Question 1
Multiple choiceMedium1 markPCR primers flank a 300 bp region of a DNA sample. After repeated temperature cycles, the products and a 600 bp DNA fragment are loaded into separate wells of the same gel. Which statement correctly links DNA synthesis in PCR to the relative movement of the fragments?
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Answer: C. Taq polymerase extends primers by adding nucleotides, making copies of the region between them. The 300 bp product is shorter than the 600 bp fragment, so it moves farther through the gel. A: assigns DNA synthesis to helicase and reverses the gel-size relationship; helicase unwinds strands, while the shorter fragment travels farther. B: correctly identifies polymerase synthesis but reverses the size-dependent migration. D: assigns DNA synthesis to helicase, which separates strands rather than making DNA copies. Remember: PCR copies DNA with polymerase; gel electrophoresis separates fragments by size.