There are two main sources of uracil in DNA: deaminated cytosine and RNA primers from Okazaki fragments, which were accidentally left behind in DNA. Consider ONE uracil that resulted from cytosine deamination and ONE uracil that was left behind as part of RNA primer. Which one would be more likely to cause a mutation?

A. Uracil from cytosine deamination
B. Uracil from RNA primers
C. Both are equally likely

Explanation:

1. Uracil is one of the four nitrogen bases, it is found in normal RNA.

2. In case of some type of mutation, Uracil can be found also in DNA by result of enzymatic or non-enzymatic deamination of cytosine as well as misincorporation of dUMP instead of dTMP during DNA replication.

3. Uracil which is found in DNA can be removed by DNA repair enzymes with apirymidine site as an intermediate.

4. And, if uracil is not removed from DNA a pair C:G in parental DNA can be changed into a T:A pair in the daughter DNA molecule. If not removed Uracil in DNA may lead to a mutation.

5. Uracil in DNA is recognized by uracil DNA glycosylase (UDGs), which initiates DNA base excision repair,  and it leads to the removing of uracil from DNA and replacing it by thymine or cytosine, when it  arose as a result of cytosine deamination.  

6. while uracil form RNA primer .

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