| 1.2 Elements of Life |
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Summary
All biological macromolecules are assembled from atoms obtained from the environment. A small set of elements — carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur (CHNOPS) — makes up the great majority of every living organism.
Carbon, hydrogen, and oxygen
- Form the universal backbone of carbohydrates, proteins, lipids, and nucleic acids
Additional elements
- Sulfur is found in some proteins (in the amino acids cysteine and methionine)
- Phosphorus is found in phospholipids, nucleic acids, and ATP
- Nitrogen is found in nucleic acids and proteins (in amino acids)
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.