`beta` - pleated structure of proteins is

Options

A. Primary structure
B. Secondary structure
C. Tertiary structure
D. Quaternary structure

Answer

To determine the correct answer to the question about the beta-pleated structure of proteins, let's break down the information step by step.

### Step-by-Step Solution:

1. **Understanding Proteins**:
- Proteins are polymers made up of amino acids. They play crucial roles as building blocks in the body.

2. **Levels of Protein Structure**:
- Proteins have four levels of structure: primary, secondary, tertiary, and quaternary.

3. **Primary Structure**:
- The primary structure refers to the linear sequence of amino acids in a polypeptide chain. This is the first level of protein structure.

4. **Secondary Structure**:
- The secondary structure is formed when the linear sequence of amino acids folds into specific shapes. The two common types of secondary structures are:
- **Alpha Helix**: A coiled structure.
- **Beta-Pleated Sheet**: A sheet-like structure formed by hydrogen bonds between different segments of the polypeptide chain.

5. **Tertiary Structure**:
- The tertiary structure is the three-dimensional arrangement of the secondary structures. It represents the overall shape of a single polypeptide chain.

6. **Quaternary Structure**:
- The quaternary structure involves the arrangement of two or more polypeptide chains into a larger complex. Not all proteins have a quaternary structure.

7. **Identifying the Correct Answer**:
- Since the question specifically asks about the beta-pleated structure, we identify that this structure is classified under the secondary structure of proteins.

### Conclusion:
The beta-pleated structure of proteins is classified as the **secondary structure**.