Explain the right-handed rule, with thumb pointing parallel to axis of symmetry and fingers curved in direction of helical twist. When Watson and Crick looked at their model for the structure of the double helix in 1953, it immediately suggested to them how DNA replicates. In each round of replication each of the two strands of DNA is used as a template for the formation of a complementary DNA strand. The original strands, but not the original double helix, remain intact through many cell generations. Draw on board a short sequence of dsDNA and show how Chargaff's rules are used to make exact copies of the strands.
All nucleotides have a common structure.
The 2'-OH group in ribose makes RNA more reactive chemically than DNA, resulting for example in the hydrolysis of the phosphodiester bonds in RNA placed in basic or alkali solutions. The 2'-OH group is also involved in the enzymatic activity of certain RNA molecules called ribozymes. The chemical structures of the principal bases in nucleic acids. Know which ones are purines and which ones are pyrimidines, which ones are found in DNA and which ones in RNA, and be able to associate the structures of these N bases with their names. This figure is a particularly good example of the fact that the ends of the DNA molecule are chemically distinct and the meaning of the 5' to 3' directionality of the chain.