DNA

DNA is genetic material Chromosomes have DNA (4 nucleotides) and proteins (20 AA) Early hypothesis that genes are made of proteins Griffith’s experiment 2 strains of bacterium that underwent transformation: rough bacteria picked up smooth strain of DNA and became virulent Avery, MacLeod, and McCarty Experiment Lysed smooth (S) cells, separated contents into different types of macromolecules to see transformation ability (only DNA) Hershey-Chase Radioactively tagged protein coats and DNA of phages before affecting bacteria with virus (DNA/RNA and protein); conclusion that DNA = genetic info. Rosalind Franklin 3D structure, helical, 2 strands, consistent width helix, consistent distance between turns, nucleotides stacked like rungs of ladder Erwin Chargaff Purines (2 rings) AG = pyrimidines (1 ring) CT, A = T and C = G, A+T does not equal C+G A and T: 2 bonds, C and G: 3 bonds Watson and Crick DNA model explains how it carries genetic information/how info. Is replicated Double helix with 2 strands held together with H-bonds, sugar-phosphate backbone outside of helix joined by phosphodiester linkages, 4 nitrogenous bases (rungs) attached to backbone with covalent bonds A/T have 2 bonds, C/G have 3 bonds Antiparallel in opposite directions (3’ -> 5’ and 5’ -> 3’); complementary; each strand is template and mechanism for DNA replication 3’ end has free OH, 5’ end has free phosphate (for dehydration synthesis) Purine always pairs with pyrimidine (AT are straight ladders and CG are curved ladders) Nucleotide structure Phosphate, sugar (deoxyribose), nitrogenous base, pyrimidines (CT), purines (AG) DNA replication (check large organizer for transcription/translation) Semi-conservative replication, each new molecule of DNA has 1 parental strand and 1 newly synthesized strand Mutation: nucleotide sequence changes in DNA; permanent change in daughter molecule Evolutionary significance: if in germ cells, mutations can pass onto next generations (source of variation/new alleles)