Identify the key structural features of a DNA molecule
 a. DNA strands are antiparallel and include a 5'end and a 3'end.
 b. Strong ionic bonds and hydrophobic interaction hold DNA together. 
 c. DNA contains the nucleotide bases adenine, thymine, guanine, cytosine, and uracil. 
 d. DNA is most often found as a left-handed helix, commonly referred to as Z-DNA. 
 e. The backbone of DNA is made of a sugar and a phosphate molecule. 
 f. DNA bases are always paired purine with pyrimidine.