Insulin, crucial for blood sugar regulation, is produced by the pancreas's beta cells. It facilitates glucose entry into cells and prompts the liver to store glucose as glycogen.
Insulin's chemical nature:
- A peptide hormone, a short amino acid chain.
- Composed of two polypeptide chains (A and B) connected by disulfide bonds.
- This structure defines it as a protein.
In summary, insulin is a protein hormone, distinct from carbohydrates, lipids, or vitamins, built from amino acid sequences.
\[
\boxed{\text{Insulin is chemically a protein}}
\]