The rhythm of hormones in genes

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Hormones are the major signaling molecules that have a complex signaling cascade involving intracellular and intranuclear receptors, coreceptors, and signal transduction pathways. The molecular mechanism of hormonal action is written in a poetic verse to kindle the interest of students and to augment their affinity toward the onerous yet awesome topic. The hormones are secreted from the site of their synthesis and carried by transport binding proteins to exert their action in their target cells at a different site. Cortisol and aldosterone are derived from cholesterol with pregnenolone as an intermediate. Cortisol binds to the Glucocorticoid receptor (GR) in the cytoplasm by displacing the heat shock protein (hsp) already bound to it. The receptor ligand complex then traverses the nuclear membrane and binds to the Glucocorticoid Responsive Element (GRE) in the DNA. Except the orphan receptors, the nuclear receptors of thyroid, retinol (Vitamin A) and calcitriol (Vitamin D) exist as heterodimers and are bound to the DNA by their DNA binding domains. These nuclear receptors exist as heterodimers partnered with RXR (retinoic x receptor). Binding of insulin to its receptor on the target cells results in a cascade of intracellular events that involves activation of various kinases like PDK, mTOR and MAPK. This leads to phosphorylation of signal molecules that mediates the actions of insulin. Somatotropin (Growth hormone) and prolactin acts by JAK-STAT pathway where the phosphorylated STAT protein dimerises and translocates to the nucleus and binds to Interferon Responsive Element and activates transcription. Somatotropin prevents dwarfism by promoting growth and prolactin promotes synthesis of milk by mammary glands. The communication between the nuclear receptors (FXR, LXR, PPAR-Gamma) and the basal transcription apparatus is accomplished by protein - protein interaction between the nuclear receptors and the nuclear coregulators like CREB, TRAP and DRIP. These coregulators bind to various coactivators and transcription factors that activate RNA polymerase resulting in the synthesis of Pre-pri RNA strand. Hence hormones act as first messengers that initiates the expression of genetic message in the codon of genes as protein synthesis by a process of translation.