11- DNA Replication - Chapter 11: DNA Replication I....

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Chapter 11: DNA Replication I. Structural Overview of DNA Replication a. Existing DNA Strands Act as Templates for the Synthesis of New Strands i. The two complementary strands of DNA come apart and serve as template strands for the synthesis of two new strands of DNA ii. To complete replication a covalent bond is formed between the phosphate on one nucleotide and the sugar on the previous nucleotide, the two newly made strands are the daughter strands while the original are template strands or parental strands II. Bacterial DNA Replication a. Bacterial Chromosomes Contain a Single Origin of Replication i. Origin of replication: site where DNA synthesis begins 1. bacterial chromosomes have a single origin of replication and proceeds bidirectionally (in both directions) 2. SO, two replication forks move in opposite directions out from the origin and they eventually meet each other on the opposite side of the bacterial chromosome to complete it b. Replication Is Initiated by the Binding of DnaA Protein to the Origin of Replication i. The origin for E. coli is named oriC for origin of Chromosomal replication ii. oriC has three functionally important DNA sequences 1. AT-rich region 2. DnaA box sequences 3. CATC methylation sites iii. Replication is initiated by binding of DnaA proteins to sequences within the origin known as DnaA box sequences 1. this stimulates cooperative binding of additional proteins to form a large complex 2. additional DNA binding proteins like HU and IHF causes the DNA to bend around the complex of DnaA proteins and separates the strand at the AT-rich region iv. after Denaturation of AT-rich region, DnaA proteins with the help of DnaC protein, recruit DNA helicase enzymes (aka DnaB helicase) to bind to this site v. two DNA helicases separate the strands 1. they use energy from ATP hydrolysis to catalyze the separation 2. they bind to single stranded DNA and travel along in 5’ to 3’ direction 3. when a helicase encounters a double stranded region it breaks the hydrogen bonds between the two strands c. DNA Strand Separation and the Synthesis of RNA Primers Are Necessary Before Daughter Strands of DNA Can Be Made i. DNA helicase generates positive supercoiling ahead of each replication fork so DNA gyrase (a topoisomerase type II) enzyme travels ahead of the helicase and alleviates this supercoiling ii. Single-strand binding protein binds to both of the single strands of parental DNA and prevents them from reforming a double helix so the bases within the parental strands are kept exposed and are enabled to hydrogen bond with single nucleotides iii. A short strand of RNA called and RNA primer is made by linkage of ribonucleotides via DNA primase or simple primase. 1.
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This note was uploaded on 04/07/2008 for the course BIO 325 taught by Professor Saxena during the Spring '08 term at University of Texas at Austin.

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11- DNA Replication - Chapter 11: DNA Replication I....

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