D1.1 DNA replicationIB Biology HL: Flashcards

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Why is DNA replication needed?

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Why is DNA replication needed?: Reproduction, growth and tissue replacement — each new cell needs an exact copy.
What is semi-conservative replication?: Each new DNA molecule has one original strand and one new strand.
Role of helicase?: Unwinds the helix and breaks hydrogen bonds between the strands.
Three PCR steps?: ~95 °C separate strands; ~55 °C primers bind; ~72 °C Taq polymerase extends.
Basis of separation in gel electrophoresis?: Negatively charged DNA moves to the positive electrode; shorter fragments move further.
Why use more markers in DNA profiling?: Fewer false matches — the chance probability falls with every marker.
HL: In which direction are new DNA strands made?: 5' to 3' — nucleotides are added to the 3' end.
HL: Which end of a new nucleotide is linked to the strand?: Its 5' end (phosphate) is linked to the 3' end of the strand.
HL: Leading strand?: Made continuously towards the fork; one RNA primer.
HL: Lagging strand?: Made discontinuously away from the fork as Okazaki fragments; many RNA primers.
HL: Role of DNA primase?: Makes short RNA primers for DNA polymerase III to extend.
HL: Role of DNA polymerase I?: Removes RNA primers and replaces them with DNA.
HL: Role of DNA ligase?: Joins Okazaki fragments by sealing the sugar-phosphate backbone.
HL: How does DNA polymerase III proofread?: Removes a mismatched nucleotide from the 3' terminal and replaces it with the correct one.
HL: Mutant lacking ligase — what accumulates?: Unjoined Okazaki fragments (with primers already replaced by DNA).