nucleic acid - first discovered by Friedrich Miescher 

• P. A. Levene - determined nucleic acids’ basic structure (5-carbon sugar, phosphate group, nitrogenous base)
  • believed that 4 types of nucleotides available in equal amounts, repeated
• purine - adenine or guanine
• pyrimidine - thymine (replaced by uracil in RNA) or cytosine
• nucleotide - DNA unit, each consists of 5-carbon sugar, phosphate group, base
  • phosphate/hydroxide groups allow nucleotides to attach in long chains
  • phosphodiester bond - holds nucleotides together
• Erwin Chargaff - showed that DNA didn’t just repeat itself
  • amount of adenine always equals amount of thymine
  • amount of cytosine always equals amount of guanine

3D shape of DNA - shaped like staircase wrapping around a common axis 

• Rosalind Franklin - used X-ray diffraction to analyze DNA
  • bombarded DNA w/ X-ray beam, diffraction shows shape of molecule
  • used DNA fibers to analyze shape
  • thought that DNA could have helix shape
• James Watson/Francis Crick - used Franklin ’s results before she published them
  • found that DNA made up of 2 chains of nucleotides, forming a double helix
• complementarity - sets of hydrogen bonds link together base pairs
  • adenine forms 2 hydrogen bonds w/ thymine
  • guanine forms 3 hydrogen bonds w/ cytosine
  • knowing the sequence of 1 strand gives the sequence of the other strand
• antiparallel configuration - 2 strands of DNA oriented in different directions
• collective energy from all the base pairs together makes DNA strand very stable