Answer:
Uracil
Explanation:
Like DNA, RNA is made up of nucleotides called ribonucleotides. However, unlike DNA, RNA contains the sugar ribose instead of deoxyribose and the base uracil instead of thymine. RNA also contains of only one polynucleotide chain. Uracil is a type of nitrogenous base that is replaced by thymine during the formation of RNA.
Uracil base is normally used in the synthesis of RNA but not in the synthesis of DNA. Uracil is found in RNA instead of Thiamine. Thiamine , on the other hand, is found in DNA and not in RNA.
Explanation:
It is believed that RNA preceded DNA in early life forms as the main storage of genetic code. RNA was not stable, however. Life form evolved a more stable form of genetic storage in the form of DNA. Nucleotide bases are easily deaminated, and especially Cytosine, to Uracil. Therefore DNA evolved the more stable form of the base called Thiamine (which is stable than Uracil). Therefore if Cytosine gets deaminated in DNA into Uracil, it can be easily recognized as a defect by repair mechanisms and repaired back to Cytosine, because DNA is not required to have Uracil.
Since RNA has a relatively short life span compared to DNA, it still retains Uracil because any damage, by photochemical mutations, will not last long as they would if they occurred on DNA.
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