Proteins are complex macromolecules vital for nearly every biological process in living organisms. Structurally, they are polymers formed by linking smaller components called amino acids into chains via peptide bonds. These chains can fold into specific, functional three-dimensional structures, determining their biochemical roles. Functionally, proteins serve numerous purposes, acting as structural elements in tissues, components of enzymes that catalyze chemical reactions, and regulators in metabolic pathways. They are critical for maintaining immune defense, transporting molecules throughout the circulatory system, and facilitating energy management, making them fundamental nutrients for growth and repair.