DNA The Code of Life

2. DNAThe Code of Life The Molecular Basis of Inheritance

3. DNA Deoxyribonucleic acid The information necessary to sustain and perpetuate life is found within a molecule. This is the genetic material that is passed from one generation to the next---a blue print for building living organisms.

4. History Although we now accept the idea that DNA is responsible for our biological structure, But in the early 1800s it was unthinkable for the leading scientists and Philosophers that a chemical molecule could hold enough information to build a human. They believed that plants and animals had been specifically designed by a creator.

5. History Charles Darwin is famous for challenging this view. In 1859 he published 'The Origin of Species‘ expressing that living things might appear to be designed, but were actually the result of natural selection. Darwin showed that living creatures evolve over several generations through a series of small changes.

6. History In the 1860s Darwin's ideas were supported when genetics was discovered by Gregor Mendel. He found that genes determine the characteristics a living thing will take. The genes are passed on to later generations, with a child taking genes from both its parents. The great mystery was where and how is this information stored?

7. History The main conclusions made by Mandle were: *SEGREGATION: Inherited traits are controlled by genes, which are in pairs. When sex cells are created one gene from each pair goes into the gamete. When two gametes fuse at fertilization, the offspring has two copies of each gene—one from each parent. *INDEPENDENT ASSORTMENT: The genes for different traits are sorted into gametes independently of other genes. So one inherited trait is not dependent on another. *DOMINANCE: Where there are two different forms of a gene are present in a pea plant, the one which is dominant is the one that is observed.

8. History Search for genetic material: In 1870, a German scientist named Friedrich Miescher had isolated the chemicals found in the nucleus. These were proteins and nucleic acids. While he found these nucleic acids interesting, and spent a great deal of time studying their chemical composition, he wasn’t alone in believing that proteins were more likely to be the chemicals involved in inheritance, because of their immense variability. They were made up of 20 different building blocks (amino acids), as opposed to the mere 4 building blocks of nucleic acids.

9. History Search for genetic material: In the early 1900s, Phoebus Levene, who also believed that proteins must be the chemicals of inheritance, studied the composition of nucleic acids. He discovered that DNA is a chain of nucleotides, with each nucleotide consisting of a deoxyribose sugar, a phosphate group and a nitrogenous base, of which there were four different types. He proposed that the four different types of nucleotide were repeated over and over in a specific order. This would make DNA a relatively simple repeat sequence – no wonder DNA wasn’t considered to be smart enough to code for all of life!

10. History Search for genetic material: 1928 Frederick Griffith: transforming principle

11. History Search for genetic material: It wasn’t until 1944 that Oswald Avery and his colleagues, who were studying the bacteria which causes pnuemonia, Pneumococcus, discovered by process of elimination that bacteria contain nucleic acids, and that DNA is the chemical which carries genes. Despite the conclusive results of Avery’s experiments, the theory of nucleic acids being the genetic material was still not a popular one, but experiments Performed with viruses also showed that nucleic acids were the genetic material and this confirmed Avery’s work.

12. History Search for genetic material: 1952 -Hershey-Chase Experiment

13. History Search for genetic material: • Classic experiments for evidence Griffith: transformation Hershey-Chase: DNA necessary to produce more virus • Other supporting evidence DNA volume doubles before cells divide Chargaff: ratio of nucleotides A = T and G = C

14. The Discovery The DNA molecule was discovered in 1951 by Francis Crick, James Watson and Maurice Wilkins using X-ray Diffraction. In Spring 1953, Francis Crick and James Watson, two scientists working at the Cavendish Laboratory in Cambridge, discovered the structure of the DNA a double helix, or inter-locking pair of spirals, joined by pairs of molecules.

15. The Discovery The seed that generated this was Watson’s presence at a conference in Naples in 1951, where an x-ray diffraction picture from DNA was shown by Maurice Wilkins from King’s College in London. This made a strong impression on Watson – the first indicationthat genes might have a regular structure.

