Insulin is a hormone produced by the beta cells of the pancreas. It plays a crucial role in regulating glucose levels in the human body at a molecular level. When blood glucose levels rise, such as after a meal, insulin is released into the bloodstream. Insulin helps maintain glucose homeostasis by facilitating glucose uptake into cells and regulating glucose metabolism. Here's how insulin works at a molecular level:1. Insulin binds to insulin receptors: Insulin molecules circulate in the bloodstream and bind to specific insulin receptors on the surface of target cells, such as muscle, liver, and adipose fat cells. Insulin receptors are transmembrane proteins that span the cell membrane, with an extracellular domain that binds insulin and an intracellular domain that initiates a signaling cascade.2. Activation of insulin receptor substrate IRS : When insulin binds to its receptor, it activates the receptor's intrinsic kinase activity. This leads to autophosphorylation of the receptor and subsequent phosphorylation of insulin receptor substrate IRS proteins. Phosphorylated IRS proteins serve as docking sites for other signaling molecules.3. Activation of PI3K/Akt pathway: One of the key signaling molecules that bind to phosphorylated IRS proteins is phosphoinositide 3-kinase PI3K . PI3K generates phosphatidylinositol 3,4,5 -trisphosphate PIP3 , which in turn recruits and activates protein kinase B Akt . Akt is a serine/threonine kinase that phosphorylates and regulates the activity of various target proteins involved in glucose metabolism.4. Glucose transporter GLUT translocation: Akt activation leads to the translocation of glucose transporter proteins GLUT from intracellular vesicles to the cell surface. In muscle and adipose cells, the primary glucose transporter is GLUT4. The presence of GLUT4 on the cell surface allows glucose to enter the cell via facilitated diffusion.5. Glycogen synthesis and glycolysis: Once inside the cell, glucose can be used for energy production through glycolysis or stored as glycogen. Insulin promotes glycogen synthesis by activating glycogen synthase, the enzyme responsible for converting glucose into glycogen. Insulin also stimulates glycolysis by increasing the activity of key glycolytic enzymes, such as hexokinase and phosphofructokinase.6. Inhibition of gluconeogenesis: In the liver, insulin inhibits gluconeogenesis, the process of generating glucose from non-carbohydrate sources. Insulin suppresses the expression of key gluconeogenic enzymes, such as phosphoenolpyruvate carboxykinase PEPCK and glucose-6-phosphatase, thereby reducing hepatic glucose output.By promoting glucose uptake into cells, stimulating glycogen synthesis and glycolysis, and inhibiting gluconeogenesis, insulin helps lower blood glucose levels and maintain glucose homeostasis in the human body.