Uracil

Explanation

Uracil is found in RNA, the DNA-like molecule involved in copying genetic information for translation (mRNA) as well as making up several of the participants in translation (tRNA, rRNA). Its pairing partner is adenine, with which it forms two hydrogen bonds.

• Https://thinkbio.guru/Swyde Images/AU.jpg

  Uracil (right) shown in pairing orientation with adenine (left). The red and blue halos represent partial negative (red) and positive (blue) charges that lead to base pairing.

Uracil is noteworthy because it's the 'different' base between DNA and RNA. In DNA, adenine's partner is thymine, taking the place of uracil. There are many misconceptions about the likely reason uracil was replaced by DNA. The first point to notice is that uracil and thymine are identical in their partnering interactions with adenine, and neither is meaningfully more stable as a chemical. Why, then, did evolution 'switch' to the use of thymine for every DNA-using organism we know of? The answer is a bit complicated; it actually starts with cytosine. Cytosine can undergo a very common chemical reaction with water that results in changes to two of its basepairing positions. However the shortest summary of what happens is that this reaction changes cytosine to uracil