What structural level of protein involves the coiling of a single polypeptide chain stabilised by H-bonds ?

Explanation

To answer the question regarding the structural level of protein that involves the coiling of a single polypeptide chain stabilized by hydrogen bonds, we can break down the solution into the following steps:

### Step-by-Step Solution:

1. **Understanding Proteins**:
- Proteins are large biomolecules made up of one or more long chains of amino acids. The sequence of amino acids in these chains determines the protein's structure and function.

2. **Levels of Protein Structure**:
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