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Bi430/530 Theory of Recombinant DNA Techniques PowerPoint Presentation
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Bi430/530 Theory of Recombinant DNA Techniques

Bi430/530 Theory of Recombinant DNA Techniques

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Bi430/530 Theory of Recombinant DNA Techniques

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  1. Bi430/530 Theory of Recombinant DNA Techniques First part of course: Technical aspects of molecular biology work--Molecular Cloning Second part of course: Applications of molecular biology techniques Emerging science Bi530 student presentations Prerequisite: Molecular Biology (Bi 338) FRIDAY February 8: Midterm exam THURSDAY March 20: Final exam

  2. Syllabus

  3. Syllabus--first half The basics of DNA manipulation (and the Molecular Cloning Manual)

  4. “Molecular Cloning” (2001), Sambrook and Russel (3rd ed.) See also Course Reading #2 (detailed table of contents) in course packet

  5. Syllabus--second half Using DNA manipulation techniques

  6. Recombinant DNA

  7. Information flow in the cell DNA RNA protein

  8. Evolution: a dialog between the genome and its environment Replication/mutation DNA RNA protein Natural selection

  9. Organisms respond to their environment via information from sensory input and changes in gene expression DNA RNA protein environment Dynamic, immediate, transient modification of DNA program

  10. Species respond to environment over long time frames via mutations in the DNA program DNA RNA protein evolution environment --Stable (“permanent”) --reflects effect of environment over large time scales

  11. Human activity: transient modifications of environment, permanent modifications of DNA program DNA RNA protein Human intervention: genetics (indirect), rDNA (direct) environment

  12. 2006: 53 years of DNA structure Rosalind Franklin and Maurice Wilkins: X-Ray fiber diffraction pattern of pure B-form DNA (1953) James Watson and Francis Crick: Proposed two antiparallel, helical strands forming a stable duplex with DNA bases on interior of the molecule, joined by hydrogen bonds (1953) But DNA was not discovered in 1953--it had been known as the element of genetic transmission at least since 1947, when Avery showed that DNA could “transform” bacterial colony morphology Why was the structure so important?

  13. Structure of DNA To Watson and Crick, the structure suggested: --Mechanism for replication --Stability for information storage, yet accessing the information not difficult The DNA structure provided a new template for hypotheses regarding biological phenomena (amenability to study)

  14. DNA is easy to work with… • Readily isolated--plasmid isolation, PCR • Stable--not chemically reactive like RNA (even archaeologically stable!) • Easy to propagate and move from cell to cell • Easy to make specific constructs • Easy to make specific mutations • Very easy to sequence (record-keeping) • Predictable behavior • Sequence lends itself to analysis--genome projects

  15. DNA is very easy to sequence Etc….


  17. The behavior of DNA (genes) is predictable Gene sequence conservation often indicates functional similarity Non-protein coding information sequences can often be detected by homology (promoters for transcription initiation, transcription terminators, ribosome binding sites, DNA binding protein binding sites) the genetic code

  18. The genetic code and the roots of biotechnology 1961 Marshall Nirenberg and Heinrich J. Matthaei: polyU mRNA encodes poly-phenylalanine 1966 Nirenberg and colleagues had deciphered the 61 codons (and 3 nonsense codons) for all 20 amino acids 1968 Nobel prize for Nirenberg, Holley, and Khorana

  19. 1966 George and Muriel Beadle write: “The deciphering of the DNA code has revealed our possession of a language much older than hieroglyphics, a language as old as life itself, a language that is the most living language of all--even if its letters are invisible and its words are buried deep in the cells of our bodies.”

  20. The public reaction to the deciphering of the genetic code Wow “…just as big a breakthrough in biology as [Newton's discovery of gravitation in the seventeenth century] was in physics.” --John Pfeiffer, journalist, 1961 Optimism “No stronger proof of the universality of all life has been developed since Charles Darwin's 'The Origin of Species' demonstrated that all life is descended from one beginning. In the far future, the hope is that the hereditary lineup will be so well known that science may deal with the aberrations of DNA arrangements that produce cancer, aging, and other weaknesses of the flesh.” Chicago Sun-Times, 1962

