Nucleic acids are polymers. What are the monomer units of nucleic acids?
To answer this question, let’s first look at the term nucleic acid. A nucleic acid is a large molecule that carries the genetic information essential for life. It includes DNA and the related molecule RNA. Here’s a drawing of a segment of DNA. DNA can be found in all living organisms. In eukaryotic cells, it can be found in the nucleus, which is where the word nucleic in nucleic acids comes from.
Now, let’s look more closely at the structure of this DNA molecule. For simplicity, let’s just focus on this part of the molecule that’s circled here. In black is what’s called the sugar phosphate backbone. This is made of a five-carbon sugar called deoxyribose that’s illustrated here as a pentagon and a phosphate group that’s illustrated here as a P with a circle around it. A nitrogenous base is attached to the deoxyribose sugar and is shown as a colored box here. Nitrogenous bases are often simply called bases. And in DNA, there are four of them: adenine, which can be abbreviated by the letter A; guanine; cytosine; and thymine.
The basic subunit of a nucleic acid, including the phosphate group, the deoxyribose sugar, and the base, is called a nucleotide. We can also call this nucleotide a monomer. This monomer can be linked together with other nucleotides to form a polymer that we can call a polynucleotide. Mono- in the word monomer means one, and poly- in the word polymer means many. Therefore, the monomer unit of a nucleic acid is a nucleotide.