CHAPTER 8 CHAPTER 8 THE REPLICATION OF DNA 王青 200432290064 生物科学类.
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Transcript of CHAPTER 8 CHAPTER 8 THE REPLICATION OF DNA 王青 200432290064 生物科学类.
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CHAPTER 8CHAPTER 8THE REPLICATION OF DNA 王青 200432290064 生物科学类
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OUTLINEOUTLINE
• DNA polymerization • DNA replication • Action of Telomerase
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DNADNA polymerizationpolymerization
•1.The Chemistry of DNA Synthesis
•2. The Mechanism of DNA Polymerase
•3. The Replication Fork
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The Chemistry of DNA SynthesisThe Chemistry of DNA Synthesis
• deoxynucleoside triphosphates• primer:template junction• primer• Hydrolysis of pyrophosphate (PPi)• Metal ion
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back
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The Mechanism of DNA PolymeraseThe Mechanism of DNA Polymerase
Thumb
Palm
Fingers
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palmpalm
•Palm domain hydrogen bonds to base pairs in minor groove
•Hydrogen bonds only form if nucleotides are correctly base paired
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Fingers Fingers
•Finger domain associates with template region
•90 。 turn of template helps avoid confusion in the active site
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ThumbThumb
•Holds the primer:template junction in the active site
•Reduces the rate of dissociation
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• Exonucleases proofread newly synthesized DNA
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Replication fork
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DNA replicationDNA replication
• 1. The Specialization of DNA Polymerases
• 2. DNA Synthesis at the Replication Fork
• 3. Initiation of DNA Replication
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Th
e re
plic
atio
n
fork
Leading strand
Lagging strand
Okazaki fragment Replication fork
•Need the help of DNA pol ,DNA helicase, SSB, primase, DNA topoisomerase
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DNA helicse
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SSB
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DNA topoisomerase
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• DNA Pol III holoenzyme, helicase and primase interact with each other to form replisome, a finely tuned factory for DNA synthesis with the activity of each protein is highly coordinated.
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replisomereplisome
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• the trombone model for coordinating replication by two DNA polymeraes at the repolication fork
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Three differentfunctions of initiator protein: (1) binds to replicator, (2) distorts/unwinds a region of DNA, (3) interacts with and recruits additional replication factors
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Action of TelomeraseAction of Telomerase
• 1. Binding and Unwinding: origin selection and activation by the intiator protein
• 2. Finishing Replication
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Telomere replicationTelomere replication
The end of linear chromosomes can’t be fully replication by semi-discontinuous replication as there is no DNA ti elongate to replace the RNA removed from the 5’-end of the lagging strand. Thus,genetic information sould be lost from the DNA. To over come this, the ends of eukaryotic chromosomes( telomeres) consist of hundreds of copies of a simple, noninformational repeat sequence with the 3’-end overhanging the 5’-end.
The enzyme telomerase contains a short DNA molecule part of whose sequence is complementary to this repeat. This RNA acts as a template for the addition of these repeats to the 3’-overhang by repeated cycles of elongation and translocation
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Repulication of telomeres by tRepulication of telomeres by telomerase(FIGURE 8-36)elomerase(FIGURE 8-36)
• Telomerase uses its RNA component to the 3’-end of the ssDNA region of the telomere.
• Telomerase then uses its reverse transcription activity to synthesize DNA to the end of the RNA template.
• Telomerase then displaces the RNA from the DNA product and rebinds at the end of the telomere and repeats the process
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Role of Telomeres and Role of Telomeres and Telomerase in Cancer and Telomerase in Cancer and
AgingAging
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G1
G2M
S
G0
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• G1 :the longest phase during which the cells are preparing for DNA replication
• S: the only period in the cell cycle during which DNA is replication
• G2: a short gap before mitosis• M: mitosis and cell division
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• G0: cell can also exit the cell cycle after mitosis and enter a nonprotiferative state
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THANK YOUTHANK YOU