Biochemistry

Step 1: Define the terms.

Peptide bond: The covalent bond linking amino acids together.
Collagen helix: The unique left-handed helical structure of an individual polypeptide chain of collagen.
Tropocollagen: The fundamental structural unit of a collagen fibril. It consists of three polypeptide chains (alpha chains), which are wound around each other to form a right-handed triple helix.
Tertiary structure: The overall 3D folding of a single polypeptide chain. \end{itemize}
Step 2: Match the definition to the question. The question asks for the name of the triple helical structure itself. This structure, formed by three intertwined polypeptide chains, is called tropocollagen. While "Collagen helix" refers to the structure of a single chain, "tropocollagen" refers to the complete three-chain unit.