AP Biology Quiz
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CHEMISTRY OF LIFE
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A student builds a model of double-stranded DNA showing antiparallel strands: one strand runs 5'→3' while the complementary strand runs 3'→5'. Each nucleotide has a sugar with a 3' hydroxyl group and a 5' phosphate group; adjacent nucleotides are connected by phosphodiester bonds between the 3' OH and 5' phosphate. The student then tries to extend one strand by adding a nucleotide to the end. Which feature best explains why nucleotides can be added only to the 3' end of a growing DNA strand?
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