CHE 211 Study Guide - Final Guide: Nuclear Membrane, Deoxyribose, Guanine
Organic Chemistry 2: Molecular Genetics
Schematic Ribbon Diagram of DNA Double Helix
► In the early 1940s, biologists determined that DNA contained within a variety of
organisms have a specific structure relationship between bases
► They found that the percent of Adenine was equal to the percent of Thymine; and the
percent of Guanine was equal to the percent of Cytosine it was determined that the
different organisms varied in the number of bases they contained, one thing was
constant Adenine only paired with Thymine and Guanine only paired with Cytosine
► In 1953, James Watson and Francis Creek proposed that DNA was a double helix that
consist of 2 polynuleotide strands that wound about each other similar to a spiral stair
case; the hydrophilic sugar-phosphate backbone is similar to the handrails, while the
hydrophobic bases are arranged are arranged more like steps along the inside
► The two strands run in opposite directions, where one strand goes in 5’-3’ direction and
the opposite strand goes in 3’-5’ direction
► Each of the bases along one polynucleotide strand forms hydrogen bonds to a specific
base on the opposite DNA strand (Adenine forms hydrogen bonds only with Thymine,
and Guanine only forms hydrogen bonds with Cytosine)
► A-T and G-C pairs are known as complimentary base pairs; the specificity of the base
pairing is owing to the fact that Adenine and Thymine can form 2 hydrogen bonds, and
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