What molecular structure serves as a code for the arrangement of proteins?

The correct answer is DNA, as it serves as the molecular structure that encodes the genetic information necessary for the synthesis of proteins. In essence, DNA contains the sequences of nucleotides (adenine, thymine, cytosine, and guanine) that constitute genes. Each gene corresponds to a specific sequence that dictates the order of amino acids in a protein, thus determining its structure and function.

This genetic blueprint is transcribed into RNA during a process called transcription, where the information in DNA is copied to produce messenger RNA (mRNA). The mRNA is then translated into a polypeptide chain during the process of translation, which ultimately folds into a functional protein. However, RNA itself does not serve as the original code; instead, it acts as a mediator that translates the DNA code into proteins.

In contrast, peptide chains are the result of the translation and represent the actual building blocks of proteins, not the code that dictates their arrangement. Fatty acids are components of lipids and do not contribute to protein coding. Thus, understanding that DNA encapsulates the instructions for protein assembly is crucial in molecular biology and genetics.