One of the most common spontaneous lesions that occurs in DNA under physiological conditions is the hydrolysis of the amino group of cytosine, converting the cytosine to uracil. What would be the effect on DNA structure of a uracil group replacing cytosine?

Verified step by step guidance

1. Understand that cytosine normally pairs with guanine in DNA through three hydrogen bonds, maintaining the DNA double helix structure.
2. Recognize that when cytosine undergoes deamination, it is converted into uracil, which is not a normal base in DNA but is normally found in RNA.
3. Consider that uracil pairs preferentially with adenine through two hydrogen bonds, unlike cytosine which pairs with guanine.
4. Analyze how the presence of uracil in DNA would lead to a mismatch during DNA replication, potentially causing a C-G to T-A transition mutation if not repaired.
5. Conclude that the incorporation of uracil disrupts the normal base pairing and can lead to mutations, which is why cells have repair mechanisms like uracil-DNA glycosylase to remove uracil from DNA.

Key Concepts

Spontaneous DNA Lesions and Deamination

Spontaneous DNA lesions are natural chemical changes that occur without external influence. Deamination is the removal of an amino group from a base, such as cytosine converting to uracil, which alters the base's identity and can lead to mutations if unrepaired.

Base Pairing and DNA Structure

DNA structure relies on specific base pairing: cytosine pairs with guanine via three hydrogen bonds. Replacing cytosine with uracil disrupts this pairing because uracil pairs with adenine, potentially causing mismatches and destabilizing the double helix.

DNA Repair Mechanisms for Uracil

Cells have repair systems like base excision repair to recognize and remove uracil in DNA, preventing mutations. Uracil-DNA glycosylase excises uracil bases, maintaining DNA integrity by restoring correct cytosine-guanine pairs.