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18 Cards in this Set
- Front
- Back
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Okazaki Fragments
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replication moves in only one direction, but DNA replication only goes in the 5' to 3' direction
is a discontinuous replication off the lagging strand. is a discontinuous replication off the lagging strand. DNA is replicated continuously on the leading strand. 1. |
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1. Unwinding of the DNA molecule
Enzyme responsible How? |
Helicase: unwinds the DBA ahead of the replication fork.
2 strands seperated by DNA binding proteins to prevent re-attatchment |
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What do topoisomerase enzymes do?
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cause a single stranded break to allow rotation and to relieve the induced stress of super coiling
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2. A free 3'OH group is required for replication to proceed
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When the two chains separate no 3' OH group exists. RNA primers are synthesized by the enzyme primase, and the free 3' OH group of the primer is used to begin replication
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primase complex is also known as?
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primosome
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What does DNA polymerase do?
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It catalyses the addition of nucleotides to the 3'end of DNA therefore synthesis is always in the 5' to 3' direction
Proof reads as it has 3' exonuclease activity meaning it can move backwards to remove mismatched bases. |
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What does DNA polymerase 1 do?
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RNA stretches are removed by the 5' to 3' exonuclease action of DNA Polymerase I.
Fills in gaps made by removing RNA It is a repair enzyme. |
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What does DNA ligase do?
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Seals the Okazaki fragments because DNA polymerase cant.
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Telomeres in Eukaryotic DNA
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DNA polymerase cannot synthesis the extreme 5' end of the lagging strand.
To avoid shorteneing Telomerase synthesis the terminal end of the DNA on a chromosome |
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Describe Telomerase
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Has its own internal RNA templare allowing it to sythesis the terminal DNA on a chromosomes.
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What are the ezymes that aid helicase?
And how? |
topoisomerase (DNA gyrase)
twists the helix in the direction that facilitates unwinding |
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How are the two strands kept apart?
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Single stranded DNA binding proteins
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What causes supercoils?
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The rapid unwinding and progression of the replication fork
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How are supercoils avoided?
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A single stranded break via topoisomerase (DNA gyrase) allows rotaion and relieves stress.
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When the two chainss seperate what is missing?
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3' OH group.
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How is the missing 3' OH overcome to begin replication?
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Primase synthesises RNA primers and their free 3' OH group is used to begin replication
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What is another name for the primase complex?
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Primosome
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DNA Polymerase III
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catalyses most of the DNA synthesis that occurs during DNA rep.
Has 5' → 3' exonuclease activity |
