Each polypeptide in a protein has amino acids linked with each other in a specific sequence. This sequence of amino acids is said to be... .

Options

A. primary structure of proteins
B. secondary structure of proteins
C. tertiary structure of proteins
D. quateranary structure of proteins

Explanation

To answer the question, "Each polypeptide in a protein has amino acids linked with each other in a specific sequence. This sequence of amino acids is said to be...", we need to understand the different levels of protein structure.

### Step-by-Step Solution:

1. **Understanding Polypeptides**: A polypeptide is a chain of amino acids linked together by peptide bonds. Proteins can consist of one or more polypeptide chains.

2. **Sequence of Amino Acids**: The specific order in which amino acids are arranged in a polypeptide is crucial because it determines the protein's structure and function.

3. **Levels of Protein Structure**:
- **Primary Structure**: This refers to the linear sequence of amino acids in a polypeptide chain. It is the simplest level of protein structure and is determined by the genetic code.
- **Secondary Structure**: This involves the local folding of the polypeptide chain into structures such as alpha helices and beta sheets, which are stabilized by hydrogen bonds.
- **Tertiary Structure**: This is the overall three-dimensional shape of a single polypeptide chain, formed by further folding and interactions between secondary structures.
- **Quaternary Structure**: This refers to the arrangement of multiple polypeptide chains (subunits) in a multi-subunit protein.

4. **Identifying the Correct Answer**: The question specifically asks about the sequence of amino acids in a polypeptide. This sequence is defined as the **primary structure** of the protein.

5. **Conclusion**: Therefore, the answer to the question is that the sequence of amino acids linked together in a polypeptide is referred to as the **primary structure of proteins**.

### Final Answer:
The sequence of amino acids in a polypeptide is said to be the **primary structure of proteins**.

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