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A tautomeric shift in DNA involves the repositioning of a proton within a molecule, leading to an alternative structural form of the nucleobase, which can alter its hydrogen bonding properties. This shift can result in a base pairing that deviates from the standard Watson-Crick model, potentially leading to mutations during DNA replication. Here’s the logic behind rejecting the wrong answers for the given options: A) It is always adenine that is changed - This is incorrect because tautomeric shifts can occur in all the nitrogenous bases (adenine, guanine, cytosine, and thymine/uracil), not just adenine. B) Final bonding of nucleotides remains unchanged - This is incorrect. Tautomeric shifts can change the hydrogen bonding properties of a base, potentially leading to mispairing with a different base than it would normally pair with. C) Adenine is changed so it can no longer form base pairs - This is incorrect. Tautomeric shifts do not prevent bases from forming base pairs; instead, they may cause a base to form an incorrect pair. D) Tautomeric shifts involve the relocation of hydrogen atoms within the molecule, leading to a change in the base's hydrogen bonding pattern. Problem: In a tautomeric shift (explain logic rejecting wrong answers) A) It is always adenine that is changed B) Final bonding of nucleotides remains unchanged C) Adenine is changed so it can no longer form base pairs D) Hydrogen atoms move to form a base with altered hydrogen properties E) Carbon atoms move to form a base with altered properties
