Scientist Experiment/Discovery Watson and Crick 1953: Discovered DNA double helix, said at end of paper that structure suggests possible mechanism. Matthey Meselson and Franklin Stahl 1958: Proved that semi-conservative model was correct copying mechanism: Cesium chloride equilibrium-density gradient centrifugation. Cesium goes to bott stops where density of cesium is equal to density of DNA strand. Bidirectional replication from multiple origins for eukaryotic replication. Pulse labelling with radioactive thymine. Pulse label with 3H-Thumidine, then put in non medium, see multiple origins and tails with decreasing grain density. Francis Crick 1958 – Central Dogma Postulated tRNAs before they were seen Predicted several tRNAs must recognize more than one codon – Crick’s wobble hypothe Berget and Chow (separate) 1977 – process mRNA, hybridize with DNA, mix with denatured gene (single stranded), base pairing to template strand, intron regions do not bind and therefore form loop. Thomas Cech 1989 Nobel prize for discovery of catalytic RNAs Robert Holley 1968 Nobel Prize for nucleotide sequence of a yeast tRNA Marshall Nirenbirg and Ghobind Khorana 1968 Nobel Prize – Deciphering genetic code Prepared bacterial extract with components required except mRNA to make protein Add mRNA with only one base, polypeptide has single amino acids. (Amino acyl tRNA triple codons). Ditto with mixed polynucleotide. Ribosomes activated with a trinucleotide mini-mRNA in the presence of 14C-Phe and 14 phenylalanyl-tRNA Phe forms complex/ Barbara McClintock Discovered transposable elements in 1940s (Nobel prize) Breakage-Fusion-Bridge (1936-1941) – was studying chromosome breakage in corn. Bre chromosome into new cells – duplication, ends fuse (telomeres fuse because of damage a complex comes apart, etc), bridge (attempt to separate), breaks in wrong place, changes i amplifications and deletions of genes. Also discovered that breakage caused clear kernels to become mosaics with bown-purple analysis of mechanism of chromosome breakage showed Ds and Ac transposable elemen
Left behind wisdom that DNA was static – was not accepted (called them “jumping gene in 1983. Colleague made mutant that couldn’t made antibody – caused by transposons inserting in Thomas Hunt Morgan Studied mutagenic effects of transposons in Drosophila. Francois Jacob and Jaques Monod Proposed operon model in 1961 to explain regulation of genes for lactose utilization in E in 1965 DNA REPLICATION PROKARYOTIC DNA REPLICATION Right handed DNA (B-DNA) is most common in living cells 0.34nm between stacked bases, 10bp/turn, 3.4nm/helical turn For replication – takes place at oriC: Four (9 mer) DnaA (initiation protein) binding sites. DnaA binds to them, more molecules of DnaA bind cooperatively, make protein with oriC wrapped on the surface. This bends the strand, facilitating opening of adjacent 13- mer sequence. AT rich region that undergoes strand separation (13-mer). DnaB (helicase – on 5’ strand) and DnaC (helicase loader) join initiation complex and make replication bubble.
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