# What nucleic acid contains uracil?

Sep 5, 2016

RNA

#### Explanation:

Ribonucleic acid (RNA) is the nucleic acid that contains uracil.

The nucleotide called thymine in DNA is replaced by uracil in all types of RNA. These nucleotides are very similar in structure:

They only differ in one methyl ($C {H}_{3}$) group and both pair with the nucleotide adenine.

$\textcolor{red}{\text{Why did the cell change the strategy?}}$
This is a major question of course, why not use uracil in DNA? or why not thymine in RNA?

It has to do with two main things:

1. Stability: while uracil usually pairs with adenine, it can also pair with other nucleotides or with itself. This doesn't happen with thymine. DNA with thymine is therefore more stable = useful because it has to be passed on to the offspring.

2. Efficient repair: the nucleotide cytosine can easily turn into uracil. The repair mechanism of DNA can recognize and repair this. This wouldn't be possible when uracil was normally present in DNA.

It appears that uracil turned into thymine during evolution to make DNA more stable. Since RNA is only transiently present in the cell, uracil is apparently acceptable for nature in this nucleic acid.