AP Syllabus focus:
‘The specific structure and function of enzymes help regulate biological processes by controlling when and how reactions occur.’
Enzymes regulate metabolism because their three-dimensional structures determine catalytic function and provide built-in “control points.” Cells tune enzyme activity rapidly and reversibly, coordinating pathways to match changing conditions and cellular demands.
Enzyme structure as the basis of regulation
Enzymes are proteins whose function depends on maintaining precise folding, which positions key amino acid side chains to stabilize reaction intermediates and bind regulatory molecules.
Primary structure (amino acid sequence) influences folding patterns.
Secondary and tertiary structure create specific pockets and surfaces that interact with other molecules.
Practice Questions
FAQ
In cooperative enzymes, conformational changes in one subunit alter the activity of other subunits.
This can create a steep response: small changes in regulator concentration produce large changes in enzyme activity.
Isoenzymes are different protein forms that catalyse the same reaction but differ in amino acid sequence and regulatory properties.
They allow tissue-specific control (e.g., different activity ranges or regulation by different signalling molecules).
Phosphate addition changes local charge and hydrogen bonding, but the effect depends on the protein’s fold.
If phosphorylation stabilises the active conformation it activates; if it stabilises an inactive conformation or blocks key movements it inhibits.
Activation often involves proteolytic cleavage, permanently removing a peptide segment that maintained inactivity.
Because the original structure cannot be restored by simple dissociation, turning activity off typically requires degradation or inhibition instead.
Cells can limit metal ions or coenzymes by transport, sequestration, or binding proteins.
If the cofactor is required to form the active catalytic structure, reducing its availability lowers the fraction of active enzyme molecules.
