Question

Given below are two statements:
Statement I: Enzyme can be regulated allosterically if it has at least one ligand-binding site other than the active site
Statement II: Enzyme can be regulated by phosphorylation and dephosphorylation.
In the light of the above statements, choose the most appropriate answer from the options given below

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true but Statement II is false
• D. Statement I is false but Statement II is true

Hint:

Metabolic Regulation:
Allosteric Regulation = Non-covalent binding at secondary site (e.g., PFK-1).
Covalent Modification = Phosphorylation Dephosphorylation (e.g., Glycogen phosphorylase).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Enzyme activity in metabolic pathways is fine-tuned through non-covalent allosteric modulation and reversible covalent modification.

Step 2: Detailed Explanation:
1. Statement I: Allosteric regulation occurs when an effector ligand (activator or inhibitor) binds reversibly to a dedicated regulatory/allosteric site distinct from the catalytic active site, inducing a conformational shift between the relaxed (R) and tense (T) quaternary states. Hence, Statement I is true.
2. Statement II: Reversible covalent modification (e.g., protein kinases adding phosphate to Ser/Thr/Tyr residues and protein phosphatases removing them, such as in glycogen phosphorylase) is a universal regulatory mechanism. Hence, Statement II is true.

Step 3: Final Answer:
Therefore, Both Statement I and Statement II are true, corresponding to option (A).