16. History Search for genetic material: James Watson joined the unit (its first biologist) and began by trying to crystallize myoglobin for Kendrew. The unsuccess of this left much time for discussion with Crick, whose office he was sharing, and the topic of DNA structure naturally arose – particularly how to determine it. They were inclined to follow the method of Pauling who had deduced the a-helical structure by building a model consistent with the x-ray patterns from fibrous proteins. Like proteins, DNA was built from similar units – the bases adenine (A) thymine (T) guanine (G) and cytosine (C), and so it seemed likely that DNA too had a helical structure. The publishedx-ray patterns of DNA were not very clear, and so contact was made with King’s. Watson attended a DNA colloquium there in November 1951, at which Rosalind Franklin described her results.

17. History Search for genetic material: Watson brought back a less-than-accurate account to Cambridge, but with Crick produced a three-strandmodel structure only a week later. Invited to view this,Franklin pointed out that it was inconsistent with her results – it had thephosphate groups on the inside whereas her results showed they were on the outside,and the water content was too low. The work at Cambridge stopped abruptly for a bit.

18. History Search for genetic material: In July 1952, Erwin Chargaff visited the unit and told of his 1947 findings that the ratios of A/T and G/C were unity for a wide variety of DNAs. Crick became convinced that base pairing was the key to the structure. Prompted by receiving a flawed manuscript on DNA structure from Pauling, Watson again visited King’s and Wilkins showed him a DNA x-ray pattern taken by Franklin of the pure B-form showing clear helical characteristics, plus the intense 10th layer line at 3.4A and a 20A equatorial reflection indicating the molecular diameter. Perutz also showed them a report on the work of the King’s group which gave the space group of the crystalline A-form as C2, from which Crick deduced that there were two chains running in opposite directions.

19. History Search for genetic material: Watson began pursuing the idea of hydrogen bonding using cardboard cutouts of the four bases. He found that (A+T) and (G+C) could be bonded together to form pairs with very similar shapes. On this basis a model was built consistent with the symmetry and with Chargaff’s results, and a paper was published in April 1953 in Nature accompanied by ones from the Wilkins and Franklin groups at King’s. Watson and Crick’s paper ends with the oft-quoted line “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material”.

20. The Evidence Search for genetic material: James Watson and Francis Crick used this photo with other evidence to describe the structure of DNA. X-ray diffraction photo of DNA Image produced by Rosalind Franklin

21. Watson and Crick with their DNA model

22. The Scientists Francis Crick was born in 1916. He went to London University and trained as a physicist. After the war he changed the direction of his research to molecular biology. James Watson was an American, born in 1928, so aged only 24 when the discovery was made. He went to Chicago University aged only 15 and had already worked on DNA.

23. The Nobel Prize Crick, Watson and Wilkins won the Nobel Prize for medicine in 1962. Maurice Wilkins was at King's College, London and was an expert in X-ray photography. His colleague, Rosalind Franklin, did brilliant work developing the technique to photograph a single strand of DNA. She received little recognition for this at the time and died tragically of cancer in 1958, so could not be recognised in the Nobel Award.

24. Watson & Crick What they deduced from: Franklin’s X-ray data • Double helix • Uniform width of 2 nm • Bases stacked 0.34 nm apart Chargoff’s “rules” • Adenine pairs with thymine • Cytosine pairs with guanine

25. Watson & Crick What they came up with on their own: • Bases face inward, phosphates and sugars outward • Hydrogen bonding • Hinted at semi-conservative model for replication

26. KEY PLAYERS Oswald Avery (1877-1955) Microbiologist Avery led the team that showed that DNA is the unit of Inheritance. One Nobel laureate has called the discovery "the historical platform of modern DNA research", and his work inspired Watson and Crick to seek DNA's structure.

27. KEY PLAYERS Erwin Chargaff (1905-2002) Chargaff discovered the pairing rules of DNA letters, noticing that A Matches to T and C to G. He later Criticized molecular biology, the discipline he helped invent, as "the practice of biochemistry without a licence",and once described Francis Crick as looking like "a faded racing tout".

28. KEY PLAYERS Francis Crick (1916- )Crick trained and worked as a physicist, but switched to biology after the Second World War. After co-discovering the structure of DNA, he went on to crack the genetic code that translates DNA into protein. He now studies consciousness at California's Salk Institute.

29. KEY PLAYERS Rosalind Franklin (1920-58) Franklin, trained as a chemist, was expert in deducing the structure of molecules by firing X-rays through them. Her images of DNA - disclosed without her knowledge - put Watson and Crick on the track towards the right structure. She went on to do pioneering work on the structures of viruses. .

