with a variety of diseases. Defects in the control of cell cycle regulators by the ubiquitin proteasome system are connected to cancer progression and many E3 ligases were originally identified as oncogenes. 

More recent analysis of tissue specific gene deletions showed that the Cav1.2 channel is involved in a wide variety of function including hippocampal learning, insulin secretion, intestine and bladder motility. Further analysis will be required to unravel the functional significance of voltage-dependent calcium channels for specific cellular functions. 

Chemical changes in the cellular environment include inactivation of cellular functions or the alteration of the chemical components of body fluid, such as a change in the pH. For example, antacids neutralize gastric acidity in patients with peptic ulcers. 

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