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2012.02.15 - Bio 1202 Lecture Review Notes.docx

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Western University
Biology 1202B
Gardiner/ Murphy

Biology Lecture Review Notes Lecture 2 DNA Replication  Semi-conservative: o The double helix opens, and new strands synthesize to create 2 strands o The only type that appears to be biologically significant  Conservative: o The one double helix is completely intact, and the new double helix is completely from new nucleotides  Dispersive: o Mixture of both new and old strands  1958 – Meselson and Stahl – grew bacteria for several generations in N (heavy) medium and 14 then transferred them to N (normal/light) medium and allowed them to grow and divide for several generations o All DNA is heavy before the transfer (in a test tube they were at the bottom) o All DNA is light after the transfer o DNA was extracted from the bacteria cultured in the N medium and after each 14 generation in the N medium o The DNA was centrifuged at a high speed for 48 hours o Grew them in nitrogen because it is an important part of DNA o The results completely matched with semiconservative replication  Did not support conservative or dispersive  DNA synthesis occurs in 5’ to 3’ direction!  Alpha, beta, and gamma (phosphate groups): o Alpha is the one that stays o Beta and gamma are the ones that are removed (the pyrophosphates)  Eukaryotes are slower at replicating DNA because they are more complex  Replication fork – where the antiparallel DNA strands replicate  Leading strand – can start replication at the first nucleotide o Continuously made  Lagging strand – has to open up to begin replication (is not able to replicate on the first nucleotide because of the 5’ to 3’ direction) o Discontinuously made (Okazaki Fragments)  Helicase – a protein that unwinds the DNA helix  There are single stranded binding proteins that bind to DNA and stabilize its single stranded form  Primase – makes the primers (RNA primers) that are used to synthesize the DNA o Synthesizes and assembles short complement
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