Chemistry · Biomolecules · NEET
Enzymes are proteins, not polysaccharides. NCERT says almost all enzymes are globular proteins, built from amino acids linked by peptide bonds (-CONH-). This is a very common NEET trap: option "enzymes are polysaccharides" is always FALSE. Polysaccharides are carbohydrates like starch and cellulose, which are not enzymes.
No. A catalyst, including an enzyme, lowers the activation energy of BOTH the forward and backward reactions by the same amount. So the reaction reaches equilibrium faster, but the value of the equilibrium constant K at a given temperature stays the same. NEET tests this almost every year, so remember: catalyst changes SPEED, not the equilibrium constant and not the final amounts.
A cofactor is a non-protein helper that an enzyme needs to work. If this helper is a small organic molecule (often from a vitamin), it is called a coenzyme. If it is a metal ion (like Mg2+, Zn2+, Fe), it is called a metal cofactor. Coenzymes and cofactors increase the catalytic activity of the enzyme. This is why option "coenzymes increase the catalytic activity of enzyme" is TRUE.
The substrate binds to the active site of the enzyme, forming an enzyme-substrate complex. This gives an easier reaction path with a lower energy barrier (lower activation energy), so more molecules can cross it and the reaction goes faster. NCERT example: activation energy for acid hydrolysis of sucrose is 6.22 kJ/mol, but with the enzyme sucrase it drops to only 2.15 kJ/mol.
No. A catalyst does NOT initiate a reaction. It only speeds up a reaction that is already feasible (thermodynamically possible). If a reaction is non-spontaneous, no enzyme or catalyst can make it happen. NEET often hides this in a "which statement is not correct" question.
Mg2+ (magnesium). Enzymes called kinases transfer a phosphate group from ATP and need Mg2+ as the cofactor. The Mg2+ ion binds the phosphate groups of ATP, neutralises their negative charge, and stabilises the transition state. Among alkaline earth metals (Be, Mg, Ca, Sr), the answer is Mg.
The incorrect statement regarding enzymes is:
Which one of the following statements is not correct?
Enzymes that utilize ATP in phosphate transfer require an alkaline earth metal (M) as the cofactor. M is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
They are catalysts made by living cells that speed up biochemical reactions inside the body under mild conditions (normal body temperature and pH). Like all catalysts they are needed only in small amounts and are not used up in the reaction.
No. Like any catalyst, an enzyme is regenerated at the end and can be used again. Only a small quantity is needed to carry out a reaction many times.
Most enzymes are named after the substrate or class of compound they act on, with the ending -ase. Example: maltase hydrolyses maltose to glucose; oxidoreductase enzymes catalyse oxidation-reduction reactions.
Enzymes are far more specific (one enzyme usually acts on one substrate), work under mild body conditions, and are proteins. But like chemical catalysts, they lower activation energy and do not change the equilibrium constant.
For hydrolysis of sucrose, the activation energy with dilute acid is 6.22 kJ/mol, but with the enzyme sucrase it is only 2.15 kJ/mol. The enzyme makes the barrier much lower, so the reaction is much faster.
