What is insulin?

• A. a mineral
• B. a type of protein called a hormone
• C. a carbohydrate
• D. an enzyme

Answer: (B)

Insulin is a protein hormone produced by the pancreas that helps regulate blood sugar. Hormones are chemical messengers that travel through the bloodstream to distant cells, and insulin signals liver, muscle, and fat cells to take in glucose from the blood. This action promotes glucose uptake and storage as glycogen in the liver and muscles, and it also lowers glucose production by the liver. Because it is made of amino acids and functions to signaling cells, insulin is a protein hormone—not a mineral, not a carbohydrate, and not an enzyme (which would catalyze a chemical reaction). Insulin’s proper signaling is essential for maintaining steady blood glucose levels; dysfunction here is a key feature of diabetes.