Deoxyribonucleic acid, more commonly called DNA, is the molecule used by cells for storing, transferring, and expressing genetic information. It provides the instructions – much like a recipe – for everything that makes an organism what it is. If proteins are the building blocks for various structures and enzymes in the cell, the DNA is the recipe that tells the cell how to create these building blocks.
The monomer, or most basic subunit of nucleic acid is the nucleotide. Nucleotides are composed of a nitrogenous base, a phosphate group, and a sugar (deoxyribose, in the case of DNA). The phosphate group and the nitrogenous base are both connected to the sugar. If the nucleotide is a part of a polynucleotide chain, it is typically referred to as being the base.
A polynucleotide chain is just a long chain of nucleotides. The word “poly” simply means “many.” The nucleotides that are present in the polynucleotide molecule are held together through the bond that is present between the sugar of one nucleotide and the phosphate group of another. The hydroxyl group (-OH) that is in the sugar and one of the atoms of oxygen that is in the phosphate group work to form what is referred to as the diester bond. Because of this, the bond formed between the sugar and phosphate group in the polynucleotide molecule is referred to as the phosphodiester bond.
When nucleotides are linked together, a structure is formed. This structure looks much like half of a ladder split down the middle. The sugars and the phosphate groups create the ladder’s backbone, and the nitrogenous bases are what create the ladder’s rungs.