Insulin is important in stimulating the uptake of glucose from blood in the skeletal muscle and adipose tissue. It is secrered by pancreatic β cells throμgh a glucose sensing pathway. Insulin also increases cell permeability to monosaccharides, amino acids and fatty acids. Insulin is first formed as a precursor molecule, preproinsulin which is then processed into proinsulin and finally to the mature insulin hormone. A mature form of insulin has an A chain and a B chain that are connnected by two dilsufide bonds. Defects in insulin are the cause of type-II diabetes mellitus.