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Proofreading Function of DNA Polymerase

How does DNA polymerase use the structure of DNA to catch errors? DNA polymerase moves along a single strand of DNA, building the complementary strand as it goes. The two stranded molecule passes through the DNA polymerase molecule after synthesis is complete. If the wrong base is inserted then the bond is unstable. Because the double strand is passing through the DNA polymerase the missing base can be detected and replaced. The replacement is done by a different part of the enzyme. If DNA polymerase did use single stranded DNA as a template and the completed double strand did not continue to interact with the enzyme after synthesis then the number of errors in DNA replication would be much higher.

View the animation below, then complete the quiz to test your knowledge of the concept.

1The proofreading function of DNA polymerase reduces the error rate from about one in a million basepairs to about one in a ________ basepairs.
A)hundred thousand
B)ten thousand
D)ten million
E)hundred million

2DNA polymerases use their ________ activity to remove a mismatched basepair.
A)3’ -> 5’ exonuclease
B)5’ -> 3’ exonuclease

3Proofreading by DNA polymerase involves the removal of
A)only the mismatched base on the old strand of DNA.
B)only the mismatched base on the newly-synthesized strand of DNA.
C)the mismatched basepair on both strands of DNA.
D)several bases on the newly-synthesized strand of DNA.
E)several bases on the old strand of DNA.

4Improper base-pairing during DNA replication causes a pause in chain elongation.

5Following base removal, DNA polymerase can add nucleotides in the 5’ to 3’ direction.

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