Which function is associated with cholesterol?

Cholesterol plays several critical roles in the body, and one of its primary functions is being an integral part of cell membranes. It helps to maintain the structural integrity and fluidity of these membranes, allowing for proper cellular function and communication. In addition to its role in cell membranes, cholesterol is also a precursor for the synthesis of steroid hormones, such as cortisol, estrogen, and testosterone. These hormones are essential for various physiological processes, including metabolism, immune response, and reproductive functions.

The other functions mentioned in the choices are not directly related to cholesterol. For instance, amino acid formation is primarily the result of protein metabolism, while insulin production occurs in the pancreas and is not dependent on cholesterol. Similarly, although appetite enhancement can be influenced by various hormones and nutritional factors, it is not a direct function of cholesterol. Therefore, the integral role of cholesterol in cell membranes and steroid hormone production distinctly defines its functions within the body.