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Why do proteins make up a large portion of a cell's macromolecules?

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Diagram showing how epinephrine binding to a beta-adrenergic receptor on a cell membrane activates a G-protein, which then stimulates adenylyl cyclase to convert ATP into cyclic AMP (cAMP), leading to physiological effects such as increased heart rate, blood vessel dilation, and glycogen breakdown. — Biochemistry In biochemistry, researchers study the chemical substances and processes that occur in living organisms and cells. In particular, various processes by which cells gain energy, such as epinephrine-stimulated cAMP synthesis, have been deduced through the study of biochemistry.

Proteins constitute the largest portion of a cell's macromolecules—accounting for approximately 18 percent of a typical mammalian cell's total weight—because they are essential for the vast array of activities required for life.1

Their prevalence is driven by their functional versatility:

Catalysis: The majority of enzymes in a cell are proteins. These molecules catalyze nearly all metabolic reactions, enabling the cell to build, convert, and degrade necessary chemical substances.231
Structural Support: Proteins provide critical structural elements that maintain the integrity of the cell and bind cells together into tissues.23
Regulation and Defense: Proteins control gene activity, act as hormones for regulation, and function as antibodies to protect against disease.23
Evolutionary Advantage: Proteins are composed of about 20 different amino acids, which provide a greater diversity of side chains than the nucleotides found in RNA. This allows proteins to fold into complex, unique three-dimensional shapes that form efficient functional surfaces, making them more capable of complex tasks than other macromolecules.1