Biology 1001A Lecture Notes - Semiconservative Replication, Polynucleotide, Pyrimidine
Document Summary
Purines: fused rings of c and n; adenine and guanine. Chargaff"s rules: number of pyrimidines = number of purines, # adenosine = # thymine; # cytosine = # guanine. Outcome of the classic messelson and stalh experiment. Used nonradioactive heavy 15n isotopes to tag potential dna (in order to be able to distinguish parent dna from newly synthesized ones) Used e. coli bacteria with an entire dna strand labelled with 15n. Discovered that new polynucleotide chains assembled on original chains as they unwind. Direction of movement of dna polymerase on the template strand. 5" end: exposed phosphate group attached to 5" c of sugar. 3" end: exposed hydroxyl group attached to 3" c of sugar. Dna strands run in antiparallel (opposite directions) Dna polymerase assembles chains in 5" > 3" direction ( reads template strand from 3" > 5") Semi-conservative: new polynucleotide chains assemble on original chains as they unwind.