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

Options

A. a) `1^(@)` structure
B. b) `2^(@)` structure
C. c) `3^(@)` structure
D. d) `4^(@)` structure.

Answer

To answer the question about the `beta`-pleated sheet organization in a polypeptide chain, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Protein Structure**:
- Proteins are made up of polypeptide chains formed by amino acids linked together by peptide bonds. The arrangement and interaction of these amino acids lead to different structural levels.

2. **Levels of Protein Structure**:
- There are four levels of protein structure: primary, secondary, tertiary, and quaternary.
- **Primary Structure**: This is the linear sequence of amino acids in a polypeptide chain.
- **Secondary Structure**: This involves the folding or coiling of the primary structure into specific shapes, primarily due to hydrogen bonding.

3. **Identifying Secondary Structures**:
- The secondary structure can be further divided into two main types:
- **Alpha Helix**: A coiled structure stabilized by hydrogen bonds.
- **Beta-Pleated Sheet**: A folded structure where segments of the polypeptide chain lie parallel or antiparallel to each other, forming a sheet-like appearance.

4. **Conclusion**:
- The `beta`-pleated sheet is a specific type of secondary structure in proteins. Therefore, the correct answer to the question is that a `beta`-pleated sheet organization in a polypeptide chain is an example of **secondary structure**.

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

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