`beta`- pleated structure of proteins is

Options

A. primary structure
B. secondary structure
C. Tertiary structure
D. Quatemary structure

Answer

To determine the classification of the beta-pleated structure of proteins, we will analyze the different levels of protein structure: primary, secondary, tertiary, and quaternary.

### Step-by-Step Solution:

1. **Understanding Primary Structure**:
- The primary structure of a protein refers to the linear sequence of amino acids linked by peptide bonds. This sequence is determined by the genetic code and is unique to each protein.
- **Conclusion**: The beta-pleated structure is not the primary structure.

2. **Understanding Secondary Structure**:
- The secondary structure of proteins refers to local folded structures that form within a polypeptide due to hydrogen bonding between the backbone atoms. The two most common types of secondary structures are alpha helices and beta-pleated sheets.
- The beta-pleated sheet is characterized by its zigzag formation, where strands of the polypeptide chain lie parallel or antiparallel to each other, stabilized by hydrogen bonds.
- **Conclusion**: The beta-pleated structure is indeed a secondary structure.

3. **Understanding Tertiary Structure**:
- The tertiary structure refers to the overall three-dimensional shape of a single polypeptide chain, which is formed by the interactions between the side chains (R groups) of the amino acids. This structure can include multiple types of secondary structures.
- **Conclusion**: The beta-pleated structure is not the tertiary structure, as it is a component of the secondary structure.

4. **Understanding Quaternary Structure**:
- The quaternary structure involves the assembly of multiple polypeptide chains into a single functional protein complex. This structure is stabilized by various interactions, including hydrogen bonds, ionic bonds, and hydrophobic interactions.
- **Conclusion**: The beta-pleated structure is not a quaternary structure, as it pertains to a single polypeptide chain.

### Final Answer:
The beta-pleated structure of proteins is classified as a **secondary structure**.