THE MOLECULAR BASIS OF INHERITANCE
DNA REPLICATION
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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DNA polymerase I can only add nucleotides from 3’
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DNA polymerase I can only add nucleotides from 5’
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DNA polymerase III can only add nucleotides from 3’
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DNA polymerase III can only add nucleotides from 5’
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Detailed explanation-1: -Why must there be a lagging strand during DNA synthesis? Explanation: The lagging strand exists because DNA is antiparallel and replication always occurs in the 5’ to 3’ direction.
Detailed explanation-2: -Helicase, primase, and two molecules of DNA polymerase III carry out coordinated synthesis of both the leading and lagging strands of DNA.
Detailed explanation-3: -The need for accuracy probably explains why DNA replication occurs only in the 5′-to-3′ direction. If there were a DNA polymerase that added deoxyribonucleoside triphosphates in the 3′-to-5′ direction, the growing 5′-chain end, rather than the incoming mononucleotide, would carry the activating triphosphate.
Detailed explanation-4: -DNA is always synthesized in the 5’ to 3’ direction because DNA polymerases can only catalyze phosphodiester bond formation (a condensation reaction) between the 3’ OH of the sugar of the last nucleotide of an existing strand and the 5’ phosphate group of the incoming nucleotide.