Q.139 Botany ⭐ 360° Option Elimination Active

Vault ↗

NEET 2023 Botany Question 139 Solution

Topic: Biomolecules · Official NTA Booklet Code G5

Question

Melonate inhibits the growth of pathogenic bacteria by inhibiting the activity of

(1)Dinitrogenase
(2)Succinic dehydrogenase
(3)Amylase
(4)Lipase

✓

Verified Against NTA Final Answer Key

Option (2) : Succinic dehydrogenase

📚 Biomolecules Easy

📋 Given Parameters & Problem Setup

Inhibitor Malonate (Melonate, structural analogue of succinate)

Biological Role Inhibits bacterial growth via competitive enzyme inhibition

⚡

The 30-Second Exam Hall Shortcut: ⚡ Textbook Competitive Inhibition Classic: Malonate = Succinic Dehydrogenase

⏱️ Save ~20 seconds

The classic NCERT textbook example of competitive enzyme inhibition: Malonate closely resembles the substrate Succinate in structure, competitively inhibiting Succinic Dehydrogenase in the TCA cycle!

1 Substrate: Succinate (

\text{HOOC-CH}_2\text{-CH}_2\text{-COOH}

2 Competitive inhibitor: Malonate (

\text{HOOC-CH}_2\text{-COOH}

3 Target enzyme: Succinic dehydrogenase.

4 By blocking succinic dehydrogenase, microbial cellular respiration is halted, inhibiting bacterial growth.

5 Match Option (2) Succinic dehydrogenase.

🛡️

Why You Can 100% Trust This Shortcut: Canonical NCERT Biomolecules enzyme kinetics and inhibition prototypes.

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Mechanism of Competitive Enzyme Inhibition

When an inhibitor closely resembles the natural substrate in its molecular structure and competes for the active catalytic site of the enzyme, it is a competitive inhibitor:

\begin{aligned} \text{Substrate:} & \quad \text{Succinate } (^{-}OOC-CH_2-CH_2-COO^-) \\[3pt] \text{Competitive Inhibitor:} & \quad \text{Malonate } (^{-}OOC-CH_2-COO^-) \\[3pt] \text{Target Enzyme:} & \quad \mathbf{\text{Succinic Dehydrogenase}} \end{aligned}

Step 2

Verbatim NCERT Reference

NCERT states under Enzymes: "Inhibition of succinic dehydrogenase by malonate which closely resembles the substrate succinate in structure. Such competitive inhibitors are often used in the control of bacterial pathogens."

Step 3

Reversibility of Competitive Inhibition

Because the inhibitor binds reversibly to the catalytic active site without altering the enzyme permanently, competitive inhibition can be overcome by increasing substrate concentration ( $K_m$ increases, $V_{\max}$ remains unchanged).

⭐

360° Option Elimination Engine Key Feature

Diagnose every choice: Know exactly why the right option works and why distractors fail.

4-Option Deep Scan

1 1

✗ Incorrect

Verdict & Scientific Reason:

Dinitrogenase (nitrogenase) fixes nitrogen into ammonia in diazotrophs; it is poisoned by molecular oxygen, not malonate.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing nitrogen fixation enzymes with Krebs cycle dehydrogenases.

2 2

✓ 100% Correct

Verdict & Scientific Reason:

Exact NCERT prototype of competitive inhibition: malonate inhibits succinic dehydrogenase.

💡

Why this is airtight: None; textbook prototype.

3 3

✗ Incorrect

Verdict & Scientific Reason:

Amylase hydrolyzes alpha-1,4-glycosidic bonds in starch into maltose; it is unrelated to malonate.

⚠️

Student Fallacy (Why candidates pick this trap): Guessing a general digestive enzyme.

4 4

✗ Incorrect

Verdict & Scientific Reason:

Lipase hydrolyzes triglycerides into glycerol and fatty acids, having no interaction with malonate.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing lipid metabolism with respiration.

⚠️

NTA Trap Alert: Spelling Variation Trap ("Melonate" vs. "Malonate")

The NEET question printed "Melonate" instead of "Malonate". Students often hesitate or overthink whether "melonate" is a completely different compound.

🛡️ How to avoid the -1 mark: Recognize standard NEET exam typographical variants: Melonate is the printed variant for Malonate.

📖

Core NEET Syllabus Standard

NCERT Biology · Biomolecules Standard Benchmark

Core Scientific Principle Tested:

"Inhibition of succinic dehydrogenase by malonate which closely resembles the substrate succinate in structure is used in the control of bacterial pathogens."

Syllabus Focus: Enzymes (Factors Affecting Enzyme Activity)

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Ready to attempt under real exam pressure?

Test your speed and accuracy in the authentic 200-minute timed NTA simulator.

Launch NEET 2023 CBT Test →

← Previous (Q.138) All Botany Questions Grid Next (Q.140) →

Classification & Functions of Biomolecules (Proteins, Polysaccharides & Secondary Metabolites)

View Solution →

Spotted a mistake in this solution? Report an error (support@mycompetitiveexams.com)

⚖️ Legal & Fair Dealing Notice: Sourced from publicly released NEET 2023 question papers and NEET answer keys for private study, research, and non-commercial educational practice under Fair Dealing (Section 52(1)(a) of the Indian Copyright Act, 1957). Not affiliated with or endorsed by NTA or NMC.

NEET 2023 Botany Question 139 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Textbook Competitive Inhibition Classic: Malonate = Succinic Dehydrogenase

Step-by-Step Rigorous Workflow & Mathematical Proof

Mechanism of Competitive Enzyme Inhibition

Verbatim NCERT Reference

Reversibility of Competitive Inhibition

360° Option Elimination Engine Key Feature

NTA Trap Alert: Spelling Variation Trap ("Melonate" vs. "Malonate")

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — Biomolecules

Secondary and Tertiary Structural Conformations of Proteins

Lassaigne's Sodium Fusion Test for Sulfur & Amino Acid Diagnostic

Classification of Vitamins and Their Primary Dietary Sources

Classification & Functions of Biomolecules (Proteins, Polysaccharides & Secondary Metabolites)

Solve 4 NEET Questions a Day — One per Subject