A `beta`-pleated sheet organization in a polypeptide chain is an example of -

Options

A. 1° structure
B. 2° structure
C. `3^(@)` structure
D. `4^(@)` structure

Answer

To determine the type of structure represented by a beta-pleated sheet in a polypeptide chain, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Protein Structure Levels**:
- Proteins have four levels of structure: primary, secondary, tertiary, and quaternary. Each level describes a different aspect of the protein's formation and organization.

2. **Identify the Primary Structure**:
- The primary structure of a protein refers to the linear sequence of amino acids connected by peptide bonds. This sequence determines the protein's overall structure and function.

3. **Define Secondary Structure**:
- The secondary structure involves the local folding of the polypeptide chain into shapes such as alpha helices or beta-pleated sheets. These structures are stabilized by hydrogen bonds between the backbone atoms in the polypeptide chain.

4. **Recognize Beta-Pleated Sheets**:
- Beta-pleated sheets are a specific type of secondary structure. They consist of beta strands connected laterally by at least two or three backbone hydrogen bonds, forming a sheet-like structure.

5. **Conclusion**:
- Since a beta-pleated sheet is a form of local folding in the polypeptide chain, it is classified as a secondary structure of proteins.

### Final Answer:
A beta-pleated sheet organization in a polypeptide chain is an example of **secondary structure**.

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