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Chapter 7-4.docx

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BIOL 2000
Joseph Rasmussen

Chapter 7- 4 Clicker question Which one of the following statements about lagging strand DNA synthesis is incorrect? a) DNA polymearase III generates an RNA primer for each Okazaki fragment produced a. Correct answer: Primase b) It requires the joining (ligation) of many Okazaki fragments c) DNA template strand is read in 3’ to 5’ direction d) IT is disconintous DNA synthesis e) All of the above are correct. Initiation of synthesis  Timing of replication in eukaryotic cell cycle is once  Timing control through Cdc6 and Cdt1 o Also ensres if only happens once o Only in G1  G1 phase o Where pre-replication complex is formed o Ready to go for synthesis o ORC+ Cdc6 + Cdt1 + Helicase  Helicase is required for replication to occur for “lining up”  The other proteins inhibit Helicase from proceeding  Prevents synthesis from occurring  S phase o Helicase is activated  Cdc6 degraded  Cdt1 inhibited o Replication forks are made from helicase  G2 gap phase happens after synthesis The Replisome  All the components required for DNA replication o Main Functions  Progressively unwind the helix and keep strands separated  Catalyze main DNA synthesis (phosphodiester bond formation) on both leading and lagging strands  Add on DNTP  Need to synthesize both strands at the same time  Lagging strand needs Okazaki fragment formation  Join the Okazaki fragments Replisome at work  Main polymerase components o Where most of DNA synthesis is occurring  2 associated DNA polymerase III complexes  To read both strands at the same time  Beta Clamp for processivity  Clamping DNA polymerase to DNA strand  DNA looping (for lagging strand synthesis)  Synthesis must move in opposite direction of the replication fork  Pulls the DNA strand through the polymerase in the bottom, out the top for lagging strand  Primase for lagging strand synthesis  Every Okazaki fragment requires a primer o Exam question  What are the specific functions of the components?  Unwinding components o Helicase  Strand separation  Actively unwind the strands o Single stranded binding proteins  Prevents the strands from coming back toget
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