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DNA Metabolism

DNA Metabolism. A structure this pretty just had to exist. —James Watson, The Double Helix, 1968. INFORMATION PATHWAYS. GENES AND CHROMOSOMES.

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DNA Metabolism

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  1. DNA Metabolism A structure this pretty just had to exist. —James Watson, The Double Helix, 1968

  2. INFORMATION PATHWAYS

  3. GENES AND CHROMOSOMES DNA topoisomerases are the magicians of the DNA world. By allowing DNA strands or double helices to pass through each other, they can solve all of the topological problems of DNA in replication, transcription and other cellular transactions. —James Wang, article in Nature Reviews in Molecular Cell Biology, 2002 Supercoiling, in fact, does more for DNA than act as an executive enhancer; it keeps the unruly, spreading DNA inside the cramped confines that the cell has provided for it. —Nicholas Cozzarelli, Harvey Lectures, 1993

  4. Genes Are Segments of DNA That Codefor Polypeptide Chains and RNAs

  5. DNA Molecules Are Much Longer Than the Cellular Packages That Contain Them

  6. DNA Molecules Are Much Longer Than the Cellular Packages That Contain Them

  7. A dividing mitochondrion. Some mitochondrialproteins and RNAs are encoded by one of the copies of the mitochondrial DNA (none of which are visible here). The DNA (mtDNA) isreplicated each time the mitochondrion divides, before cell division

  8. DNA, Gene, and Chromosome Content in Some Genomes

  9. Eukaryotic Genes and Chromosomes Are Very Complex

  10. Types of sequences in the human genome

  11. Important structural elements of a yeast chromosome

  12. DNA Supercoiling

  13. Supercoiling induced by separating the strands of a helical structure

  14. Relaxed and supercoiled plasmid DNAs

  15. Visualization of topoisomers

  16. The relations between the linking number (Lk), twisting number (Tw), and writhing number (Wr) of a circular DNA molecule revealed schematically

  17. Helical Twist and Superhelical Writhe Are Correlated with Each OtherThrough the Linking Number

  18. Lk is merely the number of crosses a single strand makes across the other . Lk, known as the "linking number", is the number of Watson-Crick twists found in a circular chromosome in a (usually imaginary) planar projection. This number is physically "locked in" at the moment of covalent closure of the chromosome, and cannot be altered without strand breakage. • The topology of the DNA is described by the equation below in which the linking number is equivalent to the sum of TW, which is the number of twists or turns of the double helix, and Wr which is the number of coils or 'writhes'. If there is a closed DNA molecule, the sum of Tw and Wr, or the linking number, does not change. However, there may be complementary changes in TW and Wr without changing their sum.

  19. - Type I Topoisomerases Relax Supercoiled Structures- Type II Topoisomerases Can Introduce Negative Supercoils Through Coupling to ATP Hydrolysis

  20. The Structure of Chromosomes

  21. Histones Are Small, Basic Proteins (Nucleosomes)

  22. Nucleosomes Are the Fundamental OrganizationalUnits of Chromatin

  23. Types and Properties of Histones

  24. Chromatin assembly

  25. The 30 nm fiber, a higher-order organization of nucleosomes

  26. Nucleosomes Are Packed into SuccessivelyHigher Order Structures

  27. Double-Helical DNA and RNA Can Be Denatured

  28. Map of the E. coli chromosome

  29. DNA Replication Follows a Set of Fundamental Rules • DNA Replication Is Semiconservative • Replication Begins at an Origin and Usually Proceeds Bidirectionally • DNA Synthesis Proceeds in a 5n3 Direction and Is Semidiscontinuous

  30. DNA Replication Is Semiconservative

  31. Replication Begins at an Origin and Usually Proceeds Bidirectionally

  32. DNA Synthesis Proceeds in a 5n3 Direction and Is Semidiscontinuous

  33. DNA Is Synthesized by DNA Polymerases

  34. DNA Is Synthesized by DNA Polymerases

  35. Replication Is Very Accurate

  36. E. coli Has at Least Five DNA Polymerases

  37. DNA polymerase III

  38. Subunits of DNA Polymerase III of E. coli

  39. DNA Replication Requires Many Enzymesand Protein Factors

  40. Arrangement of sequences in the E. coli replicationorigin, oriC

  41. Model for initiation of replication at the E. coli origin, oriC

  42. Proteins Required to Initiate Replication at the E. coli Origin

  43. Synthesis of Okazaki fragments

  44. DNA synthesis on the leadingand lagging strands

  45. Final steps in the synthesis of lagging strand segments

  46. Proteins at the E. coli Replication Fork

  47. Termination of chromosome replication inE. coli

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