DNA & DNA STRUCTURE

1. DNA & DNA STRUCTURE YILDIRIM BEYAZIT UNIVERSITY FACULTY OF MEDICINE THE DEPARTMENT OF MEDICAL BIOLOGY ASST. PROF. DR. ENDER ŞİMŞEK

2. Timeline 1800’s F. Miescher- Nucleic Acids 1928 F. Griffith - Transforming Principle Avery, MacLeod& McCarty - Transforming Principle (DNA, the Genetic Material) 1944 Hershey & Chase - “Blender” Experiment 1952 Erwin Chargaff - Base Ratios 1952 Franklin & Wilkins- DNA Diffraction Pattern 1952 J. Watson and F. Crick - DNA Structure 1953

3. Before DNA was known as the genetic material in cells, scientists knew that: • there was a connection between chromosomes and inherited traits,

4. Before DNA was known as the genetic material in cells, scientists knew that: • there was a connection between chromosomes and inherited traits, • the genetic material had to control the production of enzymes and proteins,

5. Before DNA was known as the genetic material in cells, scientists knew that: • there was a connection between chromosomes and inherited traits, • the genetic material had to control the production of enzymes and proteins, • the genetic material had to be able to replicate itself with accuracy and still allow mutations to occur.

6. Scientists, now, know that DNA carries genetic information that defines many of an organism’s traits (including behaviours) and its predisposition for certain diseases.

7. Thus, the following experiments showed that the hereditary material in living organisms is DNA. • Frederick Griffith’s experiments • Oswald Avery’s experiments • Hershey and Chase’s experiments

8. Identifying DNA as the Material of Heredity!..

9. Frederick Griffith’s experiments with Streptococcus pneumoniae in 1928 Two forms of the bacterium were used: • The S-strain was highly pathogenic but could be made non-pathogenic by heating it. • The R-strain was non-pathogenic.

10. Griffith discovered that mice died after being injected with a mixture of heat-killed S-strain and living R-strain bacteria. Griffith called this phenomenon the transforming principle because something from the S-strain transformed the R-strain into deadly bacteria.

12. Griffith’s experiment showed that a chemical subdstance from one cell is capable of genetically transforming another cell but they didn’t know that DNA is the genetic material yet.

13. Canadian-American microbiologist Oswald Avery and his group built on Griffith’s work to identify the molecules in the S-strain that caused the transformation.

14. Canadian-American microbiologist Oswald Avery and his group built on Griffith’s work to identify the molecules in the S-strain that caused the transformation. Avery, MacLeod, and McCarty prepared identical extracts of the heat-killed S-strain and subjected each extract to one of three enzymes: • one that destroyed proteins, • one that destroyed RNA, and • one that destroyed DNA.

15. Each enzyme treated extract was then mixed with live R-strain cells.

16. The only extract that did not allow transformation of the R-strain to the pathogenic S-strain was the one treated with the DNA-destroying enzyme.

17. The only extract that did not allow transformation of the R-strain to the pathogenic S-strain was the one treated with the DNA-destroying enzyme. Therefore, Avery and his colleagues concluded that DNA was the hereditary material.

18. In 1952, Alfred Hershey and Martha Chase ruled out protein as the hereditary material. Hershey and Chase used two different radioactive isotopes to track each molecule (35S for proteins and 32P for DNA). They worked with T2 bacteriophages, which consist of nucleic material surrounded by a protein coat.

19. The bacteriophageswith DNA radioactively labeled with 32P was allowed to infect bacteria. After agitation and separation, radioactivity was found in the bacteria pellet but not in the liquid medium. In their first experiment:

20. In their second experiment: • The bacteriophages with its protein coat radioactively labeled with 35S was allowed to infect bacteria. After agitation and separation, radioactivity was found in the liquid medium but not in the bacteria pellet.

21. Hershey and Chase’s Experiments

24. Thus, the results proved that DNA, not protein, enters bacterial cells and is the genetic material.

25. Determining the Chemical Composition and Structure of DNA DNA was discovered in 1869 by FredrichMiescher. By isolating the nuclei of white blood cells, Miescherextracted an acidic molecule called asnuclein.

26. Determining the Chemical Composition and Structure of DNA DNA was discovered in 1869 by FredrichMiescher. By isolating the nuclei of white blood cells, Miescherextracted an acidic molecule called asnuclein. In the early 1900s, Phoebus Leveneisolated two types of nucleic acid: RNA and DNA. In 1919, he proposed that both were made up of individual units called nucleotides.

27. Determining the Chemical Composition and Structure of DNA DNA was discovered in 1869 by FredrichMiescher. By isolating the nuclei of white blood cells, Miescherextracted an acidic molecule called asnuclein. In the early 1900s, Phoebus Levene isolated two types of nucleic acid: RNA and DNA. In 1919, he proposed that both were made up of individual units called nucleotides. Each nucleotide was composed of one of four nitrogen-containing bases, a sugar, and a phosphate group.

