Hormone cellular specificity

In minute amounts, hormones engender specific biochemical primary reactions through cellular metabolic processes, which subsequently trigger secondary reactions through physiological processes. 

CELLULAR SPECIFICITY FOR THE EFFECTS OF THYROID HORMONE AND NGF IN THE BRAIN... 

In spite of its appeal, the hormone gene theory leaves many questions unanswered. First, it remains to be established that the effects on the genome and protein synthesis are primary and not secondary to subtle changes in other cellular mechanisms. Second, the selectivity of the hormone to specific target cells, specific chromosomes, and specific sites within the chromosome must be elucidated. And, third, there is no information on the molecular interaction between the genome and the hormone. 

With the mounting evidence for subcellular hormone receptor sites and evidence for tissue and sometimes cellular specificity of certain plant hormone effects, it seems clear that the resolution of fundamental problems associated with plant growth and development will require an understanding of the processes of expansion, division, and differentiation at the cellular level. Nevertheless, it is often necessary and sometimes easier to study these processes as they occur in complex tissues. In this chapter the emphasis will be on the hormonal regulation of cell development, while recognizing that the processes involved are strongly influenced by both the physical constraints and metabolic activities of neighboring cells in complex tissues. 

Finally, certain membrane proteins act as cellular specific receptors. They permit the yeast to react to various external stimuli such as sexual hormones or changes in the concentration of external nutrients. The activation of these membrane proteins triggers the liberation of compounds such as cyclic adenosine monophosphate (cAMP) in the cytoplasm. These compounds serve as secondary messengers which set off other intercellular reactions. The consequences of these cellular mechanisms in the alcoholic fermentation process merit further study. 

Polypeptide hormones are synthesized as part of a larger precursor molecule or prohormone. Cleavage of the prohormone by specific cellular enzymes, ie, peptidases, produces the secreted form of the hormone. In some cases, multiple bioactive hormones are produced from a single prohormone. 

AKAPs are a diverse family of about 75 scaffolding proteins. They are defined by the presence of a structurally conserved protein kinase A (PKA)-binding domain. AKAPs tether PKA and other signalling proteins to cellular compartments and thereby limit and integrate cellular signalling processes at specific sites. This compartmentalization of signalling by AKAPs contributes to the specificity of a cellular response to a given external stimulus (e.g. a particular hormone or neurotransmitter). 

A sequence stretch 300 base pairs upstream of the transcriptional start site suffices for most of the transcriptional regulation of the IL-6 gene (Fig. 1). Within this sequence stretch several transcription factors find their specific recognition sites. In 5 to 3 direction, AP-1, CREB, C/EBP 3/NF-IL6, SP-1 and NF-kB can bind to the promoter followed by TATA and its TATA binding protein TBP. Most enhancer factors become active in response to one or several different stimuli and the active factors can trigger transcription individually or in concert. For example, AP-1 is active upon cellular stress, or upon stimuli that tell cells to proliferate CREB becomes also active if cells experience growth signals, but also upon elevation of intracellular levels of cyclic adenosine monophosphate (cAMP), which occurs upon stimulation if so called hormone-activated G protein-coupled receptors. 

Phosphorylation by protein kinases of specific seryl, threonyl, or tyrosyl residues—and subsequent dephosphorylation by protein phosphatases—regulates the activity of many human enzymes. The protein kinases and phosphatases that participate in regulatory cascades which respond to hormonal or second messenger signals constimte a bio-organic computer that can process and integrate complex environmental information to produce an appropriate and comprehensive cellular response. 

Cellular Carriers. Erythrocytes, leukocytes, platelets, islets, hepatocytes, and fibroblasts have all been suggested as potential carriers for drugs and biological substances. They can be used to provide slow release of entrapped drugs in the circulatory system, to deliver drugs to a specific site in the body, as cellular transplants to provide missing enzymes and hormones (in... 

Generally, a single hormone does not affect all of the body s cells. The tissues that respond to a hormone are referred to as the target tissues. The cells of these tissues possess specific receptors to which the hormone binds. This receptor binding then elicits a series of events that influences cellular activities. 

The cAMP molecule serves as the second messenger, which carries out the effects of the hormone inside the cell. The primary function of cAMP is to activate protein kinase A. This kinase then attaches phosphate groups to specific enzymatic proteins in the cytoplasm. The phosphorylation of these enzymes enhances or inhibits their activity, resulting in the enhancement or inhibition of specific cellular reactions and processes. Either way, cellular... 

In mammals, as in yeast, several different metallothionein isoforms are known, each with a particular tissue distribution (Vasak and Hasler, 2000). Their synthesis is regulated at the level of transcription not only by copper (as well as the other divalent metal ions cadmium, mercury and zinc) but also by hormones, notably steroid hormones, that affect cellular differentiation. Intracellular copper accumulates in metallothionein in copper overload diseases, such as Wilson s disease, forming two distinct molecular forms one with 12 Cu(I) equivalents bound, in which all 20 thiolate ligands of the protein participate in metal binding the other with eight Cu(I)/ metallothionein a molecules, with between 12-14 cysteines involved in Cu(I) coordination (Pountney et ah, 1994). Although the role of specific metallothionein isoforms in zinc homeostasis and apoptosis is established, its primary function in copper metabolism remains enigmatic (Vasak and Hasler, 2000). 

Both the overall rate of protein synthesis and the translation of certain specific mRNAs are controlled by agents such as hormones, growth factors, and other extracellular stimuli. As precursors for protein assembly, amino acids also regulate the translational machinery. Because protein synthesis consumes a high proportion of cellular metabolic energy, the energy status of the cell also modulates translation factors. 

Epinephrine, a hormone made in the adrenal medulla and sympathetic nerve endings, calls for rapid mobilization of energy and glucose. Epinephrine, like glucagon, binds to specific cellular receptors and activates adenylate cyclase. For the most part, epinephrine can be considered... 

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