Britannica Sources used in this answer

How do cells control which enzymes they produce?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A multi-panel diagram illustrates how a substrate binds to an enzyme's active site through induced fit, leading to product formation, and shows how non-substrates and allosteric regulators can alter enzyme activity by binding to different sites on the enzyme. — Enzyme In the induced-fit theory of enzyme-substrate binding, a substrate approaches the surface of an enzyme (step 1 in box A, B, C) and causes a change in the enzyme shape that results in the correct alignment of the catalytic groups (triangles A and B; circles C and D represent substrate-binding groups on the enzyme that are essential for catalytic activity). The catalytic groups react with the substrate to form products (step 2). The products then separate from the enzyme, freeing it to repeat the sequence (step 3). Boxes D and E represent examples of molecules that are too large or too small for proper catalytic alignment. Boxes F and G demonstrate binding of an inhibitor molecule (I and I′) to an allosteric site, thereby preventing interaction of the enzyme with the substrate. Box H illustrates binding of an allosteric activator (X), a nonsubstrate molecule capable of reacting with the enzyme.

Cells control which enzymes they produce primarily by regulating gene expression, ensuring that proteins are synthesized only when and where they are required to conserve energy. This regulation occurs through several sophisticated mechanisms:1

Genetic and Transcriptional Control

Operons: In bacteria, genes coding for related enzymes are often clustered into operons. These systems use repressor proteins to block transcription when an enzyme is not needed, or inducers to activate production when a specific substrate is present.12
Transcription Factors: These proteins bind to specific DNA regions to determine whether a gene is transcribed into RNA. They act as master switches that control the efficiency and timing of enzyme synthesis.3
Epigenetic Regulation: Chemical modifications to DNA or histones, such as methylation or acetylation, can permanently or transiently silence or activate genes, allowing different cell types to express unique sets of enzymes despite sharing the same genetic code.45

Metabolic and Allosteric Control

While genetic control dictates whether an enzyme is made, cells also regulate the activity of existing enzymes through allosteric control. Feedback inhibition allows a metabolic pathway to shut down when its end product accumulates to sufficient levels, preventing the wasteful overproduction of substances.67