Two main differences between DNA and RNA are:
1. **Sugar Molecule**: DNA contains deoxyribose sugar, while RNA contains ribose sugar. The difference lies in the presence of an additional oxygen atom in the ribose sugar of RNA.
2. **Bases**: DNA contains adenine (A), thymine (T), cytosine (C), and guanine (G), while RNA contains adenine (A), uracil (U), cytosine (C), and guanine (G). The key distinction is that DNA uses thymine (T), whereas RNA uses uracil (U).
Base pairing:
- In DNA, adenine (A) pairs with thymine (T) via two hydrogen bonds, and cytosine (C) pairs with guanine (G) via three hydrogen bonds.
- In RNA, adenine (A) still pairs with uracil (U) via two hydrogen bonds, and cytosine (C) pairs with guanine (G) via three hydrogen bonds.
So, the base pairing rules in DNA are A-T and C-G, while in RNA, they are A-U and C-G.
