Nucleic acids and chromatin
Nucleic acids and chromatin

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Summary of Section 3

  1. Watson–Crick base pairing arises due to hydrogen bonding between A and T and G and C and spatial limitations within the hydrophobic core of the helix.

  2. DNA commonly folds into the B-form helix; other forms such as Z-DNA form in vitro. A-form helices are formed primarily by duplex RNA.

  3. The twisting of DNA around its helical axis results in torsional stresses that promote the formation of high-energy alternative conformations such as supercoils.

  4. DNA chains accommodate changes in DNA twist through alterations in their supercoiling.

  5. Naturally occurring B-DNA is negatively twisted, a state that facilitates strand separating activities of DNA metabolism.

  6. Enzymes called DNA topoisomerases are responsible for managing torsional stress in DNA.

  7. Unusual DNA structures can form due to Hoogsteen bond formation between bases and are believed to occur in quadruplex and triplex DNAs.

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