PSI Barbering Practice Exam

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Which element is a key component of all proteins?

  1. Sulfur

  2. Carbon

  3. Iron

  4. Nitrogen

The correct answer is: Nitrogen

A key component of all proteins is nitrogen. Proteins are made up of amino acids, and every amino acid contains an amino group (-NH2) that includes nitrogen. This nitrogen is essential for forming the peptide bonds that link amino acids together to create protein chains. In addition to nitrogen, amino acids also contain carbon, hydrogen, and oxygen, but nitrogen is the distinctive element that sets proteins apart from carbohydrates and fats, which do not contain nitrogen in their structures. While sulfur is found in some amino acids and iron is an important mineral for various biological functions, neither is necessary for the formation of all proteins. Therefore, the presence of nitrogen is what fundamentally characterizes proteins.

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