School of Biosciences and Veterinary Medicine University of Camerino

Transcription

1 School of Biosciences and Veterinary Medicine University of Camerino MOLECULAR BIOLOGY, GENERAL GENETICS Molecular Biology Course Attilio Fabbretti, PhD

2 What is molecular biology? SCIENTIFIC METHOD OBSERVATIONAL BIOLOGY MOLECULAR BIOLOGY PREDICTIVE/EXPERIMENTAL BIOLOGY

3 C. Darwin 1859 G. Mendel 1866 F. Miescher 1869 A. Kossel 1881 W. Sutton 1902 Timeline P.A. Levene 1920 F. Griffith 1928 O.T. Avery 1944 E. Chargaff 1951 A.D. Harsey 1952 R. Franklin 1952 J. Watson 1953

4 Charles Darwin Alfred Wallace: patterns in the geographical distribution of living and fossil species could be explained if every new species always came into existence near an already existing, closely related species On the Origin of Species, published on November 1859 Evolutionary theory: all species of organisms arise and develop through the natural selection of small, inherited variations that increase the individual's ability to compete, survive, and reproduce.

5 Gregor Mendel 1866 Fundamental laws of inheritance. He deduced that genes come in pairs and are inherited as distinct units, one from each parent

6 Felix Hoppe-Seyler laboratory at the Faculty of Natural Science in Tubingen Friedrich Miescher was given the task of researching the composition of white blood cells.

7 Friedrich Miescher in 1869 isolated a substance from the pus of open wounds collected from bandages in a nearby clinic.

8 Miescher protocol: Collect used bandages from clinic daily Separate cells via soaking in (9:1 water : sodium sulfate) solution Found 5 protein-like entities (via solubility properties). Also found other substance, unlike any known protein Tried to stain new nucleus material with iodine, which causes proteins to turn yellow

9 Conclusion: Mysterious substance is not protein New material from nuclei had unexpected properties: precipitated by acidifying solution and re-dissolved by making solution more alkaline ( basic )

10 Further study implied need for increased purity of mysterious substance Developed complicated protocols involving, e.g., warm alcohol; acid in pig s stomach, which contained enzyme pepsin; ether

11 He determined that nuclein was made up of carbon, hydrogen, oxygen, nitrogen and an unexpected element: phosphorus. He was the first to identify as a distinct molecule.

12 Albrecht Kossel, Emeritus Professor of Physiology in the University of Heidelberg, identified as a nucleic acid in 1881 and provided its present chemical name.

13 In one of his first experiments he boiled nuclein in water to release the phosphorus, and then refined these experiments to show that "among the soluble cleavage products of the nuclein whose examination has not yet been completed, one can demonstrate the presence of hypoxanthine, which is not insignificant".

14 In 1893 he was the first to recognize that nucleic acids also contained a carbohydrate. He reported the presence of a reducing sugar in yeast nuclein which he described as a pentose (i.e. with 5 carbon atoms in its structure). In 1910 The first Nobel Prize (Physiology or Medicine) for research on Deoxyribonucleic Acid

15 Phoebus Levene chemist Levene made important contributions to understanding Miescher s nuclein, now universally called deoxyribonucleic acid () Miescher determined relative amounts of five elements in, but not chemical structure.

16 .with more modern chemistry techniques Levene characterized chemical structure of ; contained four bases: adenine, guanine, thymine, cytosine, as well as deoxyribose, and phosphate group

17 In addition to determining chemical constituents of, Levene also concluded that the basic unit was composed of a base attached to a sugar and that the phosphate also attached to the sugar (first definition of nucleotide: phosphate-sugar-base). He also figured out the sugar difference between and RNA. uses deoxyribose sugar in its backbone; RNA uses ribose sugar.

18 He (unfortunately) also erroneously concluded that the proportions of bases were equal, and that there was a tetranucleotide that was the repeating structure of the molecule. Tetranucleotide Led to conclusion: could not carry genetic information. Thus, biologists thought protein was basis of heredity

19 Frederick Griffith 1928 New progress started from unlikely source: Medical officer of British Ministry of Health, Frederick Griffith His specialty: Pneumonia His concern: Significance in spread of disease of different pneumococcal types

20 Griffith studied varieties of different types pneumonia; examined for his 1928 report on 278 cases. Also conducted large number of experiments on mice of various strains of pneumococcal types under wide variety of conditions and pre-treatments of various strains of pneumococci

21 Some colonies of pneumococci had rough surfaces ( R form, small); these pneumococci were generally not virulent Some colonies had smooth surfaces ( S form, large) and were virulent. S colonies are larger because of the gelatinous capsule on the S cells they are VIRULENT!

22 Big surprise: R forms convertible to S forms when mixed with killed (via heating) S forms. What was Transforming Principle?

23 Griffith s results were subject of comment and inference, but little or no new experimentation, mostly near repetition. Oswald Theodore Avery, MacLeod, and McCarty in They decided to seek and to study chemical nature of substance(s) inducing transformation (=conversion) of pneumococcal types

24 How did Avery et al. proceed? Approach: Isolate, purify, and test chemical agent responsible for transformation in vitro, to better control Procedure: S form of bacteria treated essentially following Miescher protocol.

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27 Detailed chemical basis for actions of in this study were wholly unknown. But this 1944 paper through its careful experimental basis and detailed discussion considered landmark in biology: it seemed to establish with little doubt relevance of, as opposed to proteins, to secret of heredity.

28 Erwin Chargaff in Analisys of composition by paper chromatography

29 Sourc e mol % of bases Ratios A G C T A/T G/C %GC PhiX Maize * Octopu s A/T 1 G/C 1 [Chargaff Rule] Chicke n Rat Huma n is not a simple repeating polymer! P.A. Levene assumption was wrong

30 Alfred Hershey and Martha Chase in What is responsible for heredity protein or? Use radioactive tracers, 32 P () and 35 S (protein), in virus (= wrapped in protein) that infects bacteria no phosphorus in protein; no sulfur in. Therefore, means to distinguish two possibilities

31 The history of the discovery of The Phage Club : M. Delbruck, S. Luria, A. Hershey The phage group started around 1940 and was an informal network of biologists centered on Max Delbrück that contributed heavily to bacterial genetics and the origins of molecular biology in the mid-20th century. The phage group takes its name from bacteriophages, the bacteria-infecting viruses that the group used as experimental model organisms.

32 from T2, not the protein, is the genetic material!

33 Free download

34 All started with X-Rays Maltese cross

35 1953 Maurice Wilkins and Rosalind Franklin (both radiologists) X-ray data that showed the repeating units of

36 You already know the end of this story Watson and Crick determined the double helix arrangement of (Cambridge, England) The double helix model was intorduced to the world in the magazine Nature in 1953.

37 Microbiology and Cell biology Timeline

38 Welcome into MOLECULAR BIOLOGY!!!