28. A nucleotide is made of 3 components: 1.APentose sugar. This is a 5 carbon sugar. The sugar in DNA is deoxyribose. The sugar in RNA is ribose. Structure of a nucleotide:

29. 2. A Phosphate group. Phosphate groups are important because they link the sugar on one nucleotide onto the phosphate of the next nucleotide to make a polynucleotide. Structure of a nucleotide:

30. 3. A Nitrogenous base. In DNA the four bases are: Adenine Guanine Cytosine Thymine Structure of a nucleotide:

31. Nucleotides: Phosphate Nitrogenous Base Pentose Sugar • Each nucleotide consists of: • Phosphate group • Pentose sugar • Nitrogenous base

32. Pyrimidines Thymine - T Cytosine - C Purines Adenine - A Guanine - G Nitrogenous bases: – Two types

33. In later years, other scientists confirmed Levene’s work. DNA and RNA are both made up of a combination of four different nucleotides. • DNA has the nucleotides adenine (A), guanine (G), cytosine (C), and thymine (T). • RNA has the nucleotides adenine (A), guanine (G), cytosine (C), and uracil (U).

34. DNA Nucleotides: • Each base will only bond with one other specific base. • Adenine (A) • Thymine (T) • Cytosine (C) • Guanine (G) Form a base pair. Form a base pair.

35. The general structure of a DNA nucleotide includes a phosphate group, a deoxyribose sugar group, and a nitrogen-containing base.

36. The general structure of a DNA nucleotide includes a phosphate group, a deoxyribose sugar group, and a nitrogen-containing base. Nucleotides in RNA have the same basic structure, except a ribose sugar group is used. The sugar groups differ by a hydroxyl group at the 2′ carbon.

37. The general structure of a DNA nucleotide includes a phosphate group, a deoxyribose sugar group, and a nitrogen-containing base. Nucleotides in RNA have the same basic structure, except a ribose sugar group is used. The sugar groups differ by a hydroxyl group at the 2′ carbon. Both DNA and RNA contain the same purine bases and the cytosine pyrimidine base. However, thymine is only present in DNA, and uracil is only present in RNA.

38. DNA Nucleotides: Adenine Adenine (A) base with a double-ring structure sugar (deoxyribose)

39. DNA Nucleotides: Guanine Guanine (G) base with a double-ring structure

40. DNA Nucleotides: Cytosine Cytosine (C) base with a single-ring structure

41. DNA Nucleotides: Thymine (T) Thymine base with a single-ring structure

42. Chargaff’s Rule: Erwin Chargaff was inspired by Avery, MacLeod, and McCarty’s work on DNA and launched a research program to study nucleic acids.

43. Chargaff’s Rule: Erwin Chargaff was inspired by Avery, MacLeod, and McCarty’s work on DNA and launched a research program to study nucleic acids. By the late 1940s, he had reached two conclusions: • There is variation in the composition of nucleotides in different species.

44. Chargaff’s Rule: Erwin Chargaff was inspired by Avery, MacLeod, and McCarty’s work on DNA and launched a research program to study nucleic acids. By the late 1940s, he had reached two conclusions: • There is variation in the composition of nucleotides in different species. • Regardless of the species, DNA maintains certain nucleotide proportions. That is, the amount of A and T nucleotides are equal and the amount of C and G nucleotides are equal. This constant relationship is known as Chargaff’s rule.

45. Figure 13.7 Chargaff’s Rule

46. Chargaff’s Rule: Closing in on the Structure of DNA In DNA, the percent composition of adenine is the same as thymine, and the percent composition of cytosine is the same as guanine.

47. Rosalind Franklin Determines a Helical Structure for DNA In the early 1950s, Rosalind Franklin and Maurice Wilkins used X-ray diffraction to analyze DNA samples. Franklin captured high-resolution photographs and, using mathematical theory to interpret them.

48. Rosalind Franklin Determines a Helical Structure for DNA In the early 1950s, Rosalind Franklin and Maurice Wilkins used X-ray diffraction to analyze DNA samples. Franklin captured high-resolution photographs and, using mathematical theory to interpret them. Franklin determined the following: • DNA has a helical structure. • The nitrogen bases are on the inside of the DNA helix, and the sugar-phosphate backbone is on the outside. (A) Rosalind Franklin was a British chemist who was hired to work alongside Maurice Wilkins at the X-ray diffraction facilities at King’s College. (B) In the diffraction image of DNA that she produced, the central x-shaped pattern enabled researchers to infer that DNA has a helical structure.

49. Watson and Crick Build a Three-Dimensional Model for DNA In the early 1950s, Watson and Crick began working on a description of the structure of DNA using the results and conclusions of their peers.

50. In 1953, they published a paper that proposed a structure with the following features: • a twisted ladder, which they called a double-helix. • The sugar-phosphate molecules make up the sides or “handrails” of the ladder, and the bases make up the “rungs” of the ladder by protruding inwards.