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Glucose transporters are a wide group of membrane proteins that facilitate the transport of glucose across the plasma membrane, a process known as facilitated diffusion. Because glucose is a vital source of energy for all life, these transporters are present in all phyla .
When insulin binds to the receptors on the cell surface, vesicles containing the GLUT4 transporters come to the plasma membrane and fuse together by the process of endocytosis, thus enabling a facilitated diffusion of glucose into the cell. As soon as the glucose enters the cell, it is phosphorylated into glucose-6-phosphate in order to ...
Upon reaching the plasmalemma, the vesicles fuse with the membrane, increasing the number of GLUT4 transporters expressed at the cell surface, and hence increasing glucose uptake. GLUT4 has a Km value for glucose of about 5 mM, which as stated above is the normal blood glucose level in healthy individuals.
Glucose enters the beta cells and goes through glycolysis to form ATP that eventually causes depolarization of the beta cell membrane (as explained in Insulin secretion section of this article). The depolarization process causes voltage-controlled calcium channels (Ca2+) opening, allowing the calcium to flow into the cells.
It is an integral membrane protein carrier with a hydrophilic interior, which allows it to bind to glucose. As GLUT 1 is a type of carrier protein, it will undergo a conformational change to allow glucose to enter the other side of the plasma membrane. [22] GLUT 1 is commonly found in the red blood cell membranes of mammals. [23]
Once glucose enters the cell, the first step is phosphorylation of glucose by a family of enzymes called hexokinases to form glucose 6-phosphate (G6P). This reaction consumes ATP, but it acts to keep the glucose concentration inside the cell low, promoting continuous transport of blood glucose into the cell through the plasma membrane transporters.
Substances that enter the cell via signal mediated electrolysis include proteins, hormones and growth and stabilization factors. [36] Viruses enter cells through a form of endocytosis that involves their outer membrane fusing with the membrane of the cell. This forces the viral DNA into the host cell. [37]
Insulin and glucagon are the primary hormones involved in maintaining a steady level of glucose in the blood, and the release of each is controlled by the amount of nutrients currently available. [17] The amount of insulin released in the blood and sensitivity of the cells to the insulin both determine the amount of glucose that cells break ...