Which of the following is NOT a function of proteins in the body?

Proteins play several crucial roles in the body, with each function illustrating their versatility and importance in biological processes. While options such as structural support, catalysis of reactions, and transport of oxygen highlight key functions of proteins, the aspect of energy production is generally not considered a primary function of proteins.

Proteins primarily serve as building blocks for tissues and organs, contributing to structural support in muscles, skin, and bones. Enzymes, which are proteins, facilitate biochemical reactions, acting as catalysts to speed up the body's metabolic processes. Additionally, certain proteins, like hemoglobin, are essential for the transport of oxygen in the bloodstream, ensuring that vital oxygen reaches tissues throughout the body.

In contrast, while proteins can be used as an energy source through deamination when carbohydrates and fats are not available, this is not their main role in metabolism. The body typically relies more on carbohydrates and fats for energy production. Therefore, the function of energy production is not a primary or defining role of proteins, making it the correct answer in this context.