Elements of life

Summary

All biological macromolecules are assembled from atoms obtained from the environment.

Carbon, hydrogen, and oxygen

• form the universal backbone of carbohydrates, proteins, lipids, and nucleic acids

Additional elements

• sulfur for proteins

• phosphorus for phospholipids and nucleic acids

• nitrogen for nucleic acids and proteins

Understanding which elements belong to which macromolecule is essential for predicting how nutrient limitations affect cellular function.

Because organisms cannot manufacture elements, they depend on environmental sources for every atom they incorporate into biological molecules. A deficiency in even one element — such as nitrogen or phosphorus — can disrupt the synthesis of all macromolecules that require it, with cascading effects on cell structure, energy storage, genetic information, and membrane integrity. Tracing individual elements to specific macromolecule classes is a foundational skill tested repeatedly on the AP exam.