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Eoin_Garcia_block5_MM10 (origin of replication (DNA replication begins at…
Eoin_Garcia_block5_MM10
DNA replication
Initiation
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Once DnaB attaches to the DNA, the initiation complex is complete and the DNA is ready for elongation.
Elongation
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In the 3’ direction, replication is continuous and carried out by a single DNA polymerase to produce the leading strand.
In the 5’ direction, several DNA polymerases work together to produce the lagging strand
Termination
Stalling is regulated by a protein called Tus, which recognizes and binds to 10 different terminator sites (ter sites) on the template DNA.
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origin of replication
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In bacteria, the origin of replication called oriC and includes 2 sets of consensus sequences called the 13-mer and 9-mer sequences.
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DNA polymerase
challenges
DNA pol III is unable to unwind the DNA double helix and denature the complementary template strands.
DNA pol III cannot initiate daughter strand elongation. It can only grow a DNA strand from preexisting RNA primers or DNA.
DNA pol III grows the new strands only in the 5’ to 3’ direction. As the strand denatures in the opposite direction, new strands need to be made in the 3’ to 5’ direction.
solutions
The unwinding of the double helix causes supercoiling. The enzyme gyrase stabilizes the uncoiled DNA to prevent supercoiling
The enzyme primase adds RNA primer to the parent template strand so that DNA Pol III can polymerize the complementary daughter strand in the 3’ direction.
DNA Pol I removes ribonucleotides of the RNA primer between adjacent Okazaki fragments on the lagging strand and fills the gap with deoxynucleotides. DNA ligase joins the adjacent fragments.
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