Which element distinguishes proteins from carbohydrates and lipids?

Which element distinguishes proteins from carbohydrates and lipids?

• A. Carbon
• B. Hydrogen
• C. Oxygen
• D. Nitrogen

Answer: (D)

Proteins are defined by containing nitrogen in their amino groups of amino acids. Every amino acid has an -NH2 group, and these nitrogens are carried through into the protein's structure as amino acids link together with peptide bonds. Carbohydrates and lipids, in contrast, are built from carbon, hydrogen, and oxygen and do not have nitrogen in their basic backbones, so nitrogen presence is what sets proteins apart. While some special lipid molecules can include nitrogen in rare cases, the typical and defining difference is that proteins contain nitrogen, whereas the common forms of carbohydrates and lipids do not.

Proteins are defined by containing nitrogen in their amino groups of amino acids. Every amino acid has an -NH2 group, and these nitrogens are carried through into the protein's structure as amino acids link together with peptide bonds. Carbohydrates and lipids, in contrast, are built from carbon, hydrogen, and oxygen and do not have nitrogen in their basic backbones, so nitrogen presence is what sets proteins apart. While some special lipid molecules can include nitrogen in rare cases, the typical and defining difference is that proteins contain nitrogen, whereas the common forms of carbohydrates and lipids do not.