From the start codon through the stop codon, the length of the fully processed AURKA mRNA is 1,212 nucleotides. Calculate the number of amino
acids in the polypeptide chain coded for by the mRNA.

404 amino acids  

Explanation:

The translation is the process by which a messenger RNA (mRNA) molecule is used as a template to synthesize a protein in the ribosomes. During translation, each triplet of nucleotides or 'codon' determines one specific amino acid of the growing polypeptide chain (i.e., the protein). In this case, the length of the fully processed AURKA mRNA consists of 1,212 nucleotides, thereby the length of the polypeptide chain will be 404 amino acids (protein length = 1,212 / 3 = 404 amino acids).

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.