Transcript E. coli
Introduction to Molecular Biology Fundamental Molecular Biology Historical Background Classical Experiments Structure of nucleotides & DNA What is Molecular Biology? Study of biological events at a molecular level The study of genes and gene activity at the molecular level DNA History Discovered in 1869 by Friedrich Miescher as a component of nuclein By late 19th C. DNA & RNA are known to be polymers The function of these nucleic acids was not known Early 20th C. Mendel’s genetics were rediscovered The concept of a ‘gene’ entered biology The question was “What makes up genes?” Three possibilities: DNA, RNA, or Proteins Three sets of researchers provided the data that once and for all settled the question 1928: Fredrick Griffith experimented on transformation 1944: Oswald Avery, Colin MacLeod, & Maclyn McCarty repeated Griffith’s experiments, but added further biochemical tests 1952: A.D. Hershey & Martha Chase performed their experiment with bacteriophage Griffith’s Transformation Experiment Avery et al. repeated the experiment, but looked at each class of molecules to see their potential to transform Hershey – Chase Experiment Erwin Chargaff’s Data Allison, Fundamental Molecular Biology Chargaff’s Rules How is information encoded within DNA Erwin Chargaff found that: [purine] = [pyrimidine] [Adenine] = [Thymidine] [Cytosine] = [Guanine] DNA Structure DNA X-Ray Diffraction Pattern Created By Rosiland Franklin Karp, Cell& Molecular Biology, 3E Watson & Crick Model of DNA Double Helix http://salmon.psy.plym.ac.uk/year3/PSY339EvolutionaryPsychologyroots/watson-crick-dna.jpg How does a helix of uniform pattern store information? Nucleotide Structure Sugars Nitrogenous Bases Phosphates Glycosidic Bond Base + Sugar = NUCLEOSIDE Base + Sugar + Phosphate = NUCLEOTIDE Essential Cell Biology, 2/e Phosphodiester Linkage Allison, Fundamental Molecular Biology DNA Structure Watson-Crick Model of DNA Two chains of nucleotides form a right-handed helix Chains run in opposite directions Sugar-phosphate backbone is on the outside of the chains The paired bases are in planes nearly perpendicular to the long axis of the molecule (Base Stacking) Hydrophobic interactions/Van Der Waal forces stabilize The two strands are held together by hydrogen bonds 1.09 nm 0.34 nm 0.27 nm 0.6 nm 0.34 nm Allison, Fundamental Molecular Biology Allison, Fundamental Molecular Biology 2.0 nm 3.4 nm 0.34 nm -6° Tilt 34.3° Twist http://www.web.virginia.edu/Heidi/chapter12/chp12.htm 3 Forms of DNA 2.4nm per turn 3.4nm per turn 11bp per turn 10.5bp per turn 4.6nm per turn 12bp per turn http://members.tripod.com/arnold_dion/RecDNA/Fig1-2.gif http://chemistry.umeche.maine.edu/CHY431/Nucleic5.html If the DNA is wound so that there are fewer bases per turn <9 bp, it is overwound creating positive supercoiling The angle of twist increases from 34.3° to 37.7° If there are more bases per turn >11 bp, it is underwound creating negative supercoiling The angle of twist decreases from 34.3° to 30.9° 30.9°< >37.7° 34.3° Essential Cell Biology, 2/e E. coli genome negatively supercoiled http://www.cbs.dtu.dk/staff/dave/roanoke/genetics980213a.html 11.1Å 10.8Å Allison, Fundamental Molecular Biology