Insulin is

Options

A. Polysaccharide
B. Protein
C. Oligosaccharide
D. Lipid

Answer

**Step-by-Step Solution:**

1. **Identify the Nature of Insulin**: Insulin is a hormone that plays a crucial role in regulating blood sugar levels in the body.

2. **Source of Insulin**: It is secreted by the pancreas, specifically from a region known as the islets of Langerhans.

3. **Cell Types in Islets of Langerhans**: The islets contain three types of cells: alpha cells, beta cells, and delta cells. Among these, only the beta cells are responsible for producing insulin.

4. **Structure of Insulin**: The structure of insulin consists of peptide chains, specifically an A chain and a B chain.

5. **Proinsulin and C Chain**: In its precursor form, known as proinsulin, there is an additional C chain present. However, this C chain is not found in mature insulin.

6. **Chemical Bonds**: The A and B chains of insulin are connected by disulfide bridges, which are a type of covalent bond. These chains are also stabilized by hydrogen bonds.

7. **Conclusion**: Since insulin is composed of peptide chains made up of amino acids, it is classified as a protein.

8. **Final Answer**: Therefore, the correct answer to the question "Insulin is" is **protein**.

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