Q29.Chemically synthesized linker molecules containing recognition sequences of specific restriction endonucleases for creation of cohesive ends in blunt ended DNA fragments are generally
(A) 10 bp
(B) 24 bp
(C) 6 bp
(D) 20 bp
Chemically synthesized linker molecules for restriction endonucleases are generally 6 bp long, matching common recognition sites like EcoRI (GAATTC). This allows blunt-ended DNA to gain cohesive ends after ligation and digestion. Option (C) is correct.
Option Analysis
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(A) 10 bp: Too long for standard linkers; might fit rare 8-bp cutters but not typical ones.
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(B) 24 bp: Excessive; used for multi-site adapters or spacers, not basic cohesive-end creation.
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(C) 6 bp: Correct; aligns with frequent 6-bp palindromic sites (e.g., HindIII, BamHI).
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(D) 20 bp: Uncommon; possibly for synthetic oligos with extras, but not general linkers.
Introduction to Linker Molecules
Chemically synthesized linker molecules containing recognition sequences of specific restriction endonucleases enable blunt-ended DNA fragments to form cohesive ends. Typically 6 bp, they match enzymes like EcoRI. Essential for cloning vectors in molecular biology.
How Linkers Work
Linkers ligate to blunt DNA, then digestion exposes sticky ends. 6 bp suits Type IIP enzymes (4-8 bp sites, mostly 6 bp). Avoids self-ligation issues.
Why 6 bp Standard?
Most cloning enzymes recognize 6-bp palindromes; longer linkers add unnecessary cost/complexity. Commercial kits confirm this norm.
