Control of (blank) synthesis is the key to controlling the chemical pathway of the cell.

Controlling the synthesis of proteins is the key to controlling the chemical pathways in the cell.

This is because proteins have key roles in many chemical reactions in the cell.

The most important proteins for the chemical reactions in the cell are enzymes.

Enzymes catalyze many chemical reactions, therefore, the control of the enzyme synthesis is a direct way of controlling other chemical reactions in the cell.