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Lecture 3 MCB 121

Lecture 3 MCB 121 - Lec 3 DNA Replication I Basic Rules of...

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Lec 3 01/11/11: DNA Replication I. Basic Rules of DNA Replication 1. initiates at specific sequences (origin of replication) 2. synthesis is initiated from primer (usually RNA) 3. strands are elongated in the 5’ 3’ direction by addition of mononucleotides - relative to synthesized strand 4. semi-discontinuous (leading and lagging strand synthesis) – one strand that is the leading strand that is continuous, no interruption in synthesis of the leading strand, leading strand syn is continuous where lagging strand synthesis is discontinuous because of okazaki fragments 5. semiconservative (both Watson and Crick strands are used as a template for polymerization) – if we have the parent double helix conservative means that each strand of the double helix remains intact so it is conservative. The nonconservative strand is that one of each strand is distributed to each daughter molecule. (Semiconservative because strand is retained in different daughters.) Conserves one strand of the parental and one of each daughter. Sister chromatids held together by cohesions 6. requires factors in addition to DNA polymerase PICTURE 1 -Leading strand created – is continuous -Lagging strand created - is discontinuous with RNA primer and nicks. RNA primer is removed by RNAse H or flap endoneuclease. The RNAse H degrades RNA strand of RNA/DNA duplex. Then we fill in the space with DNA sequence and repairs nicks by DNA ligase which recreates phosphodiester backbone of DNA. List of factors a. Primase – put down RNA primer + a little bit of DNA synthesis. Creates RNA primers b. DNA Polymerases Synthesis; nucleotide addition . c. processivity factors (clamp and clamp loader) – help polymerase be processive. Is enabled by the sliding clamp. PIC 2 d. Helicase unwind duplex dna so polymerase can come through. e. Replication protein A - single stranded DNA binding protein (ssb)- keeps ssDNA from folding back on itself. Binds ssDNA on lagging strand after passage of the helicase f. flap endonuclease (or RNase H) – mentioned above g. topoisomerases
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II. Enzymology
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Lecture 3 MCB 121 - Lec 3 DNA Replication I Basic Rules of...

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