Final answer:
Nitrogen (N) is the element found in all proteins and not in carbohydrates or lipids, and it is essential for the structure and function of proteins.
Step-by-step explanation:
The element found in all proteins and not in carbohydrates or lipids is nitrogen (N). Proteins consist of amino acids, with each containing an amino group that includes nitrogen. This distinguishes proteins from other macronutrients; while carbohydrates and lipids are primarily composed of carbon, hydrogen, and oxygen, proteins also contain nitrogen, making it integral to their structure and function.
Furthermore, sulfur (S) is found in certain amino acids, adding to the complexity of protein structure. Proteins perform various critical roles in the human body, including the formation of enzymes, antibodies, and hormones, all of which are dependent on their unique amino acid compositions.