Final answer:
Tautomeric shifts are chemical rearrangements in DNA bases that can lead to temporary mispairing and, if not repaired, result in mutations such as transversion mutations. These shifts pose a threat to the fidelity of DNA replication and transcription and can be caused by spontaneous or induced damage.
Step-by-step explanation:
Tautomeric Shifts and Their Possible Effect on DNA
Tautomeric shifts refer to the chemical rearrangement of atoms within a molecule, leading to different isomeric forms known as tautomers. In the context of DNA, this shift commonly involves the movement of hydrogen and a switch between double and single bonds, especially among the nitrogenous bases adenine, cytosine, guanine, and thymine. Such shifts can lead to mispairing during DNA replication because the tautomeric form may form hydrogen bonds with a different base than expected. For example, in the keto-amino form, guanine pairs with cytosine, but in its rare enol-imino form, it may mistakenly pair with thymine, which is an error known as a transversion mutation.
These tautomeric shifts can be caused by spontaneous damage to DNA or induced by external factors such as UV damage, alkylation/methylation, X-ray exposure, and oxidative damage. In addition to potentially causing tautomerization, some chemicals act as mutagens by causing other modifications to DNA, such as the formation of thymine dimers, which can disrupt replication and result in point or frameshift mutations.
In biological systems, tautomeric shifts are transient and often corrected by DNA repair mechanisms. However, if not corrected, they can lead to permanent mutations, potentially contributing to genetic diseases and cancer. The fidelity of the template strand during DNA replication and transcription is crucial for maintaining genetic stability, and tautomeric shifts pose a threat to this fidelity.