I was wondering why codons have 64 possible combinations when only 31 tRNA's are used? Are the other 33 possible combinations used for something else completely different from protein production? I understand wobble and why there are only 31 tRNAs, but don't really understand why DNA goes through the trouble of having 4 different bases and 3 bases per codon to create 64 possible sequences if only 31 sequences are needed in the first place. Thanks.
ALL codons are used. (Stop codons are used, but have no corresponding tRNA's). Both UUU and UUA are used, but same tRNA reads them. (It's not that UUU is used and UUA isn't). But why bother to have extra codons? We don't really know, but can guess. We assume it is easier to read/translate a code where all codons are the same length. If codons are 2 bases long, can't encode 20 different aa's. So codons need to be 3 bases long. But that provides extras. Either "the waste is worth it" in ease of translation, or more likely, having the extra codons acts as a "buffer" to reduce effects of mutations (mistakes). Many mistakes in a codon --> synonymous codon or a codon coding for a similar amino acid. So it looks like there has been selection for a code that is relatively easy to translate and minimizes the effects of errors.