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NEET 2023 Botany Question 110 Solution

Topic: Biotechnology: Principles and Processes · Official NTA Booklet Code G5

Question

During the purification process for recombinant DNA technology, addition of chilled ethanol precipitates out

(1)Polysaccharides
(2)RNA
(3)DNA
(4)Histones

✓

Verified Against NTA Final Answer Key

Option (3) : DNA

📚 Biotechnology: Principles and Processes Easy

📋 Given Parameters & Problem Setup

Process Purification of recombinant DNA

Reagent Added Chilled ethanol (ice-cold

C_2H_5OH

)

Observed Phenomenon Precipitation as fine white threads

⚡

The 30-Second Exam Hall Shortcut: ⚡ Spooling Anchor: Chilled Ethanol = DNA Precipitation

⏱️ Save ~20 seconds

After enzymatic digestion of RNA (RNase) and proteins (proteases), adding ice-cold (chilled) ethanol precipitates pure DNA as a collection of fine threads that can be spooled out!

1 Cell lysis releases macromolecules.

2 RNase digests RNA; proteases digest histones/proteins; polysaccharides/lipids removed.

3 Addition of chilled ethanol reduces dielectric constant of solution, causing negatively charged DNA to precipitate.

4 Precipitated DNA is gathered via spooling.

5 Match Option (3) DNA.

🛡️

Why You Can 100% Trust This Shortcut: Canonical NCERT Biotechnology laboratory isolation protocol.

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Enzymatic Removal of Cellular Contaminants

To obtain pure genetic material, bacterial/plant cells are digested with lysozyme/cellulase, followed by selective enzyme treatments:

\begin{aligned} \text{RNA removal} & \longrightarrow \text{Ribonuclease (RNase)} \\[3pt] \text{Protein removal} & \longrightarrow \text{Proteases (proteinase K)} \\[3pt] \text{Polysaccharides/lipids} & \longrightarrow \text{Differential extraction / detergent lysis} \end{aligned}

Step 2

Ethanol Precipitation Chemistry

Because DNA is a polyanionic macromolecule surrounded by a hydration shell of water molecules, adding cold ethanol lowers the dielectric constant, allowing monovalent cations ( $Na^+$ ) to neutralize the phosphate backbone, precipitating DNA out of solution:

\text{Purified aqueous DNA} \xrightarrow{\text{Chilled Ethanol } (C_2H_5OH)} \text{\textbf{Precipitated DNA threads (Spooling)}}

Step 3

Collection by Spooling

The precipitated DNA is visible as a tangle of fine white threads and is collected onto a glass rod by spooling.

⭐

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:

Polysaccharides are degraded by enzymes (cellulase/pectinase) or removed in organic phases during initial lysis.

⚠️

Student Fallacy (Why candidates pick this trap): Assuming all polymers precipitate simultaneously.

2 2

✗ Incorrect

Verdict & Scientific Reason:

RNA is digested by ribonuclease (RNase) prior to ethanol addition so it does not precipitate as the intact target nucleic acid.

⚠️

Student Fallacy (Why candidates pick this trap): Forgetting that RNase treatment precedes ethanol precipitation.

3 3

✓ 100% Correct

Verdict & Scientific Reason:

Matches NCERT verbatim: addition of chilled ethanol ultimately precipitates out purified DNA.

💡

Why this is airtight: None; textbook verbatim.

4 4

✗ Incorrect

Verdict & Scientific Reason:

Histones are basic proteins digested by proteases into soluble peptides, not precipitated intact.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing chromatin proteins with the nucleic acid backbone.

⚠️

NTA Trap Alert: Order of Reagents Trap

Students confuse the role of enzymes (RNase, proteases) with the role of chilled ethanol. Enzymes degrade contaminants, whereas chilled ethanol precipitates the DNA.

🛡️ How to avoid the -1 mark: Enzymes digest RNA and protein; Chilled ethanol precipitates DNA!

📖

Core NEET Syllabus Standard

NCERT Biology · Biotechnology: Principles and Processes Standard Benchmark

Core Scientific Principle Tested:

"Other molecules can be removed by appropriate treatments and purified DNA ultimately precipitates out after the addition of chilled ethanol. This can be seen as collection of fine threads in the suspension."

Syllabus Focus: Isolation of the Genetic Material (DNA)

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2023 Botany Question 110 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Spooling Anchor: Chilled Ethanol = DNA Precipitation

Step-by-Step Rigorous Workflow & Mathematical Proof

Enzymatic Removal of Cellular Contaminants

Ethanol Precipitation Chemistry

Collection by Spooling

360° Option Elimination Engine Key Feature

NTA Trap Alert: Order of Reagents Trap

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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