Which type of biological molecule is insulin?

• A. Carbohydrate
• B. Protein (hormone)
• C. Lipid
• D. Nucleic acid

Answer: (B)

Insulin is classified as a protein, specifically a peptide hormone composed of amino acids. As a hormone, its primary role is to regulate glucose levels in the bloodstream by facilitating the uptake of glucose into cells, thus playing a critical role in metabolism and energy homeostasis.

Proteins are formed by long chains of amino acids that are folded into specific three-dimensional structures, allowing them to perform a wide range of functions within the body, including enzymatic activity and cell signaling. The structure and function of insulin exemplify the characteristics of proteins, as its activity is dependent on its specific structure, which is guided by the sequence of amino acids.

In contrast, carbohydrates serve primarily as energy sources and structural components in cells; lipids are involved in storing energy and forming cell membranes; and nucleic acids are responsible for storing and transmitting genetic information. These definitions help clarify why insulin is categorized as a protein hormone rather than any other type of biological molecule.