Final answer:
DNA is the macromolecule that is stably maintained without being recycled. Carbon is critical as a fundamental element in all macromolecules due to its bonding capabilities. Myelin primarily consists of lipids and proteins.
Step-by-step explanation:
The macromolecule that is not recycled but is instead stably maintained within cells is DNA. DNA is essential for storing genetic information and is passed from generation to generation with high fidelity. Unlike other macromolecules like proteins, carbohydrates, and lipids, which are regularly broken down and synthesized based on the needs of the cell, DNA is maintained to ensure genetic information remains constant, barring rare mutations.
Carbon is a fundamental element in all macromolecules. It is crucial because of its ability to form four covalent bonds with different atoms, creating a versatile backbone for the structure of these molecules.
The biological macromolecules perform various functions essential to life and, combined, make up the majority of a cell's dry mass. Myelin, for example, is primarily composed of lipids and proteins, showcasing the diversity of structures and functions these macromolecules can exhibit.