Nucleic acids "will perhaps deserve equal consideration with the proteins."

The Discovery of Nucleic Acids: In 1868, Friedrich Miescher isolated a new substance from nuclei of cells from hospital bandages. He realized that this material, which he called nuclein, was a new class of organic material. It contained C, H, and O (like all organics), plus N (like the proteins). However, he knew it was not protein since it had no S and also had P. Furthermore, pepsin, which digests proteins, had no effect on nuclein. The nuclein Miescher isolated was probably a mixture of DNA and RNA. Today, instead of nuclein, we call this class of organic chemical the nucleic acids.

DNA Is the Genetic Material (of almost everything): In 1944, Avery, MacLeod, and McCarty showed that DNA was the genetic material of a bacterium (Streptococcus pneumoniae) that causes a type of pneumonia in mice. This experiment was based on the 1928 experiment of Griffith where he showed that some substance from dead IIIS bacteria (S cells have a capsule) could transform live IIR bacteria (R cells lack a capsule) into live IIIS cells. Avery et al. showed that Griffith's "transforming principle" was IIIS DNA. (A 1952 experiment by Hershey and Chase with the phage T2 showed that this virus' genetic material was DNA. Some DNA viruses have single-stranded DNA and some have double-stranded DNA.) Mutagenesis experiments also indicated that DNA was the genetic material of eukaryotes (this was later proved directly).

RNA Is the Genetic Material of Some Viruses. Some viruses have no DNA in the virus particle, but do have RNA. In these viruses, the RNA (which may be single stranded or double stranded) is the genetic material. Some RNA viruses replicate their RNA (similarly to the way DNA is replicated but using RNA replicase) while others use the enzyme reverse transcriptase to make a DNA intermediate which is then copied into new RNA. These viruses are called retroviruses.

DNA Structure: DNA is a polynucleotide (polymer of nucleotides). (Arsenic-based life finding fails follow-up)

• Specific Base Pairing: Base pairing holds an A of one strand to a T of the other strand and a G of one strand to a C of the other strand. This base pairing is by hydrogen bonding involving N, O, and H. There are three bonds that hold guanine to cytosine and two that hold adenine to thymine. (PBS video).

• The Dimensions of the Double Helix: The bases are 3.4 thick and stacked internally (i.e., the "distance between the bases" is 3.4 ). The width of the molecule is 20 and it makes one complete turn (360^○) every 34 of length. There are 10 base pairs per turn of the helix. (1mm=1000 μm, 1 μm=1000 nm, 1 nm=10 angstra)(angstrom = )(3-D DNA Viewer)(DNA)