Problem 23 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The correct match between Item I and Item II is: Item I (A) Allosteric effect (B) Competitive inhibitor (C) Receptor Item II (P) Molecule binding to the active site of enzyme (Q) Molecule crucial for communication in the body (R) Molecule binding to a site other than the active site of enzyme (S) Molecule binding to the enzyme covalently (a) (A) \(\square(\mathrm{R}) ;\) (B) \(\square(\mathrm{P}) ;\) (C) \(\square(\mathrm{Q}) ;\) (D) \(\square(\mathrm{S})\) (b) \((\mathrm{A}) \square(\mathrm{P}) ;(\mathrm{B}) \square(\mathrm{R}) ;(\mathrm{C}) \square(\mathrm{Q}) ;(\mathrm{D}) \square(\mathrm{S})\) (c) \((\mathrm{A}) \square(\mathrm{R}) ;(\mathrm{B}) \square(\mathrm{P}) ;(\mathrm{C}) \square(\mathrm{S}) ;(\mathrm{D}) \square(\mathrm{Q})\) (d) \((\mathrm{A}) \square(\mathrm{P}) ;\) (B) \(\square(\mathrm{R}) ;(\mathrm{C}) \square(\mathrm{S}) ;(\mathrm{D}) \square(\mathrm{Q})\)

Step-by-Step Solution

Answer

The correct answer is choice (a).

Step 1: Understand Item I Terms

Begin by understanding the terms in Item I: - **Allosteric effect (A)**: Occurs when a molecule binds to a site on an enzyme that is not the active site, causing a change in the enzyme's activity. This is generally a regulatory mechanism. - **Competitive inhibitor (B)**: A type of enzyme inhibitor that binds to the active site of the enzyme, preventing the actual substrate from binding. - **Receptor (C)**: A protein molecule that receives and responds to neurotransmitters or hormones, crucial for communication in the body.

Step 2: Understand Item II Terms

Next, interpret the options in Item II: - **(P) Molecule binding to the active site of enzyme**: This description matches with competitive inhibitors, as they compete with the substrate by binding to the active site. - **(Q) Molecule crucial for communication in the body**: This describes receptors, which often bind ligands such as hormones or neurotransmitters and play critical roles in cellular communication. - **(R) Molecule binding to a site other than the active site of enzyme**: This fits allosteric effects, as they occur when molecules bind non-active sites, influencing enzyme activity. - **(S) Molecule binding to the enzyme covalently**: This is generally related to irreversible inhibition, which doesn't directly match any term in Item I.

Step 3: Match Terms from Item I to Item II

Use the definitions and understanding of Items I and II to establish the correct connections: - **(A) Allosteric effect** matches with **(R)**: Molecule binding to a site other than the active site. - **(B) Competitive inhibitor** matches with **(P)**: Molecule binding to the active site of enzyme. - **(C) Receptor** matches with **(Q)**: Molecule crucial for communication in the body.

Step 4: Find the Correct Answer Choice

Based on the matches derived:- (A) corresponds to (R)- (B) corresponds to (P)- (C) corresponds to (Q)Review the answer choices provided:(a) (A) \( \square(\mathrm{R}) ; \) (B) \( \square(\mathrm{P}) ; \) (C) \( \square(\mathrm{Q}) ; \)Choice (a) correctly matches the derived connections: (A)-(R), (B)-(P), (C)-(Q).

Step 5: Confirm the Solution

The answer choice (a) matches the logical associations derived from scientific definitions. Ensure that all matches were correctly identified and cross-referenced with the answer choices given.

Key Concepts

Allosteric Regulation

Allosteric regulation is a fascinating phenomenon in enzyme activity and control. In simpler terms, an allosteric effect occurs when a molecule binds to an enzyme at a spot other than the usual active site, known as an allosteric site. This binding induces a conformational change in the enzyme.

Instead of directly competing with the substrate for the active site, the molecule modifies the enzyme's shape in such a way that it can either enhance or inhibit the enzyme's ability to bind to the substrate. This is why allosteric regulators are crucial in controlling metabolic pathways.

• Allosteric activators increase enzyme activity, allowing the substrate to better fit into the active site.
• Conversely, allosteric inhibitors decrease the activity, possibly preventing substrate binding altogether.

Allosteric regulation is a key mechanism for feedback control in biosynthetic pathways. It enables the fine-tuning of enzyme activity, which is essential for the dynamic balance of anabolic and catabolic reactions within cells.

Competitive Inhibition

Competitive inhibition is a type of enzyme inhibition where an inhibitor molecule competes with the substrate by binding to the enzyme's active site. Think of it like musical chairs, where both the inhibitor and the substrate vie for the same seat—the enzyme's active site. Because the inhibitor mimics the substrate's structure, it can bind to the active site and block the actual substrate from engaging.

This type of inhibition is often reversible. The effects can often be overcome by simply increasing the concentration of the substrate, effectively 'outnumbering' the inhibitor. There are some important aspects to note about competitive inhibition:

• It can be represented through the Michaelis-Menten equation, where the presence of a competitive inhibitor raises the apparent Michaelis constant (\(K_m\)), as more substrate is needed to reach the half-maximum velocity of the reaction.
• However, the maximum velocity (\(V_{max}\)) remains unchanged because, given sufficient substrate concentration, all enzymes will eventually bind substrate rather than inhibitor.

Competitive inhibition serves as a crucial mechanism for controlling enzyme activity in metabolic pathways, and many drugs and endogenous molecules exert their effects through this type of inhibition.

Molecular Receptors

Molecular receptors are specialized protein molecules that play a central role in cell signaling and communication. Imagine them as intricate lock-and-key systems, where these receptors are the locks situated on the cell surface or within the cell itself, waiting for their specific ligands—the keys.

When a ligand, such as a hormone, neurotransmitter, or drug, binds to the receptor, it triggers a series of cellular responses. Here are some features of molecular receptors:

• They can be located on the cell surface or within cell compartments, allowing them to interact with various signaling molecules.
• Depending on their type, they can influence numerous physiological processes, including metabolism, neuronal pathways, and cellular growth.

One classic example is G protein-coupled receptors (GPCRs), which are involved in detecting molecules outside the cell and activating internal signal transduction pathways. Understanding how molecular receptors function is vital for developing pharmaceuticals, as many drugs specifically target these receptors to modulate their activity in treating diseases.