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It is well known that DNA polymerases synthesize DNA only in the 5' to 3' direction. Yet, at the replication fork, both strands of parental DNA are being replicated with the synthesis of new DNA. An experiment examines incorporation of radio-labeled nucleotide triphosphates in unsynchronized cells, and finds a small amount of incorporated label in DNA fragments of small size. Which of the following statements explains why the experiment is compatible with new DNA from both strands being added in the 5' to 3' direction?
A.
A different DNA polymerase replicates the complementary DNA strand as a series of small fragments.
B.
A 3' to 5' DNA polymerase is active in cells with high rates of DNA replication.
C.
DNA synthesis on complementary strand produces small 5' to 3' fragments that are continuously ligated together.
D.
DNA replication switch strands every 100 nucleotides, a detail not resolved by microscopy.
E.
DNA synthesis on the complementary strand does not use RNA primers.