Final answer:
Proteins are essential nutrients that contribute to all body tissues and have various important functions, such as regulating body functions and fighting off infection.
Step-by-step explanation:
Proteins are essential nutrients for the human body. They are one of the building blocks of body tissue and can also serve as a fuel source. Proteins contribute to all body tissues, from the skin to the brain cells, and act as hormones to regulate body functions. Additionally, proteins have important roles in transporting, signaling, receiving, catalyzing, defending, allowing for movement, and fighting off infection.