Q.7 Botany ⭐ 360° Option Elimination Active

Vault ↗

NEET 2020 Botany Question 7 Solution

Topic: Biotechnology: Principles and Processes · Official NTA Booklet Code E1

Question

Choose the correct pair from the following:

(1)Ligases - Join the two DNA molecules
(2)Polymerases - Break the DNA into fragments
(3)Nucleases - Separate the two strands of DNA
(4)Exonucleases - Make cuts at specific positions within DNA

✓

Verified Against NTA Final Answer Key

Option (1) : Ligases - Join the two DNA molecules

📚 Biotechnology: Principles and Processes Easy

📋 Given Parameters & Problem Setup

Enzyme Classes Ligases, Polymerases, Nucleases, Exonucleases

Question Objective Identify the correctly paired enzyme and function

⚡

The 30-Second Exam Hall Shortcut: ⚡ "Ligases = Ligate / Join; Nucleases = Cut / Hydrolyze"

⏱️ Save ~20 seconds

DNA Ligases catalyze phosphodiester bond formation to seal and join two DNA molecules (molecular glue!). Polymerases synthesize DNA (do not break it); Exonucleases cut from ends (not within). Pair (1) is the only correct pair! Select Option (1) in 5 seconds.

1 Check Pair (1): Ligases - Join two DNA molecules. Matches canonical function of DNA ligase (molecular glue) -> CORRECT!

2 Check Pair (2): Polymerases - Polymerize dNTPs to synthesize DNA, they do NOT break DNA into fragments -> False.

3 Check Pair (3): Nucleases - Cleave phosphodiester backbones, they do NOT separate strands (Helicase separates strands) -> False.

4 Check Pair (4): Exonucleases - Remove nucleotides from the ends of DNA, whereas Endonucleases cut at specific internal positions -> False.

5 Option (1) is the correct pair.

🛡️

Why You Can 100% Trust This Shortcut: NCERT Biology · Biotechnology: Principles and Processes (Tools of Recombinant DNA Technology: The cut pieces of DNA are joined together with the help of DNA ligase. Restriction endonucleases make cuts at specific positions within DNA, whereas exonucleases remove nucleotides from ends).

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Enzymatic Tools in Recombinant DNA Construction

Genetic engineering utilizes precision biocatalysts with specific substrates and chemical actions: - DNA Ligases: Catalyze the formation of a covalent phosphodiester bond between the $3'\text{-OH}$ end of one DNA strand and the $5'\text{-phosphate}$ group of another, effectively joining/sealing two DNA molecules together. - DNA Polymerases: Catalyze the $5' \to 3'$ template-dependent condensation of deoxynucleoside triphosphates (dNTPs) to synthesize new complementary strands (not breaking DNA). - Helicases: Unwind and separate the complementary base-paired strands of duplex DNA by breaking hydrogen bonds (not nucleases). - Exonucleases: Hydrolyze phosphodiester bonds at the terminal ends ( $5'$ or $3'$ ) of a polynucleotide chain, removing one nucleotide at a time. - Endonucleases (Restriction Enzymes): Cleave phosphodiester bonds at specific internal recognition sites within the DNA molecule.

\begin{aligned} \textbf{DNA Ligase} &\implies \text{Catalyzes Phosphodiester Linkage } [\mathbf{Joins\,two\,DNA\,molecules}] \\ \textbf{Polymerase} &\implies \text{Synthesizes DNA Strands} \\ \textbf{Exonuclease} &\implies \text{Cuts from Ends of DNA} \\ \textbf{Endonuclease} &\implies \text{Cuts Internally within DNA} \end{aligned}

Step 2

Option Elimination Summary

Only pair (1) matches the enzyme with its genuine biochemical function.

⭐

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 A

✓ 100% Correct

Verdict & Scientific Reason:

Correct. DNA ligases seal nicks and join recombinant DNA molecules together.

💡

Why this is airtight: None. Direct recall of standard molecular cloning enzymes.

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Polymerases synthesize DNA; restriction endonucleases break DNA into fragments.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing polymerases with degradative nucleases.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Helicase unwinds and separates DNA strands; nucleases hydrolyze phosphodiester bonds.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing strand separation with phosphodiester cleavage.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Endonucleases cut within DNA; exonucleases remove nucleotides from the terminal ends.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing exonucleases (outer ends) with endonucleases (internal specific sites).

⚠️

NTA Trap Alert: Exo vs Endo Prefix Confusion Trap

Paper setters regularly swap the definitions of Exonuclease (cleaves from external ends) and Endonuclease (cleaves internal specific sites). Always check the prefix: "Exo" = External ends; "Endo" = Inside/within.

🛡️ How to avoid the -1 mark: Remember: Ligase = Links/Joins; Exo = Ends; Endo = Internal.

📖

Core NEET Syllabus Standard

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

Core Scientific Principle Tested:

"DNA ligases join two DNA molecules by forming phosphodiester bonds."

Syllabus Focus: Enzymes of Recombinant DNA Technology

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

Ready to attempt under real exam pressure?

Test your speed and accuracy in the authentic 180-minute timed NTA simulator.

Launch NEET 2020 CBT Test →

← Previous (Q.6) All Botany Questions Grid Next (Q.8) →

Vector Anatomy & Features (Ori, Selectable Marker, Cloning Site, Transformation)

View Solution →

Spotted a mistake in this solution? Report an error ([email protected])

⚖️ Legal & Fair Dealing Notice: Sourced from publicly released NEET 2020 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 2020 Botany Question 7 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ "Ligases = Ligate / Join; Nucleases = Cut / Hydrolyze"

Step-by-Step Rigorous Workflow & Mathematical Proof

Enzymatic Tools in Recombinant DNA Construction

Option Elimination Summary

360° Option Elimination Engine Key Feature

NTA Trap Alert: Exo vs Endo Prefix Confusion Trap

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — Biotechnology: Principles and Processes

Polymerase Chain Reaction (PCR) Steps & Primer Annealing

Plasmids: Nature and Function as Cloning Vectors

Differential Enzymatic Cell Wall Lysis (Lysozyme vs. Cellulase)

Vector Anatomy & Features (Ori, Selectable Marker, Cloning Site, Transformation)

Solve 4 NEET Questions a Day — One per Subject