Signal transduction processes

Cells make use of many different types of membranes. All cells have a cytoplasmic membrane, or plasma membrane, that functions (in part) to separate the cytoplasm from the surroundings. In the early days of biochemistry, the plasma membrane was not accorded many functions other than this one of partition. We now know that the plasma membrane is also responsible for (1) the exclusion of certain toxic ions and molecules from the cell, (2) the accumulation of cell nutrients, and (3) energy transduction. It functions in (4) cell locomotion, (5) reproduction, (6) signal transduction processes, and (7) interactions with molecules or other cells in the vicinity. 

Natural or synthethic receptor ligands that induce a conformational change (active conformation) and a signal transduction process upon receptor binding. Agonists may act as typical hormones or neurotransmitters or they may confer paracrine functions, recognize bacterial, viral or other environmental constituents via activating their dedicated receptors. 

Ligand-induced signal transduction processes that are mediated by a ligand-operated ion channel, e.g., by the nicotinic receptor in muscle, result in an almost... 

Developmental exposure to Pb or Mm affect signal transduction process, possibly related to the modulation of nitric oxide as well as alterations in receptor-mediated phosphoinositide hydrolysis and protein kinase C (rats)... 

Figure 8.2 Simplified overview of the signal transduction process mediated by the JAK-STAT pathway. Refer to text for specific details...

Combinatorial chemistry has provided new ways for the pharmaceutical industry and for academic researchers to address specific problems in a time- and resource-efficient manner. Given the involvement of specific oligosaccharide structures in signal transduction processes, combinatorial carbohydrate libraries are... 

Refer to Section 2.7 and Fig. 2.5. It should be noted that the signal transduction process is very dynamic and there are many cascading pathways. This explains the need to have drugs with specific interactions to reduce other reactions that can give rise to adverse events (side effects). Section 2.9 shows the effects of drug specificity. 

The response may be local or via a signal transduction process. The rate for the forward reaction of drug binding to receptor is proportional to the concentrations of both the drug and target. Conversely, the rate for the reverse reaction (i.e., dissociation of the drug-receptor complex) is proportional to the concentration of the drug-receptor complex. At equilibrium, both forward and reverse reactions are equal. Mathematically, we have... 

Sis Growth factor Binds to receptor to initiate a signal transduction process. 

Like all signaling substances, neurotransmitters (see p. 352) act via receptor proteins. The receptors for neurotransmitters are integrated into the membrane of the postsynaptic cell, where they trigger ion inflow or signal transduction processes (see p. 348). 

A feature common to all oncogenes is the fact that they code for proteins involved in signal transduction processes. The genes are designated using three-letter abbreviations that... 

B. An antagonist binds to a receptor and prevents the action of an agonist. Choice A is wrong because this combination does initiate a signal transduction process. C and D are incorrect because both neurotransmitters and hormones work through their appropriate receptor to initiate signal transduction. 

As discussed for N-myristoylation and S-prenylation, even S-acylation of proteins with a fatty acid which in the vast majority of cases is the C16 0 palmitic acid, plays a fundamental role in the cellular signal-transduction process (Table l). 2-5 14 While N-myristoylation and S-prenylation are permanent protein modifications due to the amide- and sulfide-type linkage, the thioester bond between palmitic acid and the peptide chain is rather labile and palmi-toylation is referred to as a dynamic modification. 64 This reversibility plays a crucial role in the modulation of protein functions since the presence or absence of a palmitoyl chain can determine the membrane localization of the protein and can also be used to regulate the interactions of these proteins with other proteins. Furthermore, a unique consensus sequence for protein palmitoylation has not been found, in contrast to the strict consensus sequences required for N-myristoylation and S-prenylation. Palmitoylation can occur at N- or C-terminal parts of the polypeptide chain depending on the protein family and often coexists with other types of lipidation (see Section 6.4.1.4). Given the diversity of protein sequences... 

The regulation of the subtypes I, III and VIII by Ca /cahnodulin stands out. All three subtypes are stimulated by Ca, although in different concentration regions. Ca is, as discussed in more detail in Chapter 6, a central intracellular messenger substance, and an increase in the Ca concentration is observed on activation of different signal transduction processes. 

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