Insulin has:

Options

A. primary structure
B. secondary structure
C. tertiary structure
D. quaternary structure

Explanation

To answer the question "Insulin has:", we will break down the information provided in the video transcript step by step.

### Step-by-Step Solution:

1. **Identify the Type of Protein**:
- Insulin is classified as a **globular protein**. This means it has a compact, spherical shape, which is typical for proteins that are soluble in water.

**Hint**: Remember that globular proteins are often involved in metabolic processes and are soluble in aqueous environments.

2. **Understand the Composition**:
- Insulin is a **polypeptide**. This indicates that it is made up of a chain of amino acids linked by peptide bonds.

**Hint**: Polypeptides are formed when amino acids are joined together; the sequence and number of amino acids determine the protein's properties.

3. **Amino Acid Count**:
- The structure of insulin consists of **two chains of amino acids**: one chain has **21 amino acids**, and the other has **30 amino acids**. This specific arrangement is crucial for its biological function.

**Hint**: The number of amino acids in each chain is important for the protein's structure and function.

4. **Quaternary Structure**:
- Insulin exhibits a **quaternary structure**, which means it is composed of multiple polypeptide chains (subunits) that are arranged together. This is essential for its functional activity.

**Hint**: Quaternary structure is a higher-level organization of proteins, where multiple polypeptide chains interact to form a functional unit.

5. **Arrangement**:
- The polypeptide chains in insulin are arranged in a **closely packed manner**. This compact arrangement is vital for the stability and functionality of the protein.

**Hint**: The spatial arrangement of the chains can affect how the protein interacts with other molecules.

### Final Answer:
Insulin has a globular structure, is a polypeptide made up of two chains consisting of 21 and 30 amino acids, exhibits a quaternary structure, and is arranged in a closely packed manner.