In which direction can DNA polymerase I proofread while laying down a new nucleotide strand?

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Study for the DNA Replication and DNA Storage Test. Use flashcards and multiple choice questions, each with hints and explanations. Prepare for your exam with confidence!

Multiple Choice

In which direction can DNA polymerase I proofread while laying down a new nucleotide strand?

Explanation:
DNA polymerases add new nucleotides in the 5’ to 3’ direction, but their proofreading uses a 3’ to 5’ exonuclease activity. This means the enzyme can backtrack from the 3’ end of the growing strand and remove mispaired nucleotides in the 3’→5’ direction, correcting errors before continuing synthesis. After the incorrect nucleotides are excised, synthesis resumes in the correct 5’→3’ direction. So proofreading occurs moving from the growing 3’ end toward the 5’ direction, not in the direction of synthesis.

DNA polymerases add new nucleotides in the 5’ to 3’ direction, but their proofreading uses a 3’ to 5’ exonuclease activity. This means the enzyme can backtrack from the 3’ end of the growing strand and remove mispaired nucleotides in the 3’→5’ direction, correcting errors before continuing synthesis. After the incorrect nucleotides are excised, synthesis resumes in the correct 5’→3’ direction. So proofreading occurs moving from the growing 3’ end toward the 5’ direction, not in the direction of synthesis.

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