Daily Olympiad: Chemistry - Biomolecules [20260512] – 4 Practice Problems & Printable PDF

1. Which of the following correctly describes the mechanism of an enzyme's active site according to the Induced Fit Model?

A. A) The substrate perfectly fits the active site without inducing any change. B. B) The enzyme and substrate induce reciprocal structural changes. C. C) The substrate binds to a different site to activate the enzyme. D. D) The active site remains rigid and unchanged upon substrate binding.

Solution

Correct: B

The Induced Fit Model posits that both the enzyme and substrate undergo conformational changes to achieve optimal binding. Unlike the rigid lock-and-key model, this mechanism emphasizes flexibility in the active site, allowing it to mold around the substrate. Choice B describes this reciprocal adjustment, while choices A and D incorrectly suggest rigidity. Choice C misrepresents the allosteric site interaction.

2. Which of the following is an allosteric regulator of the enzyme phosphofructokinase in glycolysis?

A. A) ATP B. B) Fructose 2,6-bisphosphate C. C) AMP D. D) NADH

Solution

Correct: A

Phosphofructokinase is a key regulatory enzyme. ATP and NADH act as negative allosteric inhibitors when energy is sufficient. AMP signals low energy and activates it. Fructose 2,6-bisphosphate acts as a positive modulator. The question focuses on ATP, which directly inhibits the enzyme in high-energy states, making A the correct answer.

3. Which monosaccharide is the reducing end in maltose but the non-reducing end in cellobiose?

A. A) Glucose in alpha(1->4) linkage B. B) Glucose in beta(1->4) linkage C. C) Fructose in beta(1->2) linkage D. D) Galactose in alpha(1->6) linkage

Solution

Correct: A

Maltose consists of two alpha-D-glucose linked by alpha(1->4), leaving one glucose free to act as a reducing agent. Cellobiose is beta-1,4 linked, and both hydroxyl groups remain occupied, making them non-reducing. The key distinction lies in the glycosidic linkage. Option A and B clarify alpha vs beta linkages, with A being correct for maltose.

4. Which of the following enzymes is NOT involved in DNA replication?

A. A) Helicase B. B) Topoisomerase C. C) DNA ligase D. D) RNA polymerase

Solution

Correct: D

DNA replication requires helicase to unwind DNA, topoisomerase to relieve tension, and ligase to join fragments. RNA polymerase synthesizes RNA primers but is not part of DNA replication itself. The correct answer is D, as DNA polymerase, not RNA polymerase, participates in replication.