go to ncbi:
- next to Send: click on the arrow.
- click on coding sequence
- make sure fasta nucleotide is checked
The most straight forward method is what Gabriel R. has suggested. The alternative, which allows documenting it at the same time, is to do so from the command line via Edirect.
esearch -db nucleotide -query "NM_033668.2" | efetch -format fasta_cds_na > cds_nm033668-2.fasta
You can use a software we have recently published I-PV (http://i-pv.org/). You will need perl and circos installed to be able to use it. It needs an mRNA sequence and a fasta file of your protein sequence ( the one that starts with NP_...). It will automatically generate a protein graph for your CDS. You can than compare each aminoacid and its codon...etc