When scientists discovered that chromosomes were composed of DNA and proteins, they believed that proteins were the material of genes, due to the large varieties found in their building blocks. Hershey and Chase showed that DNA was the genetic material of a virus called T2 that infected E. coli. T2 is a bacteriophage, or a virus that infects bacteria. They did this using an experiment that clearly showed that the virus injected its DNA into the host cell. This DNA caused the bacteria to change.

DNA and RNA are nucleic acids that are composed of nucleotides. A polynucleotide is a polymer that consists of nucleotides. Nucleotides consist of a nitrogenous base, a sugar and a phosphate group. Nucleotides are connected by covalent bonds between the sugar and phosphate molecules. This results in a sugar-phosphate backbone.

The four types of nucleotides in DNA differ only in their nitrogenous bases...