What is insulin considered to be?

• A. A lipid
• B. Protein, hormone, and a signaling molecule
• C. A carbohydrate
• D. A nucleic acid

Answer: (B)

Insulin is a protein hormone that acts as a signaling molecule. It’s produced by pancreatic beta cells as a peptide hormone and travels through the bloodstream to bind to insulin receptors on target cells. This binding triggers a signaling cascade that promotes glucose uptake into muscle and fat tissues and reduces glucose production by the liver, helping to lower blood glucose after meals. It’s not a lipid, carbohydrate, or nucleic acid because those categories refer to fats, sugars, and nucleic acids, respectively, which have different building blocks and roles. Structurally, insulin is a small polypeptide with amino acids arranged in two chains linked by disulfide bonds, typical of proteins.