BIO 201 Lecture Notes - Lecture 32: Differential Centrifugation, Centrifugal Force, Dna Replication
6 Sep 2018
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Lecture 32: structure and replication of dna (ch. Dna must be copied for reproduction and growth (meiosis and mitosis) Discovered mechanisms of replication: label dna during replication with different isotopes of nitrogen, purify dna every generation. Identify density of dna at each generation using density gradient centrifugation: differential centrifugation, density gradient centrifugation. Particles whose mass is above a certain size pellet at selected centrifugal force. Particles settle where particle density matches solute density. Good for separation of structures with every different masses. Requires very high speeds and special equipment. Density gradient centrifugation of dna: extract dna, place in tube, centrifuge at 140,000g, observe dna with uv light. Meselson-stahl experiment: feed e. coli only 15n for many generations, replace 15n with 14n, take samples at multiple time points up to 4 generations, take samples and purity dna. 0. 3-0. 7 generations: some high and some intermediate density 15n:15n and 15n:14n. 1. 5 3. 0 generations: some intermediate and some low density 15n:15n and 14n:14n.
