Final answer:
The replacement of cytosine with adenine disrupts normal base pairing in DNA, leading to a bulge in the DNA structure and reducing the stability of the DNA helix. Such a mutation may alter the DNA's optimal width, hinder proper function, and compromise the integrity of genetic information.
Step-by-step explanation:
Impact of Adenine Replacement of Cytosine on DNA Structure
When an adenine replaces a cytosine in DNA, there is a disruption in the base pairing that is critical for the stability of the DNA double helix structure. Under normal circumstances, base pairing occurs between a purine and a pyrimidine, specifically adenine with thymine and guanine with cytosine. These pairings allow for the optimal width of the DNA helix and are stabilized by hydrogen bonds. Adenine-thymine pairs form two hydrogen bonds, and cytosine-guanine pairs form three, contributing to the DNA's stability.
Introducing adenine in place of cytosine disrupts this careful balance, as adenine would seek to pair with thymine rather than guanine, which typically pairs with cytosine. This inaccurate pairing may lead to a bulge in the DNA structure ('b' in provided options) where the inappropriate adenine is located because purine-purine pairing (like adenine with guanine) changes the helix's width, resembling a staircase with stair widths that are not uniform. Ultimately, this mutation disrupts the overall stability of the DNA molecule and may impair its function.