Second Messenger In Signal Transduction
Signal transduction and second messengers
Fig. 37.22. Different steps involved in 'signal transaction pathways' for regulation of cistron expression due to action of (a) protein/peptide hormones; (b) steroid and thyroid hormones (likewise note cross-linking between two pathways).
In animals as well equally in plants, the cellular machinery for protein synthesis responds to external stimuli. These external stimuli may include a whole range of diverse factors including the post-obit : (i) the presence of hormones, growth factors and other signalling molecules (e.m. in animals); (ii) the presence of pheromones secreted past cells of two dissimilar mating types (i.e. in yeast); (three) presence of calorie-free (different wave lengths), gravity, minerals, water, gases and specific soil structure (due east.yard. in plants) and (iv) cell-cell contact. In some of these cases, cell surface receptor molecules are nowadays and transmit the signal to the interior of the prison cell (for water-soluble signals like proteins, peptides and neurotransmitters). In other cases, substances like hormones interact with intracellular receptors, which transmit the signal further to the target site (for h2o insoluble lipophilic signals like steroids, thyroid hormones, retinoic acid, etc.). In all these cases (including prokaryotes), the external stimulus needs to exist transduced and integrated with internal signals, which follow a cascade of events called- 'betoken transduction pathway' -leading to the response, which is a specific gene expression in many cases (Fig. 37.22).
Fig. 37.22. Different steps involved in 'signal transaction pathways' for regulation of gene expression due to action of (a) poly peptide/peptide hormones; (b) steroid and thyroid hormones (likewise annotation cross-linking between ii pathways).
Signal transduction pathways precede about of the mechanisms for regulation of gene expression discussed earlier. In prokaryotes, frequently the precursor molecule (e.g. lactose) or the end product (e.chiliad. an amino acid) of a biosynthetic pathway takes part in regulation of gene activeness. Only in 'signal transduction pathways' in eukaryotes a cascade of molecules, leading to the activation of one or more specific transcription factors, is involved in regulation of gene action.
The extracellular 'signals' in the form of ligands, are transduced beyond the plasma membrane to cell compartments (nucleus and other cells organelles) via a variety of molecules described every bit 'second messengers'. The 'effectors' i.due east. molecules which bind to specific receptors to initiate the pathways for the production of 'second messengers', are often described as 'first messengers'. The binding of this effector to receptor is often- mediated past a protein, whose activity depends on GTP/GDP bounden. These GTP/Gross domestic product binding proteins are called G-proteins (run across Genetics of Cancer : Proto-oncogenes, Oncogenes and Tumour Suppressor Genes). There is also another set of cytosolic effectors, through which 'second messengers' produce a wide variety of cellular responses. Although there are millions of molecules which send signals into the cell interior, only one-half a dozen or then '2d messengers' have and then far been identified (e.g. cAMP, cGMP, DAG, IP3, Caii+, etc.). Actually, signal transduction pathways are besides known, which do non involve whatsoever 'second messenger' molecules (east.chiliad. response to interferon a, insulin, steroid and thyroid hormones, etc.).
Second Messenger In Signal Transduction,
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