Proteins are essential molecules that perform a wide range of functions in living organisms. They act as enzymes, which speed up chemical reactions, and as structural components, providing support and shape to cells and tissues. Proteins also play crucial roles in transporting molecules, signaling between cells, and defending against pathogens. Additionally, proteins are involved in muscle contraction and movement, allowing organisms to interact with their environment. Each protein's specific function is determined by its unique structure, which is shaped by the sequence of amino acids it contains. This relationship between structure and function is fundamental to the biology of all living things.