Which of the following elements is present in proteins but not typically found in carbohydrates or lipids?

In proteins, nitrogen is a fundamental component that distinguishes them from carbohydrates and lipids. While all three macromolecules—proteins, carbohydrates, and lipids—contain carbon, hydrogen, and oxygen, proteins uniquely incorporate nitrogen as part of their amino acid structures. Amino acids are the building blocks of proteins, and each contains an amine group (-NH2), which contains nitrogen. This element plays a critical role in the formation of peptide bonds between amino acids, enabling the diverse structures and functions of proteins in biological systems.

Carbohydrates and lipids, on the other hand, do not contain nitrogen in their composition. Carbohydrates are primarily made of carbon, hydrogen, and oxygen, typically in a structure of (CH2O)n, while lipids mostly consist of long hydrocarbon chains with some oxygen, but lacking nitrogen. Thus, the presence of nitrogen is a characteristic feature that specifically identifies proteins among the biomolecules.