Question: 128: Primary proteins are also called as polypeptides because :
(1) They are linear chains
(2) They are polymers of peptide monomers
(3) Successive amino acids are joined by peptide bonds
(4) They can assume many conformations
Answer: Option (3)
Explanation:
The primary structure of a protein refers to the specific sequence of amino acids present in the polypeptide chain.
In proteins, amino acids are linked to each other through peptide bonds.
A peptide bond is formed between the carboxyl group of one amino acid and the amino group of the next amino acid with the release of a water molecule.
Thus, the protein consists of a long chain of amino acids connected by successive peptide bonds.
Because of this continuous chain of amino acids joined by peptide bonds, primary proteins are also called polypeptides.
Being linear or having multiple conformations does not define the term polypeptide.
Hence, the correct answer is that successive amino acids are joined by peptide bonds.