D1.1 DNA replicationIB Biology SL: Flashcards

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What does DNA replication produce?

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What does DNA replication produce?: Two DNA molecules with base sequences identical to the original.
Give three reasons why DNA replication is needed.: Reproduction, growth and tissue replacement in multicellular organisms.
What does semi-conservative mean?: Each new molecule contains one original strand and one newly made strand.
Which bases pair in DNA?: Adenine with thymine; cytosine with guanine.
Why is replication so accurate?: Only complementary bases can pair with the template, so the new strand has the correct sequence.
Role of helicase?: Unwinds the double helix and breaks hydrogen bonds between the strands.
Role of DNA polymerase?: Links nucleotides into a new strand complementary to the template.
Meselson–Stahl result after one generation in ¹⁴N?: A single band of intermediate density — rules out conservative replication.
Three PCR temperatures and what happens?: ~95 °C strands separate; ~55 °C primers bind; ~72 °C Taq polymerase extends.
Why is Taq polymerase used in PCR?: It is heat-stable, so it is not denatured at 95 °C.
What is the job of a primer in PCR?: Binds next to the target sequence so polymerase can start copying there — it selects what is amplified.
How many copies after n PCR cycles from one molecule?: 2ⁿ (the number doubles each cycle).
Why does DNA move in a gel?: It is negatively charged (phosphates), so it moves towards the positive electrode.
Which fragments travel furthest in a gel?: The shortest ones.
Why use many markers in DNA profiling?: Each extra marker lowers the probability of a false (chance) match.