Biology · Biomolecules · NEET
NCERT gives 4 steps in this exact order. Step 1: the substrate S binds to the active site, fitting into it. Step 2: this binding makes the enzyme change its shape so it fits more tightly around the substrate. Step 3: the active site now breaks the chemical bonds of the substrate and the enzyme-product (EP) complex is formed. Step 4: the enzyme releases the products and the free enzyme is ready to bind a new substrate. So the flow is E + S to ES to EP to E + P.
ES = enzyme-substrate complex. It forms first, when S binds the active site. It is short-lived (transient). EP = enzyme-product complex. It forms later, after the enzyme has broken the substrate's bonds, but before the product leaves. So ES comes before bond breaking and EP comes after bond breaking. The full path is E + S to ES to EP to E + P.
Yes. This is step 2 in NCERT. When the substrate binds the active site, the enzyme is induced to alter its shape and fit more tightly around the substrate. This is why the active site is not a rigid lock. In NEET the wrong option often skips this shape-change step, so remember it comes right after binding.
The EP complex forms in step 3, at the moment the active site breaks the chemical bonds of the substrate. The substrate has now become the product but is still held by the enzyme. Right after this, in step 4, the enzyme releases the product. So EP is a very brief stage between bond breaking and product release.
While the substrate is bound to the active site (during the ES stage), a new unstable structure called the transition state is formed. It is the highest-energy point between the stable substrate and the stable product. The enzyme lowers the energy needed to reach this transition state, which is how it speeds up the reaction. It sits between ES and EP in the pathway.
Regarding catalytic cycle of an enzyme action, select the correct sequential steps: A. Substrate enzyme complex formation. B. Free enzyme ready to bind with another substrate. C. Release of products. D. Chemical bonds of the substrate broken. E. Substrate binding to active site.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
E + S to ES to EP to E + P. The enzyme (E) joins the substrate (S) to make the ES complex, this becomes the EP complex after bonds break, then the enzyme and product (P) separate.
No. NCERT calls the ES complex a transient (short-lived) phenomenon. It forms and then quickly moves on to the EP stage and product release.
NCERT states the formation of the ES complex is essential for catalysis. Without the substrate binding the active site first, the reaction cannot be speeded up. Questions test whether you know binding must come before bond breaking.
No. In step 4 the free enzyme is released unchanged and is ready to bind another substrate molecule and run the cycle again. This is why enzymes act again and again.
The catalytic cycle is the fixed order of steps inside one reaction. Factors affecting enzyme activity (temperature, pH, substrate concentration) change how fast that cycle runs, not the order of the steps.
