CHAPTER 16 Molecular Basis of Inheritance First experiment Federick Griffith s bacterial transformation in 1920s o Transformation change in genotype and phenotype due to assimilation of external DNA o Some factor from dead smooth cells transformed rough cells into smooth virulent ones Avery MacLeod and McCarty 1944 used purification methods to reveal that DNA is the genetic material o Only purified DNA from type S could transform type R not the protein or the RNA o Purified DNA might still contain traces of contamination that may be the transforming principal Alfred Hershey and Martha Chase 52 o DNA is the genetic material o T2 virus affecting E coli Bacteriophage Chemical structure of DNA phosphate backbone o Polymer of nucleotides containing one of 4 nitrogenous bases deoxyribose sugar and o Purines A G o Pyrimidines T C o Hydrogen bonds btwn nitrogenous bases o A T C G o X pattern suggested that DNA contains structures with dimensions of 2nm 34nm and 3 4nm o Dark strucutres indicated that DNA contains repeating units o Rosalind Franklin s X ray diffraction results suggested A HELICAL STRUCTURE WITH Erwin cHargoff analyzed base composition of DNA of many different species UNIFORM DIAMETER o Results consistently showed The base composition of DNA varies between species In any species the number of A and T bases are equal and the number of C and G bases are equal Humans 30 3 A T 19 5 G 19 9 C James Watson and Francis Crick o Constructed model of DNA o Watson crick and wilkins awarded nobel prize in 62 o Used Linus paulings method of working out protein structures using simple ball and stick models o DNA IS DOUBLE STRANDED HELICAL o Dna strands are antiparallel and complimentary 5 3 and 3 5 o Phosphodiester bonds hold PHOSPHATE AND SUGAR TOGETHER IT IS COVALENT o A T has 2 hydrogen bonds C G has 3 hydrogen bonds Van der walls interactions btwn closely stacked nucleotides contribute to stability of dna 10 base pairs per turn of helix Nucleotides are 34nm apart Your genome has 3 billion base pairs DNA is approx 2 meters nucleus is 10 m 1958 Matthew Meselson and Franklin Stahl o Semiconservative model of DNA replication WORKS DNA replication o Copying of DNA is remarkable fast in its speed and accuracy o More than a dozen enzymes and other proteins participate in DNA replication PROKARYOTE EUKARYOTE o Circular dna o Replication bubble crates Replication fork o Several origins of replication several bubbles o Helicase unzips o Topoisomerase relieves additional coiling o Primase makes RNA primer o Single strand binding proteins stabilizes ssDNA and keep strands open o DNA polymerase able to covalently link nucleotides together from a primer can only link nucleotides in the 5 3 direction
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