Q.6 Restriction enzymes that recognize the same nucleotide sequence but cleave at
different positions are called
(A) heterohypekomers
(B) isocaudomers
(C) isoschizomers
(D) neoschizomers
The correct answer is (D) neoschizomers.
Restriction enzymes that recognize the same nucleotide sequence but cleave at different positions within that sequence are neoschizomers, distinguishing them from other types like isoschizomers that cut identically.
Option Analysis
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(A) Heterohypekomers: This term does not exist in molecular biology literature related to restriction enzymes; it appears to be a distractor or misspelling with no defined meaning.
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(B) Isocaudomers: These enzymes recognize different nucleotide sequences but produce compatible sticky ends due to identical overhangs after cleavage, such as BamHI and BclI.
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(C) Isoschizomers: These recognize and cleave the exact same nucleotide sequence at the identical position, like SphI and BbuI both cutting CGTAC/G, though they may differ in optimal conditions or methylation sensitivity.
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(D) Neoschizomers: These match the question precisely—they recognize the same sequence but cleave at different sites, generating distinct ends; examples include SmaI (CCC/GGG) and XmaI (C/CCGGG).
Restriction enzymes that recognize the same nucleotide sequence but cleave at different positions play a key role in molecular biology, especially in recombinant DNA technology for CSIR NET Life Sciences exams. Known as neoschizomers, these enzymes offer flexibility in generating varied DNA fragments from identical recognition sites, aiding precise cloning and analysis. Understanding neoschizomers alongside isoschizomers and isocaudomers ensures mastery of restriction enzyme classification.
Key Definitions
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Neoschizomers: Bind identical DNA sequences but cut asymmetrically, like SmaI (blunt end at center) vs. XmaI (sticky end offset); ideal for overhang-specific ligations.
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Isoschizomers: Cut the same sequence identically, e.g., HpaII and MspI on CCGG (differing only in methylation tolerance).
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Isocaudomers: Different sequences yield same overhangs, e.g., NcoI (C/CATGG) and PagI produce compatible 5′-CATG-3′ ends.
Applications in Research
Neoschizomers enable tailored fragment ends without sequence changes, crucial for vector construction and gene mapping in plant biotechnology. They differ from isoschizomers, which serve as backups under varying buffer conditions. For CSIR NET aspirants, examples like KpnI (GGTAC/C) and Acc65I (G/GTACC) highlight quantitative genetics toolkits.
