What determines the order of amino acids in a polypeptide?

The order of amino acids in a polypeptide is determined by the sequence of RNA nucleotides in mRNA. This process begins with DNA being transcribed into mRNA, where each group of three nucleotides, known as a codon, corresponds to a specific amino acid. During translation, ribosomes read the mRNA sequence and assemble the polypeptide chain according to the codons, linking the appropriate amino acids together in the precise order dictated by the mRNA.

In this context, RNA nucleotides function as the template that encodes genetic information, which is then translated into the functional components of proteins. The correct sequence is crucial because even a slight change can lead to significant alterations in the resulting protein’s structure and function, potentially affecting the organism's overall biology. The other options relate to genetic regulation and chromatin structure, but they do not directly determine the primary structure of proteins as encoded by mRNA.