What role do proteins play in biological systems?

Proteins are fundamental macromolecules with various critical roles in biological systems, and one of their primary functions is to act as enzymes and structural components. Enzymes, which are a specific type of protein, catalyze biochemical reactions, speeding them up and allowing cellular processes to occur efficiently. Without enzymes, many physiological functions would be too slow to sustain life.

Additionally, proteins serve as structural components in cells and tissues. For example, collagen provides strength and support to connective tissues, while keratin is a key structural element in hair and nails. These roles highlight the importance of proteins not only in facilitating biochemical reactions but also in maintaining the integrity and functionality of cells and tissues throughout the organism.

The other choices reflect different biological roles; for instance, while proteins can contribute to energy provision in certain cases (like through amino acids during prolonged fasting), they are not the primary energy source for cells—that role is mainly filled by carbohydrates and fats. Genetic information is stored in nucleic acids (DNA and RNA), and hemoglobin is the protein in red blood cells that actually transports oxygen, but it does not encompass the full spectrum of proteins' roles beyond transport.