The entire thing is so unimaginably complex. For example, for a lot proteins that are catalysts (aka enzymes) the actual catalytic part is a metal ion and the protein mostly provides scaffolding. A nucleotide sequence alone doesn't directly tell you what ion is needed. In some cases, multiple ions can fit, but only one actually results in the protein work. This the basis for how a lot of toxic metal exert their toxic effects.
It's also not as simple as a nucleotide sequence codes for a protein and that's it. Proteins fold into their final shape from the chain of amino acids that DNA encodes. Protein folding in general is a hard problem. Biological proteins may have other proteins (called chperonins) that help them fold into their proper configuration. Then proteins may also be modified after they've folded (again by other proteins). Some proteins are made up of multiple sub-units as well.