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
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