## Molecules Cells

### Instructions

Write two functions:

- `RNA` that given a DNA strand it must return is complement RNA strand
- `DNA` that given a RNA strand it must return is complement DNA strand (invert RNA)

Since both strands are a sequence of nucleotides. It will be given the four nucleotides and its complements

```
DNA | RNA
 G  -  C
 C  -  G
 T  -  A
 A  -  U
```

Each strand must be represented as upper case string, without spaces, ex: `'ATCG'` is a valid DNA strand.