The following images attempt to illustrate
the major events involved in the insulin signaling pathway responsible for increasing a cell's glucose uptake. Clicking on each of the
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see the Flash movie for the following sequence of images,
When blood glucose levels rise, insulin from the pancreas travels through the blood stream to a fat cell.
Insulin then binds to an Insulin Receptor (IR) found in the cell's plasma membrane. Phosphate groups are then added to the IR through the process of autophosphorylation.
Several additional proteins are in turn phosphorylated as the signal is transferred down the pathway.
One of the last proteins in the pathway then moves away from the plasma membrane towards the GLUT4 storage vesicle pool.
When the insulin signal pathway is inactive, GLUT4 storage vesicles (GSVs) are held in a recycling state, a short distance from the cell membrane.
When the signal that was originally sent by insulin reaches the GSV pool, the vesicles are released from their holding pattern and move toward the plasma membrane.
The GSV pool then merges with the plasma membrane allowing many additional GLUT4 proteins to transport glucose into the cell.
This leads to a a great increase in the amount of glucose taken in by the target cells.