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21 Cards in this Set
- Front
- Back
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What is meant by DNA replication being a semi-conservative model? |
One double helix serves as a template for two new identical double helices ....with each new double helix having one strand from the old double helix and one newly synthesised strand what is the |
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What is the leading strand? |
The continuous strand of the replication fork |
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What is the lagging strand? |
The discontinuous strand of the replication fork Okazaki fragments |
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What is DNA |
Double stranded molecule with strands of opposite polarity Held together by hydrogen bonding between bases |
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Give brief overview of replication in prokaryotes |
Usually bidirectional 260bp sequence in E.Coli Initiated by DNaA in E.coli DNA is 5’ to 3’ so template 3’ to 5’ |
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What does DNaA do? |
Initiates replication |
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What does DNaA Helicase do? |
Unwinds DNA (100,000 no/min) |
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What does Topoisomerase (gryase) do? |
Relieves supercoiling caused by helicase |
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What does Single-strand Binding Protein (SSB) do? |
Binds to expose bases |
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Define the 3 essential properties common to all DNA polymerases |
Unable to separate the two DNA strands that are to be copied Can only elongate a pre-existing DNA or RNA strands and unable to initiate chains Catalyze nucleotide addition at the 3-Hydroxyl end of a growing chain...therefore strand grown in a 5’ to 3’ direction |
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What does Polymerase 3 do? (PolIII) |
Synthesizes leading and lagging strands (synthesis most of the DNA) With a high fidelity |
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What is proofreading and editing by DNA polymerase? |
In the 3’ to 5’ direction with exonuclease...read more into it |
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The problems with replication I. Eukaryote |
Chromosomal ends Packaging DNA in the nucleus |
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Where does replication start? |
Replication fork |
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What is replication? |
Semi-discontinuous |
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What are the basics of DNA replication? |
Always synthesised in 5’ to 3’ Therefore template is always 3’ to 5’. One direction is leading the other is lagging (short fragments) |
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What is condensation? |
The process of how DNA is packaged |
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Explain the levels of condensation |
Nucleosomes 30nm fibre Scaffold associated Different regions condensed to different levels at different times |
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Describe nucleosomes |
Used positively charged histones H2A,B H3,4 DNA wrapped around complex of eight histone molecules One takes 146bp of DNA BEADS (HISTOSOMES?) |
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Describe the 30nm fibre in condensation |
Six nucleosomes arranges in a coil Needs HISTONE H1 |
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What does the 30nm protect? |
The scaffold and attaches every 45,000 to 90,000 bps |
