Final answer:
The analogy correctly completed is 'Nitrogenous bases are to nucleotides as side chains are to amino acids.' They both provide the necessary variation in the molecular structures for their respective polymers, nucleic acids and proteins.
Step-by-step explanation:
Nucleic acids are to nucleotides as side chains are to amino acids. The correct answer is c. nitrogenous bases. Just like side chains are the variable part attached to the main structure of amino acids, nitrogenous bases are attached to the sugar molecule in nucleotides, providing the variability necessary for encoding genetic information.
Nucleic acids, including DNA and RNA, are made up of monomers known as nucleotides. Each nucleotide consists of three parts: a nitrogenous base, a pentose (five-carbon) sugar, and a phosphate group. The phosphate group and sugar form the backbone of the DNA or RNA strand, much like the main chain of an amino acid, while the nitrogenous bases, like side chains, determine the properties and genetic coding of the nucleic acid.