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Chapter 6 The structure of DNA and RNA

Chapter 6 The structure of DNA and RNA. DNA is composed of polynucleotide chain: the helical structure of DNA. Purines and pyrimidines. Base tautomers. The two chains of the double helix have complementary sequences. DNA is usually a right-handed double helix.

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Chapter 6 The structure of DNA and RNA

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  1. Chapter 6 The structure of DNA and RNA

  2. DNA is composed of polynucleotide chain: the helical structure of DNA

  3. Purines and pyrimidines

  4. Base tautomers

  5. The two chains of the double helix have complementary sequences

  6. DNA is usually a right-handed double helix

  7. The major groove is rich in chemical information

  8. DNA strands can separate (denature) and reassociate

  9. Dependence of DNA denaturation on G+C content and on salt concentration Low salt high

  10. Topological states of covalently closed, circular (ccc) DNA LK=Tw+ Wr Linking number is composed of twist and writhe

  11. Two forms of writhe of supercoiled DNA toroidal writhe interwound

  12. Lko is the linking Number of fully relaxed cccDNA under Physiological conditions • Lko for such a molecule is the number of base pairs divided by 10.5. • For a cccDNA of 10500 base pairs, Lk = +1,000 (DNA is right-handed) • DNA in cells is negatively supercoiled • Linking difference △Lk = Lk- Lko

  13. Relaxing DNA with DNAse I

  14. Relaxed DNA

  15. Supertwisted DNA: DNA in cells is negatively supercoiled

  16. Topoisomerases can relax supercoiled DNA Schematic for changing the linking number in DNA with topoisomerase II

  17. Schematic mechanism of action for topoisomerase I

  18. DNA topoisomers can be separated by electrophoresis

  19. Intercalation of ethidium inot DNA

  20. RNA contains ribose and uracil and is usually single-stranded

  21. Double helical characteristics of RNA Hairpin bulge loop

  22. RNA can fold up into complex tertiary structures

  23. Some RNAs are enzymes, known as ribozymes The hammerhead ribozyme cleaves RNA by the formation of a 2’, 3’ cyclic phosphate

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