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212_Enger-2011-09-23-stdt

212_Enger-2011-09-23-stdt - Telomeres and Telomerase...

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9/21/10 1 Telomeres and Telomerase Biology 212 September 22, 2010 Telomeres and Telomerase Outline: 1. DNA replication leading and lagging strand synthesis 2. Telomeres 3. Telomerase DNA replication: First step is to separate the two strands This requires breaking the hydrogen bonds that hold the two complementary strands together Origin of replication: Place on DNA where DNA replication begins. Helicases: Enzymes that unwind DNA at replication forks Single-stranded binding proteins: keep the two strands from reforming hydrogen bonds with each other. Each new strand of DNA is synthesized 5’ to 3’ by the enzyme DNA polymerase
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9/21/10 2 1. Helicase 2. Single-stand binding protein 3. Primase synthesizes a short RNA primer, using the parental DNA strand as a template Starting from the RNA primer, DNA polymerase makes the new DNA strand 5’ to 3’ Comparing Leading Strand and Lagging Strand Leading strand: RNA primer is near the origin of replication. DNA synthesis can follow the replication fork. Lagging strand: RNA primer forms near the replication fork. DNA synthesis is towards the origin of replication. 5’ 5’ 3’ 3’ The steps of DNA replication At origin of replication, break the hydrogen bonds between the two strands. Make RNA primers for both strands. DNA polymerase makes a new strand in the 5’ to 3’ direction (direction refers to polarity of the NEW strand.)
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9/21/10 3 5’ 5’ 3’ 3’ 5’ 3’ 5’ 3’ At origin of replication, break the hydrogen bonds between the two strands.
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