Q75.Match List I with List II
| LIST I | LIST II |
|---|---|
| A. Type II restriction endonuclease | I. Removes nucleotides from 5′ ends of duplex DNA |
| B. DNA ligase | II. Removes nucleotides from the 3′ ends of a DNA strand |
| C. Exonuclease III | III. Cleaves DNA at specific base sequences |
| D. Bacteriophage λ exonuclease | IV. Joins two DNA molecules |
Choose the correct answer from the options given below:
(1) A-III, B-IV, C-II, D-I
(2) A-IV, B-III, C-II, D-I
(3) A-II, B-III, C-IV, D-I
(4) A-I, B-II, C-III, D-IV
Type II restriction endonucleases cleave DNA at specific sequences, while exonucleases like Exonuclease III and λ exonuclease remove nucleotides from DNA ends, and DNA ligase joins DNA strands. The correct match for Q75 is option (1): A-III, B-IV, C-II, D-I.
List I-II Breakdown
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A. Type II restriction endonuclease → III. Cleaves DNA at specific base sequences: These enzymes recognize palindromic sequences (4-8 bp) and cut within/near them (e.g., EcoRI at GAATTC).
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B. DNA ligase → IV. Joins two DNA molecules: Seals nicks between adjacent 3′-OH and 5′-phosphate ends, essential for cloning and replication.
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C. Exonuclease III → II. Removes nucleotides from the 3′ ends of a DNA strand: 3’→5′ exo activity on dsDNA, used in footprinting and sequencing prep.
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D. Bacteriophage λ exonuclease → I. Removes nucleotides from 5′ ends of duplex DNA: 5’→3′ exo specific for dsDNA ends, processes λ DNA for packaging.
Option Analysis
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(1) A-III, B-IV, C-II, D-I: Correct; matches standard enzyme functions—restriction enzymes cut internally at sites, ligase joins, Exo III is 3′ exo, λ exo is 5′ exo.
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(2) A-IV, B-III, C-II, D-I: Wrong; type II enzymes don’t join DNA (that’s ligase).
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(3) A-II, B-III, C-IV, D-I: Wrong; type II don’t act as 3′ exo, ligase doesn’t cleave.
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(4) A-I, B-II, C-III, D-IV: Wrong; type II aren’t 5′ exo (that’s λ exo).
Ace Match List I with List II questions on Type II restriction endonuclease, DNA ligase, Exonuclease III, and Bacteriophage λ exonuclease for CSIR NET Life Sciences, GATE Biotech, and CSIR UGC NET exams. This detailed guide solves Q75, defines each enzyme’s function (cleaves DNA specific sequences, joins DNA molecules, removes 3′/5′ nucleotides), analyzes all options, and provides exam strategies.
Enzyme Functions Defined
These are core recombinant DNA tools classified by action: endonucleases (internal cuts), ligases (joining), exonucleases (end removal).
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Type II restriction endonuclease: Cuts dsDNA at precise palindromic sites (e.g., 4-8 bp), Mg²⁺-dependent, no ATP needed.
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DNA ligase: Catalyzes phosphodiester bond formation between DNA fragments.
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Exonuclease III: Progressively digests dsDNA from 3′ ends (3’→5′ polarity).
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Bacteriophage λ exonuclease: Specifically degrades dsDNA from 5′ ends (5’→3′).
Correct Option: Why (1)?
Option (1) A-III, B-IV, C-II, D-I aligns perfectly—type II for sequence-specific cleavage, distinct exo polarities prevent mismatches.
Why Other Options Fail
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Option (2): Swaps A (not ligase) and B (not restriction).
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Option (3): Misassigns A to exo II, B to cleavage.
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Option (4): Confuses endonucleases with exonucleases.
Exam Tips for Enzyme Matching
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Remember polarities: Exo III (3′), λ exo (5′); type II always “specific sequences.”
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PYQ pattern: CSIR NET frequently tests restriction-modification systems.
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Mnemonic: “Type II Cuts Inside, Ligase Links, Exo III 3′, Lambda 5′.”
Master this Match List I List II Type II Restriction Endonuclease DNA Ligase Exonuclease III Bacteriophage λ Exonuclease for top scores—share and revise!
