Here's why:

* Enzymes: Catalyze (speed up) biochemical reactions.

* Structural components: Provide support and shape to cells and tissues (e.g., collagen, keratin).

* Hormones: Act as chemical messengers (e.g., insulin, growth hormone).

* Antibodies: Defend against pathogens.

* Transport proteins: Carry molecules across membranes (e.g., hemoglobin).

* Storage proteins: Store nutrients (e.g., casein in milk).

* Contractile proteins: Enable movement (e.g., actin, myosin).

* Receptors: Bind to signaling molecules and initiate cellular responses.

While other biological molecules like carbohydrates, lipids, and nucleic acids have important roles, proteins exhibit the broadest range of functions within living organisms.