Lecture 16

Lecture 16 - Lecture 16 DNA REPLICATION The regular pairing...

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Lecture 16 DNA REPLICATION The regular pairing of bases in the double-helical DNA structures suggested that new DNA strands are synthesized by using the existing parental strands as templates in the formation of new daughter strands, complimentary to the parental strands. Conservative Mechanism Semi-Conservative Mechanism -Two daughter strands form a new double-stranded DNA -Parental duplex remains intact MOTHER DNA KEPT INTACT -Parental strands permanently separated -Forms duplex molecule with daughter strands based paired to it DAUGHTER CELL: OLD + NEW STRAND Copying DNA template strand into complimentary strand is a common feature in: DNA replication, transcription of DNA into RNA and DNA repair and recombination. INFORMATION IN TEMPLATE IS ALWAYS PRESERVED IN SEQUENCE OF NUCLEOTIDES Meselston-Stahl Experiment Meselston-Stahl Experiment Goal : Prove that DNA replicates by a semi-conservative mechanism Procedur e 1. E.coli cells grown in a heavy medium prepared with heavy nitrogen ( 15 N) 2. Wash 15 N and grow cells in a non radioactive medium 14 N 1 | P a g e
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3. Separate the old (heavy) and new (light) DNA by centrifugation Result Conservative: Light and heavy species present at the end Semi-conservative : Single species (Light+heavy) but new d.s DNA present after 2 nd round -3 possibilities : Heavy, light and heavy+light H-H, L-L and H-L duplexes separated into distinct bands Conservative mechanism never generates H-L DNA Semi-conservative mechanism never generates H-H DNA Semi-conservative can generate H-L during second and subsequent doublings Density of signal : Measure of concentration Generation: Determined by counting the
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This note was uploaded on 06/05/2011 for the course BIO 200 taught by Professor Thomasebureau during the Fall '07 term at McGill.

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Lecture 16 - Lecture 16 DNA REPLICATION The regular pairing...

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