Insulin signaling and transduction pathways play a major role in the regulation of metabolic homeostasis. All cells in the body are mainly fueled by glucose that is transported through blood vessels. The intricate process, which includes ensuring that glucose is made available when needed and stored when there is an excess, is controlled by a complex signaling system. The 2 key hormones at the center of these pathways are insulin and glucagon. It is important to understand insulin signaling because problems in the system impair the management of blood sugar levels, leading to diabetes mellitus.
Insulin and Glucagon
The beta cells in the pancreas release insulin when there is an abnormal rise in blood sugar levels. Insulin initiates the uptake of glucose for storage and metabolism. On the other hand, glucagon is released by the alpha cells in the pancreas when blood glucose levels are below the normal range. Glucagon then stimulates the liver cells to release glucose into the bloodstream. Both hormones are recognized by the cells’ receptors.
Insulin Receptors
Following a carbohydrate-rich diet, the concentration of glucose in the blood rises. High blood sugar can be toxic to the body. As a result, the cells in the body, such as the skeletal muscle cells, absorb excess glucose and store it as glycogen. Insulin is the vital messenger of the signal transduction pathway because it permits the cells to absorb glucose and convert it into glycogen. Insulin binds to the cells’ insulin receptors, which contain tyrosine protein kinase domains.
Signaling and Transduction Pathways
- Tyrosine protein kinase domains undergo auto-phosphorylation and activates the receptors.
- The receptor then binds and phosphorylates insulin receptor substrate (IRS) proteins, which bind to another molecule called phosphoinositide 3-kinase (PI3 kinase).
- PI3-kinase activates PIP2 and PIP3, which in turn activates PDK1 (PIP3 dependent protein kinase).
- PDK activates Akt or protein kinase B.
- Akt diffuses across the cytoplasm to activate the conversion of glucose into glycogen
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