BIOMATERIALS — Identify the principal structural component. Question: The major structural ingredient that gives leather its strength and flexibility is:

Introduction / Context:
Leather is produced by tanning animal hides. Its desirable properties—tensile strength, flexibility, and durability—come from the biological macromolecules present in skin. Understanding which macromolecule dominates helps in grasping tanning chemistry and material performance.

Given Data / Assumptions:

• Leather originates from animal skin (hide) after tanning.
• Skin extracellular matrix has a fibrous protein network.
• We distinguish proteins from carbohydrates, nucleic acids, and synthetic polymers.

Concept / Approach:
Collagen is a fibrous structural protein forming triple-helical fibrils that provide mechanical integrity to skin, tendons, and connective tissue. Tanning stabilizes collagen by crosslinking, making it less susceptible to putrefaction and water damage. Carbohydrates (e.g., glycans) and nucleic acids exist in tissues but are not the primary load-bearing framework; synthetic polymers are not inherent to genuine leather.

Step-by-Step Solution:
Identify the dominant biopolymer in animal hide → collagen.Relate tanning chemistry: crosslinking agents (vegetable tannins, chromium salts) stabilize collagen fibrils.Eliminate non-structural categories (carbohydrates, nucleic acids) and extraneous materials (synthetic polymers, chitin).

Verification / Alternative check:
Material science texts explicitly define leather as a collagen-based material whose performance depends on the degree of collagen stabilization and fiber orientation.

Why Other Options Are Wrong:
B) Carbohydrates are present but not the main structural protein matrix.C) “Polymer (synthetic)” refers to plastics, not natural leather.D) Nucleic acids are genetic materials, not structural.E) Chitin is a structural polysaccharide in arthropod exoskeletons, not in mammalian skin.

Common Pitfalls:
Assuming “polymer” means any chain molecule; here the correct class is a protein—collagen—rather than a synthetic polymer or carbohydrate.

Final Answer:
collagen