  21. Caution …knowledge gained from the genetic code “might well lead in the foreseeable future to a means of directing mutations and changing genes at will.” 1961, A. G. Steinberg of Case Western Reserve University …knowledge of the genetic code could “lead to methods of tampering with life, of creating new diseases, of controlling minds, of influencing heredity, even perhaps in certain desired directions.”1961, Arne Wilhelm Kaurin Tiselius, 1948 Nobel Laureate in Chemistry

  22. 1967 “Will Society Be Prepared?” Marshall Nirenberg, editorial in Science (see WebCT)

  23. Nirenberg, 1967 "When man becomes capable of instructing his own cells, he must refrain from doing so until he has sufficient wisdom to use this knowledge for the benefit of mankind.... [D]ecisions concerning the application of this knowledge must ultimately be made by society, and only an informed society can make such decisions wisely."

  24. Response from Joshua Lederberg, 1967 (see letter on WebCT): (paraphrased) -- We need to be particularly careful with manipulation of the germ cell lines (heritable changes). -- Considerations governing control of our biology are equally important to considerations governing control of our cultural institutions (given that culture is mutable and heritable)

  25. 1975: The Asilomar Conference on Recombinant DNA • 1974: moratorium on recombinant DNA research • “…new technology created extraordinary novel avenues for genetics and could ultimately provide exceptional opportunities for medicine, agriculture and industry…. …concerns that unfettered pursuit of this research might engender unforeseen and damaging consequences for human health and the Earth's ecosystems”

  26. 1975: The Asilomar Conference on Recombinant DNA • Conference included internationally prominent scientists, government officials, doctors, lawyers, members of the press • Conclusion: “…recombinant DNA research should proceed but under strict guidelines.” • The moratorium was lifted, and “… guidelines were subsequently promulgated by the National Institutes of Health and by comparable bodies in other countries.”

  27. The Asilomar principles: • containment should be made an essential consideration in the experimental design • the effectiveness of the containment should match the estimated risk as closely as possible. Additional suggestions: Use biological barriers to limit the spread of recombinant DNA • fastidious bacterial hosts that are unable to survive in natural environments • nontransmissible and equally fastidious vectors (plasmids, bacteriophages, or other viruses) that are able to grow in only specified hosts

  28. The Asilomar principles: Safety factors • physical containment, exemplified by the use of hoods or where applicable, limited access or negative pressure laboratories • strict adherence to good microbiological practices, which would limit the escape of organisms from the experimental situation • education and training of all personnel involved in the experiments would be essential to effective containment measures.

  29. Regulation of biotechnology: US National Institutes of Health (NIH) Guidelines • stipulations of biosafety and containment measures for recombinant DNA research • delineations of critical ethical principles and safety reporting requirements for human gene transfer research • See • (see also CR #3 in course packet)

  30. “Unnatural Selection” (first reading in the course packet) By Allison Snow Is the process for altering genes (evolution vs. human): irrelevant? Product (transgenic organism): is the phenotype the only thing that is important? Reverberations from introduction of modified organisms? Spread of gene? Effects of spread? Success of organism? Effects on other organisms? “The technology’s main hazards are probably yet to manifest themselves”

  31. What can we do with recombinant DNA technology? • begin to learn how cells, tissues, organisms, communities work, interact, respond to the environment (gain scientific knowledge) • improve human health • industrial production of useful enzymes, metabolic products • improve industrial process • raise agricultural productivity • investigate problems of geneology, paternity, anthropology, archaeology • investigate criminal cases • etc….

  32. How is recombinant DNA technology useful in medicine? • Diagnosis of disease • Animal models for human diseases • Therapies • nucleic acids: gene therapy • pharmacologically active proteins • small molecule design and testing • Antimicrobials • Vaccines • Microbicides

  33. The biotechnology industry is very new Case in point: Genentech (S. San Francisco) 2006: Genentech to open production facility in Portland (2010)

  34. Day 1 summary: The simplicity of a DNA-based information system makes genetic manipulation possible This represents an unprecedented level of interaction with living systems Benefits and costs of technology require continuous assessment

  35. Visualizing DNA (and RNA, protein): non-specific detection methods • Quantitation of DNA (Course Reading 4) • Electrophoresis (Course Reading 5 ) • Visualizing DNA (& protein) in gels (Course Reading 6)

