You Should Be Able To

Transcription

1 DNA Replica,on

2 You Should Be Able To 1. Describe the func9on of: DNA POL1, DNA POL3, Sliding Clamp, SSBPs, Ligase, Topoisomerase, Helicase, Primase 2. Describe DNA synthesis on the leading and lagging strand. 3. Draw a diagram illustra9ng DNA replica9on. [StraighKorward model, or replisome] 4. Describe how telomerase helps protect linear chromosomes during replica9on.

3 DNA s structure naturally lends itself to being replicated

4 Fig A T G C T A T A G C (a) Parent molecule A T G C T A T A G C (c) Daughter DNA molecules, each consisting of one parental strand and one new strand (b) Separation of strands A T G C T A T A G C A T G C T A T A G C

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7 DNA POL III Sliding Clamp Helicase DNA POL III Sliding Clamp

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9 Helicase

10 Figure 14-8 Slide 1 1. DNA is opened, Helicase opens double helix

11 Figure 14-8 Slide 1 1. DNA is opened, Helicase opens double helix

12 Single Strand Binding Proteins

13 Figure 14-8 Slide 2 1. DNA is opened, Helicase opens double helix Single-strand DNA-binding proteins (SSBP) stabilize single strands

14 Topoisomerase

15 Figure 14-8 Slide 3 1. DNA is opened, unwound, Topoisomerase relieves twisting forces Helicase opens double helix Single-strand DNA-binding proteins (SSBP) stabilize single strands

16 Primase

17 Figure 14-8 Slide 4 1. DNA is opened, unwound, and primed. Primase synthesizes RNA primer Topoisomerase relieves twisting forces Helicase opens double helix Single-strand DNA-binding proteins (SSBP) stabilize single strands

18 Figure 14-8 Slide 5 2. Synthesis of leading strand begins. RNA primer Leading strand

19 DNA Polymerase III + Sliding Clamp

20 Figure 14-8 Slide 6 2. Synthesis of leading strand begins. RNA primer Leading strand Sliding clamp holds DNA polymerase in place DNA polymerase III works in 5ʹ 3ʹ direction, synthesizing leading strand

21 DNA POL III

22 Leading strand synthesized 5ʹ 3ʹ Lagging strand synthesized 5ʹ 3ʹ How is this growing gap filled in?

23 Figure Slide 2 RNA primer The leading strands are faded out to help you focus on synthesis of the lagging strand SSBPs Primase Helicase Topoisomerase 1. Primer added. Primase synthesizes RNA primer.

24 Figure Slide 3 Okazaki fragment Sliding clamp DNA polymerase 2. First fragment synthesized. DNA polymerase III works in 5ʹ 3ʹ direction, synthesizing first Okazaki fragment of lagging strand.

25 Figure Slide 4 2nd Okazaki fragment 1st Okazaki fragment 3. Second fragment synthesized. Primase and DNA polymerase III synthesize another Okazaki fragment.

26 DNA Polymerase I

27 Figure Slide 5 DNA polymerase I 4. Primer replaced. DNA polymerase I removes ribonucleotides of primer, replaces them with deoxyribonucleotides in 5ʹ 3ʹ direction.

28 Okazaki Fragments

29 Ligase

30 Figure Slide 6 DNA ligase 5. Gap closed. DNA ligase closes gap in sugar-phosphate backbone.

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32 DNA POL III Sliding Clamp Helicase DNA POL III Sliding Clamp

33 DNA POL III Sliding Clamp Topoisomerase Helicase Primase Ligase

34 A Complica9on Prokaryotes have a circular chromosome. Eukaryotes do not.

35 Ends of parental DNA strands 5ʹ 3ʹ Leading strand Lagging strand 3ʹ 5 Last fragment Previous fragment DNA Pol1 Can only add nucleo9des to the 3 end of exis9ng DNA. Telomeres protect an organism s genes from being eroded during successive rounds of DNA replica9on. In humans the sequence TTAGGG is repeated between 100 and mes. Lagging strand 5ʹ RNA primer 3ʹ Parental strand 3ʹ New leading strand New lagging strand 3ʹ 5ʹ 5ʹ 3ʹ 5ʹ Removal of primers and replacement with DNA where a 3ʹ end is available Second round of replication Further rounds of replication Shorter and shorter daughter molecules

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37 You Should Be Able To 1. Describe the func9on of: DNA POL1, DNA POL3, Sliding Clamp, SSBPs, Ligase, Topoisomerase, Helicase, Primase 2. Describe DNA synthesis on the leading and lagging strand. 3. Draw a diagram illustra9ng DNA replica9on. [StraighKorward model, or replisome] 4. Describe how telomerase helps protect linear chromosomes during replica9on.

38 DNA Replica,on