Specific region of a protein where secondary structure changes to another and a single function can occur...

### Domain

## Step1: Understanding the Question### The question is asking about a specific region in a protein where secondary structure changes to another and a single function can occur. This is a fundamental concept in molecular biology and protein structure.## Step2: Identifying the Key Concepts### The key concepts in this question are "secondary structure", "function", and "region of a protein". Secondary structure refers to the local folding of the protein backbone, which includes alpha helices and beta sheets. A function refers to the role that the protein plays in the body. A region of a protein is a part of the protein that has a specific role.## Step3: Applying the Concepts### In molecular biology, a domain is a distinct functional unit of a protein. It is a region of a protein that can fold independently and perform a specific function. This fits the description given in the question.