Molecular Genetics 2

Molecular Genetics 2 - Francke 2 10/23/08 Human Biology 2A...

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Francke 2 10/23/08 Molecular genetics II 1 10/22/08 HB2A.Molec.genetics II 1 Molecular Genetics II DNA: Replication and Repair Human Biology 2A Dr. Uta Francke Department of Genetics, SUMC ufrancke@stanford.edu 10.23.08 10/22/08 HB2A.Molec.genetics II 2 Today’s lecture • How is DNA replicated? • How are copying errors and damage to DNA repaired? 10/22/08 HB2A.Molec.genetics II 3 The Watson and Crick structure suggested a mechanism for duplicating DNA It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material. Also suggested mechanism for resisting mutations (a change on one strand can be overcome by the correct base on the other strand)
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Francke 2 10/23/08 Molecular genetics II 1 10/22/08 HB2A.Molec.genetics II 4 Steps in DNA replication • The double helix is unwound, making two template strands • New nucleotides are added to the new strand at the 3’ end; joined by phosphodiester linkages • Sequence is determined by complementary base pairing 10/22/08 HB2A.Molec.genetics II 5 DNA replication requires nucleotides, templates and primers Nucleotide triphosphates (dATP, dGTP, dCTP, dTTP) Both strands serve as templates for replication 10/22/08 HB2A.Molec.genetics II 6 Nucleotides are added to the 3’ (OH-) end
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10/23/08 Molecular genetics II 1 10/22/08 HB2A.Molec.genetics II 7 How does it actually happen? • A large protein complex—the replication complex —catalyzes the reactions of replication. • All chromosomes have a base sequence called origin of replication ( ori ) • Replication complex binds to ori at start • DNA replicates in both directions, forming two replication forks • Large linear chromosomes have many origins of replication. DNA is replicated simultaneously at the origins 10/22/08 HB2A.Molec.genetics II 8 06_09_Replic.forks.jpg 10/22/08 HB2A.Molec.genetics II 9 What happens at the replication fork? DNA helicase unwinds the DNA double helix Single-strand binding proteins keep the strands from getting back together • A primer is required to start DNA replication—a short single strand of RNA. • Primer is synthesized by
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Molecular Genetics 2 - Francke 2 10/23/08 Human Biology 2A...

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