Question:medium

Which one of the following statements about DNA replication is incorrect?

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In bidirectional DNA replication, the same parental strand can act as a leading-strand template at one replication fork and a lagging-strand template at the other fork. This is a frequently tested concept in molecular biology and genetics examinations.
Updated On: Jun 11, 2026
  • During DNA replication, when adjacent bidirectional forks converge, the lagging strand will meet the leading strand of the same template strand.
  • Mispaired nucleotide at the \(3'\)-OH end of the primer strand triggers the \(3' \rightarrow 5'\) exonucleolytic proofreading activity.
  • In a replication bubble moving bidirectionally, the same parental DNA strand can serve as a template for both the lagging and the leading strand synthesis.
  • DNA replication involves RNA--DNA chimeric molecules.
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The Correct Option is A

Solution and Explanation

Step 1: Know the ground rules of replication.
DNA replication is semiconservative and bidirectional. DNA polymerase can only add bases in the $5' \rightarrow 3'$ direction, so at each fork one new strand is built continuously (leading) and the other in short pieces (lagging). We must find the one statement that is incorrect.
Step 2: Examine option (A).
When two neighbouring forks moving toward each other finally meet, the leading strand made at one fork joins up with the lagging strand made at the adjacent fork. They are templated by different parental strands. The claim that the lagging strand meets the leading strand of the same template strand is therefore false.
Step 3: Examine option (B).
If a wrong nucleotide is added at the $3'$-OH end, DNA polymerase's $3' \rightarrow 5'$ exonuclease proofreading removes it and tries again. This is a real, well-known mechanism that raises fidelity, so (B) is true.
Step 4: Examine option (C).
In a bidirectional bubble, a given parental strand is read for leading-strand synthesis at one fork and for lagging-strand synthesis at the opposite fork. So the same parental strand really does template both kinds of synthesis, just at different forks. (C) is true.
Step 5: Examine option (D).
Each new fragment begins with an RNA primer laid down by primase, so the nascent strands are briefly RNA-DNA chimeric molecules until the primers are replaced by DNA. (D) is true.
Step 6: Conclude.
Statements (B), (C) and (D) are all correct, so the lone incorrect one is (A).
\[ \boxed{\text{During DNA replication, when adjacent bidirectional forks converge, the lagging strand will meet the leading strand of the same template strand.}} \]
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