IB›IB Biology SL›Mind mapsD1.1 DNA replicationIB Biology SL: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsWhy replicate?Makes exact copies with identical base sequencesHappens before cell divisionNeeded for reproduction and gametesNeeded for growth and tissue replacementSemi-conservativeEach new molecule: one old, one new strandOld strands act as templatesA pairs with T; C pairs with GComplementary pairing makes copying accurateMeselson-Stahl used ¹⁵N then ¹⁴NEnzymesHelicase unwinds the double helixHelicase breaks hydrogen bonds between basesDNA polymerase links free nucleotidesNew strand is complementary to templateDNA replicationcopying the genomeATCGPCRAmplifies a chosen sequence: millions of copies95 °C: strands separate55 °C: primers bind72 °C: Taq polymerase extends primersn cycles give 2ⁿ copiesGel electrophoresisSeparates DNA fragments by lengthDNA is negative, moves to positive electrodeShorter fragments move faster and furtherKnown-length fragments act as a scaleExam tipsSemi-conservative: strands wholly old or newIn PCR, heat separates strands, not helicaseTaq polymerase is heat-stableA DNA match does not prove guiltMore STR markers cut false-match chance