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Introduction to Molecular Genetics

Introduction to Molecular Genetics. Rowan University Spring Semester Mrs. Patricia Sidelsky 2008. Regulatory RNAs. http://www.dnalc.org/ddnalc/dna_today/episodes/5/episode5.html. Molecular Genetics. Molecular genetics and molecular biology are almost synonomous terms A “ hybrid” science

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Introduction to Molecular Genetics

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  1. Introduction to Molecular Genetics Rowan University Spring Semester Mrs. Patricia Sidelsky 2008

  2. Regulatory RNAs

  3. http://www.dnalc.org/ddnalc/dna_today/episodes/5/episode5.htmlhttp://www.dnalc.org/ddnalc/dna_today/episodes/5/episode5.html

  4. Molecular Genetics • Molecular genetics and molecular biology are almost synonomous terms • A “ hybrid” science • The change in the understanding of life has led to a revolution in the field of Biology

  5. Molecular Genetics • The result of an amalgam of a variety of physical and biological sciences • Genetics, microbiology, biochemistry, physical chemistry, and physics • Driven by the need to understand the underlying principles of life and the reactions of life

  6. Max DelbruckIlustrates the blend in scientific disciplines • German immigrant • Originally trained in physical chemistry and theoretical physics • Converted to molecular genetics • Collaborated with Salvador Luria on the characterization and genetics of bacteriophages

  7. Molecular Genetics - Origins • Thomas Hunt Morgan- Columbia University • The physical nature of the gene • A discovery in 1910 changed the course of genetics • Developed experimental model for the study of modern genetics- the fruit fly – Drosophila melanogaster • The white eyed male mutant appeared in a culture of flies in the fly room and this was the beginning of a search for mutants

  8. White and Wild type

  9. Easy to cultivate • Prolific progeny • Small and inexpensive • Large polytene chromosomes • Diploid number 8 • Many mutations

  10. Hermann Joseph Muller • X rays cause mutations • Produced a variety of flies with phenotypes such asvestigial

  11. Alfred Sturdevant produced the first genetic map from linkage experiments • Genes were related to position on the chromosome map • Mutants were related to differences in the appearance of the polytene chromosomes due to staining

  12. DNA as Genetic MaterialTransformation • Griffith in 1928 observed the change of non-virulent organisms into virulent ones as a result of “transformation” • MacLeod and McCarty in 1944 showed that the transforming principle was DNA

  13. Figure 11.1

  14. Transforming principle

  15. Avery, McLeod, and McCarty

  16. Proof of the Transforming Principle • Chemical analysis of sample containing the transforming principle showed that the major component was a deoxyribose -containing nucleic acid • Physical measurements show that the sample contained a highly viscous substance having the properties of DNA • Incubatyion with trypsin or chymotrypsin, enzymes that catalzye protein hydrolysis or with ribonuclease( RNase), an enzyme that catalyzes RNA hydrolysis did not affect the transforming principle Incubation with DNase, an enzyme that catalyzes DNA hydrolysis inactivates the transforming principle

  17. Transfection

  18. DNA as Genetic Material( of viruses) • Hershey and Chase, 1952 • used bacteriophage T2 infection as model • DNA labeled with 32P;protein coat labeled with 35S • Only DNA entered cell but both new DNA and protein coats synthesized and incorporated into new viruses indicating that DNA had the genetic information for synthesis of both of these viral components

  19. T2 phage

  20. Chargaff’s Rule • Analyzed DNA from a variety of sources and improved both the separation and quantitation of the DNA bases • [C] = [G] and [A] = [T] • Today this is applied to the G=C or G.C pairs. Scientists describe the G+C content in organisms

  21. G+C • Now used as a means of classifying bacteria • G+C content varies in Gram Positive Bacteria • G+C content ranges from .27 in Clostridium to .76 for Sarcina • Most Eukaryotes have a value close to 50%

  22. G+C content • G+C content = [G] +[C] / all bases in DNA

  23. The Race for the Double Helix • Rosalind Franklin and Maurice Wilkins at Kings College • Studied the A and B forms of DNA • Rosalind’s famous x-ray crystallography picture of the B form held the secret, but she didn’t realize its significance

  24. Rosalind Franklin • Technically and scientifically a gifted scientist • Focused on the A form of DNA and missed the double helix

  25. The Race for the Double Helix • Watson and Crick formed an unlikely partnership • A 22 year old PhD and a thirty + PhD “want to be” embarked on a model making venture at Cambridge • Used the research of other scientists to determine the nature of the double helix

  26. Nucleic Acid CompositionDNA and RNA • DNA – Basic Molecules • Purines – adenine and guanine • Pyrmidines – cytosine and thymine • Sugar – Deoxyribose • Phosphate phosphate group http://www.dnai.org/index.htm -  DNA background

  27. Nucleotides • Sugar • Phosphate • Base • Adenine and guanine are purines • Thymine and Cytosine are pyrimidines

  28. Deoxyribose in DNA

  29. Double Helix • Two polynucleotide strands joined by phosphodiester bonds( backbone) • Complementarybase pairing in the center of the molecule A= T and C G – base pairing. Two hydrogen bonds between A and T and three hydrogen bonds between C and G. A purine is bonded to a complementary pyrimidine • Bases are attached to the 1’ C in the sugar by a glycosidic linkage • At opposite ends of the strand – one strand has the 3’hydroxyl, the other the 5’ hydroxyl of the sugar molecule

  30. DNA Structure http://www.johnkyrk.com/DNAanatomy.html - DNA structure

  31. Double helix( continued) • The double helix is right handed – the chains turn counter-clockwise. • As the strand turn around each other they form a major and minor groove. • The is a distance of .34nm between each base • The distance between two major grooves is 3.4nm or 10 bases • The diameter of the strand is 2nm

  32. Complementary Base Pairing • Adenine pairs with Thymine • Cytosine pairs with Guanine

  33. The end view of DNA • This view shows the double helix and the outer backbone with the bases in the center. • An AT base pair is highlighted in white

  34. Double helix and anti-parallel • DNA is a directional molecule • The complementary strands run in opposite directions • One strand runs 3’-5’ • The other strand runs 5’ to 3’ ( the end of the 5’ has the phosphates attached, while the 3’ end has a hydroxyl exposed)

  35. Prokaryote DNA • Tightly coiled • Coiling maintained by molecules similar to the coiling in eukaryotes • Circular ds molecule • Borrelia burgdoferi ( Lyme Disease )has a linear chromosome • Other bacteria have multiple chromosomes • Agrobacterium tumefaciens ( Produces Crown Gall disease in plants) has both circular and linear

  36. Prokaryote chromosomes Circular DNA

  37. Mitochondria • Mitochondrial DNA( mt DNA) • 16,500 base pairs • 37 genes • 24 encode RNA • Defects lead to diseases that are related to energy

  38. Chloroplast DNA • Chloroplast DNA( cp DNA) is larger than mitochondrial DNA • 195,000 bp • Genes for photosynthesis • Cp ribosomal RNAs

  39. Heavy and Light NMeselson and Stahl experiment

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