Q.150 Botany ⭐ 360° Option Elimination Active

NEET 2021 Botany Question 150 Solution

Topic: Biotechnology: Principles and Processes · Official NTA Booklet Code M1

Question

Plasmid pBR322 has PstI restriction enzyme site within gene ampR that confers ampicillin resistance. If this enzyme is used for inserting a gene for β-galactoside production and the recombinant plasmid is inserted in an E.coli strain

(1)it will not be able to confer ampicillin resistance to the host cell.
(2)the transformed cells will have the ability to resist ampicillin as well as produce β-galactoside.
(3)it will lead to lysis of host cell.
(4)it will be able to produce a novel protein with dual ability. Section - A (Biology: Zoology)

✓

Verified Against NTA Final Answer Key

Option (1) : it will not be able to confer ampicillin resistance to the host cell.

📚 Biotechnology: Principles and Processes Easy

📋 Given Parameters & Problem Setup

Cloning Vector Plasmid pBR322

Cloning Site PstI restriction site within ampR gene

Inserted Gene Gene for β-galactoside production

Host Organism E. coli

⚡

The 30-Second Exam Hall Shortcut: ⚡ Insertion within ampR = Insertional Inactivation of Ampicillin Resistance!

⏱️ Save ~20 seconds

The PstI restriction site is located right inside the ampicillin resistance gene ( $amp^R$ ) of pBR322! Inserting a foreign gene at this site disrupts the reading frame of $amp^R$ (insertional inactivation), rendering the recombinant plasmid INCAPABLE of conferring ampicillin resistance to host E. coli cells! Match Option (1)!

1 Plasmid pBR322 contains two antibiotic resistance genes:

amp^R

and

tet^R

2 PstI and PvuI restriction sites lie within the

amp^R

gene.

3 BamHI and SalI sites lie within the

tet^R

gene.

4 Insertion of foreign DNA at PstI disrupts the

amp^R

gene

\implies

Insertional inactivation.

5 Result: Transformed recombinant cells lose ampicillin resistance and become ampicillin-sensitive.

6 Match Option (1).

🛡️

Why You Can 100% Trust This Shortcut: Canonical NCERT Biotechnology Principles on Cloning Vectors and Insertional Inactivation.

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Restriction Architecture of Plasmid pBR322

Plasmid $pBR322$ has distinct unique restriction endonuclease recognition sites within selectable marker genes:

\begin{aligned} \mathbf{amp^R \text{ gene:}} & \quad \text{Contains recognition sites for } \mathbf{PstI} \text{ and } PvuI \\[4pt] \mathbf{tet^R \text{ gene:}} & \quad \text{Contains recognition sites for } BamHI \text{ and } SalI \end{aligned}

Step 2

Mechanism of Insertional Inactivation

When the foreign gene encoding $\beta$ -galactoside is ligated at the $PstI$ site, foreign DNA is inserted directly into the coding sequence of the $amp^R$ gene. This interruption destroys the integrity of the open reading frame, inactivating the production of functional $\beta$ -lactamase enzyme:

Step 3

Consequence to Host Cell

The host *E. coli* cells transformed with the recombinant plasmid will produce $\beta$ -galactoside, but will not be able to confer ampicillin resistance; they become sensitive to ampicillin and will fail to grow on medium containing ampicillin.

⭐

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1 1

✓ 100% Correct

Verdict & Scientific Reason:

This statement is completely TRUE. Insertion at the PstI site inside ampR destroys ampicillin resistance due to insertional inactivation.

💡

Why this is airtight: None. Flawless application of insertional inactivation.

2 2

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. The ampR gene has been disrupted and can no longer confer ampicillin resistance.

⚠️

Student Fallacy (Why candidates pick this trap): Assuming the host retains resistance while acquiring the new trait.

3 3

✗ Incorrect

Verdict & Scientific Reason:

The plasmid does not trigger a lytic cycle; lysis is characteristic of virulent bacteriophages, not non-lytic plasmids.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing plasmid vectors with lytic bacteriophages.

4 4

✗ Incorrect

Verdict & Scientific Reason:

Insertional inactivation destroys the native protein product of the disrupted marker gene rather than forming a functional chimeric fusion protein.

⚠️

Student Fallacy (Why candidates pick this trap): Speculating that insertional disruption fuses the two protein functions.

⚠️

NTA Trap Alert: PstI / PvuI vs BamHI / SalI Restriction Sites on pBR322

Remember which enzyme cuts which marker: PstI & PvuI cut $amp^R$ ; BamHI & SalI cut $tet^R$ .

🛡️ How to avoid the -1 mark: Mnemonic: "P = Penicillin/Ampicillin"

\implies

PstI cuts

amp^R

📖

Core NEET Syllabus Standard

NEET / NCERT Biology · Biotechnology: Principles and Processes Standard Benchmark

Core Scientific Principle Tested:

"Ligation of alien DNA at a restriction site present in one of the antibiotic resistance genes inactivates that gene (insertional inactivation). Recombinant plasmids will lose resistance to that antibiotic."

Syllabus Focus: Cloning Vectors: Selectable Markers and Insertional Inactivation

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2021 Botany Question 150 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Insertion within ampR = Insertional Inactivation of Ampicillin Resistance!

Step-by-Step Rigorous Workflow & Mathematical Proof

Restriction Architecture of Plasmid pBR322

Mechanism of Insertional Inactivation

Consequence to Host Cell

360° Option Elimination Engine Key Feature

NTA Trap Alert: PstI / PvuI vs BamHI / SalI Restriction Sites on pBR322

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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