Question

Why does RNA contain uracil and DNA contain thymine? Choose the ONE best answer to this question.

choose one or more of the options:
a. Loss of NH3 from cytosine generates uracil, which base pairs with thymine and cause damage in DNA. If deamination of thymine generated guanine, then this would not be a problem.
b. DNA damage can alter the nucleotide bases and cause mutations that cannot be repaired if the base is uracil since repair enzymes recognize thymine in DNA, not uracil.
b. Ultraviolet light cause thymine dimers to accumulate in DNA, therefore if uracil were present in DNA, then these uracil dimers would not be recognized by nucleotide excision repair.
c. Spontaneous cytosine deamination generates uracil, which base pairs with thymine during replication, and thereby converts a C-G base pair to a T-U base pair.
d. Uracil specifies RNA polymerization, and therefore, if uracil is inserted into DNA, then RNA polymerization will occur on DNA strands.
e. Spontaneous cytosine deamination generates uracil, which base pairs with adenine during replication, and thereby converts a G-C base pair to a A-T base pair.
f. RNA transcription base pairs U-T in the RNA with DNA, whereas this process base pairs A-T in the RNA with DNA. Therefore, if uracil were present in DNA, then U-A and A-U could not be distinguished.
g. None of these statements are correct.

Answer 1

The correct answer is option b.

Step-by-step explanation:

Destruction of DNA can change the nucleotide bases and lead to mutations, which cannot be treated if the base is uracil. As the enzymes that help in repair identifies thymine in DNA, not uracil. RNA refers to a molecule that can degrade quite easily as it needs to get produced spontaneously. On the other hand, the DNA molecule is resistant to degradation in the long-term.

This takes place with the help of thymine that offers protection to DNA from nucleases in the cell and inhibits mismatches at the time of duplication.