Short answers, pulled from the story.
Frederick Banting and Charles Best first isolated insulin from a dog's pancreas in 1921, working in John Macleod's laboratory at the University of Toronto. On the 30th of July 1921 their extract, which they called isletin, reduced a diabetic dog's blood sugar by 40 percent in one hour.
Insulin is the body's main anabolic hormone, and it lowers blood sugar by driving glucose from the blood into liver, fat, and skeletal muscle cells. There the glucose is stored as glycogen through glycogenesis or as triglycerides through lipogenesis, while the liver's own glucose production is strongly inhibited.
In type 1 diabetes an autoimmune reaction destroys the insulin-producing beta cells, causing absolute insulin deficiency. In type 2 diabetes the beta cell loss is milder and not autoimmune, involving amyloid accumulation in the pancreatic islets and peripheral tissue insulin resistance, alongside glucagon secretion that no longer responds to blood glucose.
Human insulin is composed of 51 amino acids and has a molecular mass of 5808 daltons. It is a heterodimer of a 21-amino-acid A-chain and a 30-amino-acid B-chain linked by disulfide bonds, with a molecular formula of C257H383N65O77S6.
Frederick Banting and John Macleod received the 1923 Nobel Prize in Physiology or Medicine for the discovery of insulin. Banting shared his half with Charles Best and Macleod shared his with James Collip; later, Frederick Sanger won the 1958 Chemistry prize for sequencing insulin and Rosalyn Sussman Yalow won in 1977 for the insulin radioimmunoassay.
The discoverers assigned the insulin patent to the University of Toronto's Board of Governors on the 15th of January 1923 for a token payment of one dollar. They did this so that no commercial firm could secure a profitable monopoly, allowing anyone to prepare the extract once the method was published.