How do cell-free extracts help biochemists study chemical reactions?

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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.

Biochemists use cell-free extracts to investigate the specific mechanisms of enzymatic steps within metabolic pathways, which cannot be fully elucidated through studies of whole organisms or tissues.1

These extracts are produced by the physical disruption of cells, followed by the removal of cell walls and other debris. By breaking down the cellular structure, biochemists can overcome permeability barriers that might otherwise prevent external materials from accessing specific cell components.1

Once the cells are disrupted, the resulting mixture can be further fractionated using a centrifuge to isolate specific organelles—such as mitochondria or ribosomes—or the soluble fraction of the cytoplasm. These isolated components can then be purified and tested to determine their capacity to catalyze particular metabolic reactions. Ultimately, this approach allows researchers to isolate the specific enzyme involved in a reaction, enabling them to measure reaction rates and identify the factors that control enzyme activity.1