  36. Quantitation of DNA by UV absorbance • Measure absorbance of UV light by sample (the aromatic bases have a characteristic absorbance maximum at around 260 nanometers) • 1.0 A260 (1 cm light path) = DNA concentration of 50 micrograms per ml (double stranded DNA) or 38 micrograms per ml (single-stranded DNA or RNA) • the effective range for accurate measurement is rather narrow: A260 from 0.05 to 2.0 (DNA concentrations from 2.5 to 100 micrograms/ml) • Sample must be very pure for accurate measurements (RNA, EDTA and phenol all absorb at 260 nm)

  37. How can concentration be determined by absorbance? DNA has a characteristic “molar extinction coefficient”  The Beer-Lambert law: I = Io10- dc I = intensity of transmitted light Io = intensity of incident light  = molar extinction coefficient d = optical path length c = concentration of absorbing material How much light gets through a solution depends on what’s in it and how much of it there is

  38. The Beer-Lambert law: • I = Io10- dc • Absorbance A measured by a spec is log I/Io • When path length d = 1 cm, A is called the optical density OD • If you know the , the absorbance of a solution will tell you the concentration: • OD = c • for nucleic acids: dsDNA: 6.6 ssDNA, RNA: 7.4 (but these values change with pH and salt concentration!)

  39. A typical (good) “scan” (multiple wavelengths) of a DNA sample A260/A280: 1.8 is good (lower values indicate significant protein contamination) 0.5 A260 = 0.327 Absorbance (1 cm path length) 0 200 260 400 Wavelength (nm)

  40. How does A260 give you the quantity of DNA? Example: sample of 250 base pair fragment of DNA has an A260 = .327 What is its molar concentration? Given: (1.0 A = 50 micrograms/ml DNA) DNA conc. = .327 x 50 = 16.35 micrograms/ml MW of an average bp. = 650 Daltons Therefore 250 bp. Fragment has a MW of 1.6 x 10 5 Daltons Solve for molarity: 1.02 x 10 -7 M, or 102 nanomolar (nM) Important to know how to do this calculation

  41. What is the molarity of a 16.35 microgram/ml solution of a 250 base pair DNA fragment? 1 gram 1 mole 1000 ml 16.35 micrograms 1 ml 106 micrograms 1 L 1.6 x 105 grams 1.02 x 10 -7 molar 0.102 x 10-6 molar [0.1 micromolar (M)] 102 x 10-9 molar [102 nanomolar (nM)]

  42. Fluorometry: another method for quantitation of DNA • Hoechst 33258 (a fluorescent dye) • Binds to DNA in the minor groove (without intercalation) • Fluorescence increases following binding • Good for quantitation of low concentrations of DNA (10-250 ng/ml) • rRNA and protein do not interfere • But you need a fluorometer

  43. Another method for quantitation of DNA: • Ethidium bromide (fluorescent dye) binding • Compare sample DNA fluorescence to standards of known concentration (dilution series) • In solution *or* using gel electrophoresis A commercially available quantitative DNA standard

  44. Visualizing DNA: Electrophoresis • Allows separation of biomolecules (DNA, RNA, protein) on basis of size • A separation matrix, or gel (agarose or polyacrylamide), is saturated with an electrically conductive buffer • Samples are loaded, an electric field is applied, and negatively charged biomolecules in the sample travel toward the cathode • The larger the molecule, the slower the travel through the gel matrix • Dyes allow a visual estimate of the rate of travel through the gel • The choice of matrix depends mainly on the size of DNA being analyzed

  45. Agarose gels Agarose: a polysaccharide polymer of alternating D- and L-galactose monomers, isolated from seaweed • Pore size is defined by the agarose concentration (higher concentration, slower DNA migration overall) • The conformation of the DNA (supercoiled, nicked circles, linear) affects the mobility of the DNA in gels • Rate of DNA migration is affected by voltage (5 to 8 Volts/cm is close to optimal) • Agarose comes in a myriad of types (variable melting temperatures, generated by differential hydroxyethylation of the agarose)

  46. Agarose gels Standard gels can separate DNA fragments from 100 bp to about 20,000 bp Pulsed-field gels separate very large DNA fragments (up to 10,000,000 bp, or 10 Mb) This apparatus allows periodic shifts in the direction of DNA migration: 120° refers to the reorientation angle (difference between orientation of electric fields A and B

  47. Typical agarose gel Load samples in wells xylene cyanol bromophenol blue - +  (the DNA fragments are not visible without some sort of staining) time of electrophoresis (progress monitored by marker dyes)