The key difference between RNA and DNA in terms of their bases is the presence of uracil (U) in RNA instead of thymine (T) in DNA.

Here's a breakdown:

* DNA: The four bases in DNA are adenine (A), guanine (G), cytosine (C), and thymine (T).

* RNA: The four bases in RNA are adenine (A), guanine (G), cytosine (C), and uracil (U).

Therefore, the only difference in the bases involved is the substitution of thymine (T) with uracil (U) in RNA. This is a significant difference, as it impacts the overall structure and function of these two nucleic acids.

Here's a table summarizing the difference:

| Feature | DNA | RNA |

|---|---|---|

| Sugar | Deoxyribose | Ribose |

| Bases | Adenine (A), Guanine (G), Cytosine (C), Thymine (T) | Adenine (A), Guanine (G), Cytosine (C), Uracil (U) |

| Structure | Double helix | Single strand (usually) |

| Function | Stores genetic information | Carries genetic information and involved in protein synthesis |

It's important to note that uracil and thymine are very similar in structure, both being pyrimidine bases. This similarity is likely why they can substitute for each other in the context of RNA and DNA.