BIO325 - Lecture 3 - BIO325 22 January 2008 DNA Replication...

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BIO325 22 January 2008 DNA Replication (continued) I. Replication in E. Coli a. Origin of Replication i. Where the separation of the strands occurs b. DnaA box, DnaA i. Section on the origin ii. Binding site for protein DnaA iii. DnaA proteins also bind to each other to bend DNA around 1. Puts pressure on helix to push strands apart from each other 2. Changes helix to separate at adjacent sections c. AT-rich region i. A-T base pairs 1. Held together with two hydrogen bonds 2. G-C=3 ii. Smaller number of hydrogen bonds iii. Less energy to separate strands iv. Makes region easily separable v. Positioned exactly where DnaA protein has effect to force it apart vi. Constitutes, with DnaA box, the origin 1. Each alone is not enough to provide strand separation when needed to change shape and push strands apart d. Helicase i. Two copies ii. Come in to bind and start breaking more hydrogen bonds iii. Move away from each other to make replication bubble larger iv. Problem is that turns bunch up at either end during separation 1. Topoisomerase – helps with bunching of strands a. Breaks a phosphodiester bond in a strand of DNA b. Rotates helix around helix of the one backbone c. Reconnects phosphodiester bond that it broke
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BIO325 - Lecture 3 - BIO325 22 January 2008 DNA Replication...

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