What role do proteins play in living organisms?

Protein is a nutrient that your body needs to develop in order to maintain its life. After water, protein is the most abundant substance in your body. You may know that your muscles are made of protein, but this substance in its various forms serves other important roles as well. For example, proteins help cells develop and communicate, act as enzymes and hormones, transport nutrients throughout the bloodstream, and repair damaged tissue. In other words, you cannot live without protein.