Sometimes an error occurs and an adenine is paired to a cytosine. why is this interaction less stable than an adenine-thymine or cytosine-guanine base pair?

General
1

sometimes an error occurs and an adenine is paired to a cytosine. why is this interaction less stable than an adenine-thymine or cytosine-guanine base pair?

@aibot

2

Why is the pairing of adenine and cytosine less stable than adenine-thymine or cytosine-guanine base pair?

The stability of DNA base pairing is essential for the proper functioning of DNA replication and transcription processes. Adenine (A) and thymine (T), as well as cytosine (C) and guanine (G), form complementary base pairs with each other due to their specific hydrogen bonding patterns. However, when an error occurs and adenine pairs with cytosine instead of thymine, this base pairing is considered to be less stable for several reasons:

  1. Size mismatch: Adenine and cytosine have different sizes. Adenine is a larger base, while cytosine is smaller. This size disparity results in a misfit between the two bases when they try to form a pair. The size difference can lead to strain in the DNA double helix structure, destabilizing the overall DNA structure.

  2. Hydrogen bonding pattern: Adenine and cytosine form two hydrogen bonds when they pair together, while adenine-thymine and cytosine-guanine pairs form three hydrogen bonds each. The additional hydrogen bond in adenine-thymine and cytosine-guanine pairs contributes to a stronger interaction, increasing the stability of the DNA helix.

  3. Base stacking interactions: When DNA base pairs stack on top of each other in the double helix, they form favorable Van der Waals interactions. Adenine-thymine and cytosine-guanine pairs have favorable stacking interactions due to their structural compatibility, which further enhances the stability. In contrast, adenine-cytosine base pairs have less favorable stacking interactions, leading to decreased stability.

  4. Melting temperature: The melting temperature ™ is the temperature at which the DNA double helix separates during denaturation. It is influenced by the stability of base pairing. Adenine-thymine and cytosine-guanine pairs have higher Tm values compared to adenine-cytosine pairs, indicating higher stability and stronger base pairing.

Overall, the mispairing of adenine and cytosine introduces structural and energetic challenges, leading to a less stable interaction compared to adenine-thymine and cytosine-guanine base pairs.