Insulin and Glucose Regulation of Glycogenesis

This educational video by Andrey K explains the molecular mechanisms by which insulin and glucose regulate glycogenesis in liver cells. It begins by describing the physiological context: after exercise, a carbohydrate-rich meal raises blood glucose levels, prompting the pancreas to secrete insulin. Insulin binds to its receptor on liver cells, initiating a signal transduction pathway that activates protein kinases. These kinases phosphorylate and inactivate glycogen synthase kinase (GSK), which normally keeps glycogen synthase in its inactive form. However, inactivation of GSK alone is insufficient; glycogen synthase must be dephosphorylated to its active form by protein phosphatase 1 (PP1). The video then details how glucose itself acts as a signal: it binds to phosphorylase A in its R state, causing a conformational change to the T state, which reduces its affinity for PP1 and leads to dissociation. This releases active PP1, which dephosphorylates glycogen synthase B to glycogen synthase A, promoting glycogenesis. Additionally, PP1 dephosphorylates phosphorylase A to phosphorylase B, preventing reassociation and ensuring sustained glycogen synthesis. The video concludes with a summary of the entire pathway, emphasizing the coordinated roles of insulin and glucose in replenishing glycogen stores.