Chapter 16Chromatin- made up of DNA and ProteinIdeas about genetic material circa 1940’s- The case for proteinso All the different variations- The case against nucleic acidso Only 5 nucleic acidso Structure is carbon rings with nitrogen baseso Purines and Pyrimidine o Deoxyribose sugar attached to DNAo Ribose sugar attached to RNAo Phosphate is also attached Building the Case for Nucleic Acids1928- Griffith recognized a principle (Process) - Proposes “Heritable substance transforms cells”- Transformation: change the genotype and phenotype due to assimiliation of external DNA- Pathogenic straino Living S (smooth) Straino Kills the mouse- Non Pathogenic Straino Living R (rough) cellso Mouse healthy- Heat-killed S cells (control)o Mouse healthy- Mixture of heat-killed S cells and living R cellso Mouse dieso Living S cells are in the mouse1944- Avery, McCarty, MacLeod experimentso Only DNA transforms cellso Living R + S-cell protein Mouse healthyo Living R + S-cell RNA Mouse Healthyo Living R + S-cell DNA Mouse DIES Only DNA transforms bacteria 1950- Erwin Chargraffo # adenines = # thymineso # guanines = # cytosinesBuilding the case for Nucleic Acids- Hershey and Chase -1952 (figure 16.4)o Viral DNA can program cells- Wilkins and Rosaline Franklin (X-ray crystallography) o X-ray diffraction: pass X-rays through aligned DNA fibers produces “shadows” of structure- Watson and Crick- 1953o Radically different structure 2 helical chains made of phosphate-sugars bases located on the insideo “Novel features”  paried bases: purine & pyramidine H-bonds hold together:- 2 between A/T, 3 between G/Co Other important points Ribose sugar would not fit Structure suggests replication mechanism o Components Phosphate Sugar-Deoxyribose Nitrogenous bases (ATGC)o Directionality: 5’ w/phosphate 3’ w/ -OH (on sugar) Antiparallel Orientation! Replication of DNASemi-conservative model of replications- proposed by Watson and Crick (1954)- Evidence provided by Meselson and Stahl (1958)- Experimental Setup (Fig 16.11):- Used heavy and light isotopes of nitrogen (15N and 14N) to label strands of DNA in separate rounds of replication. DNA Structure- Anti-Parallel Helix, sequence of bases- Covalent bonds, H-bonds When does DNA replication occur?- S phase of Cell Cycle DNA Replication: Initiation- Helicase- unwind and separate DNA- Single Strand binding protein – stabilize unwound DNA- Primase- synthesizes RNA primer from parental DNA: Synthesizing the new strand- DNA polymerase IIIo Requires template & primero ONLY synthesizes from 5’ to 3’o Incorporates one nucleotide at time, mathes parent nucleotide, forms covalent bond with 3’ end of previous sugar : Two methods of elongation1) Continuous synthesis on LEADING stranda. DNA Pol III Elongates2) Synthesize series of fragments on LAGGING StrandChromosomes get shorter after every replication.Telomeres allow limited cell divisions w/o eroding