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Transcript
DNA REPLICATION HOW IS DNA DUPLICATED IN THE SYNTHESIS STAGE? DISCOVERY OF THE GENETIC MATERIAL • Griffith – studied the bacteria that causes pneumonia in mice; this disease-causing factor could be passed between two strains of bacteria • Avery – using the same type of cells as Griffith, broke the strains down to the component macromolecules to determine nucleic acids (DNA) were responsible for the transformation • Hershey and Chase – confirmed DNA was the transforming factor by using radioactive labeling in viruses DNA STRUCTURE • Levene – basic structure of nucleotides • Five carbon sugar, phosphate group, and nitrogenous base • Many nucleotides compose a nucleic acid (DNA or RNA) • Sugars • DNA – deoxyribose (one less oxygen) • RNA – ribose • Nitrogenous Bases • Guanine (G) and adenine (A) – double rings (purine) • Thymine (T) and cytosine (C) – single rings (pyrimidine) CHARGAFF’S RULE • Amount of A = T and amount of C = G which means… • Chromosome consists of 51-245 million base pairs • Only 5 centimeters long...how does it fit? • Tightly coils around histones • DNA + histone = nucleosome WILKINS, FRANKLIN, WATSON, AND CRICK • Photo 51 via x-ray diffraction • Double helix/twisted ladder • Controversies in science • DNA Structure • Two outside strands containing an alternating phosphate and sugar • Cytosine and Guanine paired together by three hydrogen bonds • Thymine and adenine paired together by two hydrogen bonds SO THAT’S THE STRUCTURE, HOW IS IT REPLICATED? • Semiconservative replication – one strand serves as a template (Watson and Crick) THE PROCESS • Unwinding – DNA Helicase • Replication fork • Hydrogen bonds are broken • RNA Primase follows behind to add an RNA primer • Orientation – 3’ and 5’ ends THE PROCESS (CONT.) • DNA Polymerase adds the appropriately paired nucleotides to the template DNA strand • The template strand is read from the 3’ to the 5’ end • The new strand is created in the 5’ to the 3’ orientation antiparallel to the original one New Old LEADING AND LAGGING STRANDS • Because the template strand is always read from the 3’ to the 5’ end, it is “easier” for DNA polymerase to replicate one of the template strands (leading strand). • Okazaki Fragments result in the lagging strand CONCLUSION • DNA replication occurs in many places on the chromosome at once • Another DNA polymerase comes through and replaces the RNA Primers with nucleotides • DNA Ligase links the many fragments of DNA • Including the Okazaki fragments • Prokaryotic replication – one origin of replication (DNA is called a plasmid) • Transformation – bacteria extracts DNA from an outside source