Hormones like insulin, glucagon, and growth hormone are all proteins. Remember: if it's made of amino acids and performs biological signaling, it's most likely a protein.
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.
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\boxed{\text{Insulin is chemically a protein}}
\]