BIOLOGY 111 1st Edition Lecture 19 Outline of Last Lecture I. Parental Type OffspringII. Recombinant Type OffspringIII. Frequency of RecombinationIV. Linkage MapV. Alteration of ChromosomeVI. EpigeneticsOutline of Current Lecture I. Molecular Basis of Inheritance II. Chargaff’s RuleIII. DNAIV. Base Pairing V. Replication of E. coliVI. Replication ProblemsVII. DNA packaging Current LectureMolecular Basis of Inheritance - Frederick Griffith's bacterial transformation in 1920'so experiment: studied the bacteria of S (smooth)-pathogenic and R(rough)-control (non-pathogenic) to test for the trait of pathogenicity- Avery, MacLeod, and McCarthy (1944) used purification methods to reveal that DNA is genetic material - Alfred Hershey and Martha Chase (1952) DNA is the genetic material o viruses infecting a bacterial cell  phages (bacteriophages) called T2 attach to the host cell and inject their genetic material through the plasma membrane while the head and tail parts remain on the outer bacterial surface- Purines (Adenine and Guanine)- Pyrimidines (Thymine and Cytosine) - Chargaffs Ruleo the base composition varies between species o within the species, the number of A and T bases are equal and the number of G and C bases are equal These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- James Watson and Francis Crick, with Maurice Wilkins (1953) constructedthe DNA modelo DNA is double stranded, helix-shaped, sugar phosphate backbone and paired bases on the inside o A pairs with To G pairs with C o keeps a consistent width (they have to pair purine to pyrimidine because if two purines pair, the diameter would be too wide, and if two pyrimidines pair it would be too narrow)o 2 DNA strands are complementary (DNA goes from 5' end to 3' end) 5'- GCGGATTT -3' 3'- CGCCTAAA -5'- Base Pairing of DNA o the pairs of nitrogenous bases in DNA are held together by hydrogen bonds o A and T are held together by two Hydrogen bondso G and C are held together by three Hydrogen bondso in addition to hydrogen bonding, there is also van Derr Walls Interaction that adds to the stability of DNA - Replication of E. coli o begins at origin at replication where a replication bubble is formedo at each end of the replication bubble is a replication fork (creating a Y-shape)o Helicase untwists the double helix at the replication fork and separates the two strands o single strand binding proteins protect the unwound strands from repairing while being copiedo Topoisomerase works ahead of the replication fork to swivel to DNA strands, relieving strain so that helicase can unwind with no problems o the unwound sections of parental DNA strands are now used as templates for synthesis of complementary DNA strandso Nucleotides ALWAYS added to the 3' end of each strando synthesization of a new DNA strand by DNA polymerase which adds nucleotides to a preexisting chain- DNA polymerase 3 - synthesizes the leading strand and also has proof-reading capabilities (back-up and fixes its mistakes) o nucleotide excision repair - mismatched nucleotides escaped proof-reading or if they are damaged after replication, the damage iscorrected at this pointo Dimer - damage - DNA polymerase 1 - removes RNA primers and and replaces with DNAo Antiparallel elongation leading strand - made by DNA polymerase 3, continuous elongation in the 5' to 3' (toward) direction as the replication fork progresses lagging strand - moves away from the replication fork  Okazaki fragments - segments of the lagging strand- Replication of eukaryotes o requires several replication bubbles and serveral replication forks- Replication problemo chromosomes would become even shorter, except for telomeraseadds short stretches of nucleotides (telomeres) to the ends of each chromosome o telomeres are repeats of 6 nucleotides 100-1000 times  they do not contain genes  they carry their own template so it can extend DNA without having to copy information from the other strand - Packaging of DNAo Histone Octamers (8 histones that come together) make nucleosomes o sizes in diameter as DNA is packaged  2nm DNA 10nm nucleosome 30nm fiber 300nm fiber (composed of the 30nm fibers looped and folded up) 700nm chromatid 1400nm replicated chromosome - Euchromatin is dispersed and can be expressed- Heterochromatin is highly condensed and cannot be expressed (until it isconverted to euchromatin by modifying its