Proteins differ from carbohydrates and lipids in that, they always contain nitrogen, carbon, hydrogen and oxygen.

Explanation

**Step-by-Step Solution:**

1. **Understanding Proteins**: Proteins are complex biomolecules made up of long chains of amino acids. Each amino acid contains specific elements that contribute to the overall structure of proteins.

2. **Composition of Amino Acids**: Each amino acid, the building block of proteins, contains:
- A central carbon atom
- An amino group (-NH2) which contains nitrogen
- A carboxyl group (-COOH) which contains oxygen
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