Final answer:
Insulin initiates a signaling cascade upon binding to its receptor that leads to glucose uptake into cells by promoting the translocation of glucose transporters, particularly Glut4, to the cell membrane.
Step-by-step explanation:
The presence of insulin is crucial for insulin-sensitive cells, such as skeletal muscle cells and adipose cells, to uptake glucose. Insulin facilitates this process not by acting as a transport protein itself, but by triggering a chain reaction inside the cell. Once insulin binds to its tyrosine kinase receptor, it starts a cascade of phosphorylation of proteins including IRS-1. This action leads to the translocation of glucose transporters, specifically the Glut4 transporter, to the cell membrane. These transporters then enable glucose to move from the bloodstream into the cell interior through facilitated diffusion.
Insulin's action is vital not only for glucose uptake but also for glucose metabolism, including glycogen synthesis and fatty acid synthesis. In absence of insulin or when there is insulin resistance, as seen in type 2 diabetes, glucose uptake by cells is hampered leading to elevated blood glucose levels.