Which of the following statements best describes proteins?

Proteins are often referred to as the building blocks of life due to their essential roles in the structure and function of cells. They are made up of amino acids, which link together in specific sequences to form various proteins that perform a multitude of functions in living organisms. These functions include serving as enzymes to catalyze biochemical reactions, forming structural components in tissues such as muscles and skin, and participating in processes like immune responses. The versatility and complexity of proteins enable them to contribute significantly to the growth, development, and maintenance of all living things.

While proteins can indeed provide hormonal signals and assist in energy metabolism, their primary and most defining role is as structural and functional components of cells, hence why the statement about them being the building blocks of living things is the most accurate descriptor.