Quaternary structure of protein is associated with :

Options

A. orientation of multi subunits of a protein
B. three-dimensional structure of a peptide chain
C. hydrogen bonding
D. amino acid sequence

Explanation

To answer the question about the quaternary structure of proteins, we will break down the concept step by step.

### Step-by-Step Solution:

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

2. **Defining Quaternary Structure**:
- The quaternary structure of a protein refers to the arrangement and interaction of multiple polypeptide chains (subunits) that come together to form a functional protein complex. This structure is crucial for the protein's function.

3. **Identifying Characteristics of Quaternary Structure**:
- The quaternary structure is characterized by:
- The number of subunits.
- The arrangement of these subunits in space.
- The interactions between the subunits, which can include hydrogen bonds, ionic bonds, and hydrophobic interactions.

4. **Evaluating the Options**:
- **Option 1: Orientation of multi subunits of protein** - This is correct as it directly relates to the quaternary structure.
- **Option 2: Three-dimensional structure of peptide chain** - This describes the tertiary structure, not quaternary.
- **Option 3: Hydrogen bonding** - While hydrogen bonds are important, they are primarily associated with tertiary structure.
- **Option 4: Amino acid sequence** - This pertains to the primary structure of proteins.

5. **Conclusion**:
- Based on the definitions and evaluations, the correct answer is **Option 1: Orientation of multi subunits of protein**.