1. Chapter 6 The structure of DNA and RNA

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

5. Purines and pyrimidines

6. Base tautomers

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

11. DNA is usually a right-handed double helix

12. The major groove is rich in chemical information

13. DNA strands can separate (denature) and reassociate

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

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

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

18. 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 base pairs, Lk = +1,000 (DNA is right-handed)
DNA in cells is negatively supercoiled
Linking difference △Lk = Lk- Lko

19. Relaxing DNA with DNAse I

20. Relaxed DNA

21. Supertwisted DNA: DNA in cells is negatively supercoiled

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

23. Schematic mechanism of action for topoisomerase I

24. DNA topoisomers can be separated by electrophoresis

25. Intercalation of ethidium inot DNA

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

27. Double helical characteristics of RNA
Hairpin
bulge
loop

30. RNA can fold up into complex tertiary structures

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