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20 Cards in this Set
- Front
- Back
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What is DNA polymerase?
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Enzyme that catalyzes the stepwise addition of a deoxyribonucleotide to the 3' end of the growing nucleotide chain called the primer strand
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What is the structure of DNA polymerase?
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Resembles a right hand, in which the palm, fingers and thumb grasp the DNA to form the active site
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How does DNA pol work?
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-Correct positioning of the deoxyribonucleotide triphosphate causes the fingers of the polymerase to tighten, initiating the chemical reaction that is the addition of the nucleotide
-dissociation of the pyrophosphate causes release and translocation of DNA |
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How long are Okazaki fragments in bacteria?
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1000-2000 nucleotides in length
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How long are Okazaki fragments in eukaryotes?
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100-200 nucleotides
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What is the fidelity of DNA replication?
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1 mistake in 10^9 nucleotides
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How the fidelity of DNA replication achieved?
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1. Affinity of incoming nucleotide to the polymerase is checked by proper b-pairing to template strand.
2. Polymerase double checks the exact base-pair geometry via conformational change 3. Exonucleolytic proofreading |
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What is exonucleolyric proofreading?
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mechanisms that occurs in the rare case when an incorrect nucleotide is added, conducted by a 3'-5' proofereading exonuclease that removes any unpaired residue- in a separate catalytic site that is in another subunit of the polymerase
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Is DNA polymerase a self correcting enzyme?
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Yes
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What does DNA primase do?
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Can start a polynucleotide chain by joining 2 ribonucleoside triphosphates on a DNA template, needed because DNA pol cannot perofrm de novo synthesis
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What does DNA ligase do?
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Seals what amounts to a broken phosphodiester bone
-Uses a molecule of ATP to activate the 5' end fof the nick -Forms the new phosphodiester bone and AMP is released |
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How strong is base pair H-bonding in the DNA double helix?
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Temperatures near that of boiling water are required to separate the 2 strands
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What does DNA helicase do?
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Opens the double helix
Couples the hydrolysis of ATP to the opening of the double helix in front of the replication form Uses ATP hydrolysis to move along a particular strand |
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How fast does DNA helicase open the helix?
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1000 nucleotide pairs/sec
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What do single-strand DNA binding proteins do?
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Provide the single stranded DNA template for DNA pol to copy, bind tightly and cooperatively to expose ss DNA making it available for templating
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What is the structure of helicase?
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Hexamer
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What does cooperative protein binding do?
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Straightens region of chain- prevent formation of short hairpin helixes on DNA which can impede replication
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What is the sliding clamp?
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A protein that holds the moving DNA pol on the DNA for continuous synthesis
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How does the sliding clamp work?
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Sliding clamp holds onto moving polymerase and the whole ring slides freely along the DNA molecule as the polymerase moves
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How is the sliding clamp assembled?
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Requires ATP hydrolysis by a special clamp loading protein
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