Notes Feb 17 - Notes Feb 17 Table 25.2 - DNA polymerase...

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Notes Feb 17 Table 25.2 - DNA polymerase alpha o Extends 5’-3’ direction o Doesn’t have proofread exonuclease o Moderately processive o Important role is that it associates with primase (which is a RNA polymerase) o In the case of eukaryote, there is a protein complex consisting of pol alpha and a different protein subunit that is the primase that travel together on the DNA laying down a few primers either at the origin or at the lagging strand okazaki fragments o Pol alpha extends the primer with DNA a little bit with only around 15 nucleotides that get erased and that’s why it doesnt matter if there is a certain error frequency o Role of DNA pol alpha is just to get things started at the origin or at the okazaki fragment - Pol delta and epsilon divide the replication and polymerization work - It is now thought that epsilon is on the leading strand and delta is on the lagging strand - PCNA- eukayote sliding clamp o Binds to DNA pol delta and epsilon Fig 25.21 - Beginning of an okazaki fragment - Green is RNA primer - A little bit of DNA is synthesized by pol alpha extending the primer for a bit (blue extension) - Regular DNA pol (delta or epsilon) extends that RNA primer - Why does DNA polymerase alpha not need a 5’ to 3’ proofreading exonuclease? o If there are errors, RNAase H removes the RNA primer leaving 1 ribonucleotide, then some other nuclease chews that, and the part that was made by DNA pol alpha, especially if there is an error, so 1 in 10^ time there will be an error in DNA pol alpha; but the DNA coming from the other lagging fragment fills in the gap and that one is done by a pol that does have a proofreading exonuclease o Eukatyotes have this odd feature where a DNA pol alpha is used to extend primers, and while there might be a relatively high error rate, flap endonuclease will chew away the error, and then you get extension by a normal DNA pol with high processivity - Removal of RNA primers in Eukaryotes
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o RNAase H1 excises all bu tthe 5’ ribonucleotide of the RNA primer o FEN1, a 5- 3’ endonuclease then removes the remaining ribonucleotide along
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This note was uploaded on 09/14/2011 for the course BIO 362 taught by Professor Walikarzai during the Spring '10 term at SUNY Stony Brook.

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Notes Feb 17 - Notes Feb 17 Table 25.2 - DNA polymerase...

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