Answer: B. The linear sequence of amino acids in a polypeptide chain.
Explanation: Protein structure is the three dimensional arrangement of amino acid molecules in polypeptide chain.
Protein has four types of structure -
1-Primary structure
2-secondary structure
3- Tertiary structure
4- Quaternary structure
Primary structure of protein is the simplest form of protein where amino acids are arranged in linear way. One end of polypeptide chain is Called C-terminal (Carboxyl group )and other is called N terminal (amino group). Peptide bods play important role in establishing primary structure of protein.