30. KEY PLAYERS Linus Pauling (1901-94) The titan of twentieth-century chemistry. Pauling led the way in working out the structure of big biological molecules, and Watson and Crick saw him as their main competitor. In early 1953, working without the benefit of X-ray pictures, he published a paper suggesting that DNA was a triple helix.

31. KEY PLAYERS James Watson (1928- )Watson went to university in Chicago aged 15, and teamed up with Crick in Cambridge in late 1951. After solving the double helix, he went on to work on viruses and RNA, another genetic information carrier. He also helped launch the human genome project, and is president of Cold Spring Harbor Laboratory in New York.

32. KEY PLAYERS Maurice Wilkins (1916- )Like Crick, New Zealand-born Wilkins trained as a physicist, and was involved with the Manhattan project to build the nuclear bomb. Wilkins worked on X-ray crystallography of DNA with Franklin at King's College London, although their relationship was strained. He helped to verify Watson and Crick's model, and shared the 1962 Nobel with them.

33. Structure

34. Structure

35. Structure

36. Structure

37. Structure

38. Structure There are 4 different nucleotides in DNA Adenine pairs with Thymine Guanine pairs with Cytosine

39. Structure Adenine pairs with Thymine Guanine pairs with Cytosine

40. Structure Does DNA fit the requirements of a hereditary material?

41. Protein Synthesis DNA carries the instructions for the production of proteins.A protein is composed of smaller molecules called amino acids, and the structure and function of the protein is determined by the sequence of its amino acids. The sequence of amino acids, in turn, is determined by the sequence of nucleotide bases in the DNA. A sequence of three nucleotide bases, called a triplet, is the genetic code word, or codon, that specifies a particular amino acid.

42. Protein Synthesis Protein synthesis begins with the separation of a DNA molecule into two strands. In a process called transcription, a section of the sense strand acts as a template, or pattern, to produce a new strand called messenger RNA (RNA). The RNA leaves the cell nucleus and attaches to the ribosomes, specialized cellular structures that are the sites of protein synthesis. Amino acids are carried to the ribosomes by another type of RNA, called transfer (RNA). In a process called translation, the amino acids are linked together in a particular sequence, dictated by the RNA, to form a protein.

43. Replication Before replication, the parent DNA molecule has 2 complementary strands First the 2 strands separate Each “old” strand serves as a template to determine the order of the nucleotides in the new strand Nucleotides are connected to form the backbone; now have 2 identical DNA molecules.

44. Replication DNA Replication is simple, but it takes a large team of enzymes and proteins to carry out the process: • Helicase unwinds the molecule • Single-strand binding protein stabilized ssDNA • Primase initiates the replication with RNA • DNA polymerase extends the new DNA • Second DNA polymerase removes the RNA • DNA ligase joins all the fragments

45. 1971-Smith & Nathans Discovery of restriction endonucleases Hamilton Smith • Discovered HindII in Haemophilus influenzae Daniel Nathans • Used HindII to make first restriction map of SV40

46. 1972 - Paul Berg Produces first recombinant DNA using EcoRI 1973 -Boyer, Cohen & Chang Transform E. coli with Recombinant plasmid

47. 1977 - Genentech, Inc. • Company founded by Herbert Boyer and Robert Swanson in 1976 • Considered the advent of the Age of Biotechnology First human protein (somatostatin) produced from a transgenic bacterium. • Walter Gilbert and Allan Maxam devise a method for sequencing DNA.

48. 1978 • David Botstein discovers RFLP analysis 1980 • U.S. Supreme Court rules that life forms can be patented • Kary Mullis develops PCR. Sells patent for $300M in 1991

49. 1981 • First transgenic mice produced 1982 • The USFDA approves sale of genetically engineered human insulin 1983 • An automated DNA sequencer is developed • A screening test for Huntington’s disease is developed using restriction fragment length markers.

50. 1984 • Alec Jeffreys introduces technique for DNA fingerprinting to identify individuals 1985 • Genetically engineered plants resistant to insects, viruses, and bacteria are field tested for the first time • The NIH approves guidelines for performing experiments in gene therapy on humans