Question:
Which one of the following statements about DNA replication is incorrect?
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
Concept:
DNA replication is a semiconservative and bidirectional process. Replication begins at an origin and proceeds in opposite directions through two replication forks. Because DNA polymerase can synthesize DNA only in the \(5' \rightarrow 3'\) direction, one strand is synthesized continuously (leading strand) while the other is synthesized discontinuously (lagging strand).
To determine the incorrect statement, let us examine each option carefully.
Step 1: Analyze Option (A). During bidirectional replication, two replication forks move away from the origin in opposite directions. When adjacent replication forks eventually meet, the following occurs:
• A leading strand synthesized at one fork joins a lagging strand synthesized at the neighboring fork.
• The lagging strand does
not meet the leading strand synthesized on the same template strand.
Therefore the statement ``the lagging strand will meet the leading strand of the same template strand'' is incorrect. Hence, Option (A) is false.
Step 2: Analyze Option (B). DNA polymerases possess proofreading activity. If an incorrect nucleotide is incorporated at the growing \(3'\)-end, the enzyme detects the mismatch and removes it through: \[ 3' \rightarrow 5' \] exonuclease activity. This proofreading mechanism greatly increases replication fidelity. Therefore Option (B) is correct.
Step 3: Analyze Option (C). In bidirectional replication, each parental strand serves as a template. At one replication fork, a parental strand may function as the template for leading strand synthesis, while at the opposite fork the same parental strand functions as the template for lagging strand synthesis. Thus the same parental DNA strand can indeed serve as a template for both leading and lagging strand synthesis at different replication forks. Therefore Option (C) is correct.
Step 4: Analyze Option (D). DNA replication begins with RNA primers synthesized by primase. Initially, newly synthesized strands contain both RNA and DNA segments, producing temporary RNA--DNA hybrid (chimeric) molecules. After replication, RNA primers are removed and replaced with DNA. Therefore Option (D) is also correct.
Step 5: Final conclusion. Among the given statements:
• Option (B) is correct.
• Option (C) is correct.
• Option (D) is correct.
• Option (A) is incorrect.
Hence the incorrect statement is \[ \boxed{\text{(A)}} \]
Step 1: Analyze Option (A). During bidirectional replication, two replication forks move away from the origin in opposite directions. When adjacent replication forks eventually meet, the following occurs:
• A leading strand synthesized at one fork joins a lagging strand synthesized at the neighboring fork.
• The lagging strand does
not meet the leading strand synthesized on the same template strand.
Therefore the statement ``the lagging strand will meet the leading strand of the same template strand'' is incorrect. Hence, Option (A) is false.
Step 2: Analyze Option (B). DNA polymerases possess proofreading activity. If an incorrect nucleotide is incorporated at the growing \(3'\)-end, the enzyme detects the mismatch and removes it through: \[ 3' \rightarrow 5' \] exonuclease activity. This proofreading mechanism greatly increases replication fidelity. Therefore Option (B) is correct.
Step 3: Analyze Option (C). In bidirectional replication, each parental strand serves as a template. At one replication fork, a parental strand may function as the template for leading strand synthesis, while at the opposite fork the same parental strand functions as the template for lagging strand synthesis. Thus the same parental DNA strand can indeed serve as a template for both leading and lagging strand synthesis at different replication forks. Therefore Option (C) is correct.
Step 4: Analyze Option (D). DNA replication begins with RNA primers synthesized by primase. Initially, newly synthesized strands contain both RNA and DNA segments, producing temporary RNA--DNA hybrid (chimeric) molecules. After replication, RNA primers are removed and replaced with DNA. Therefore Option (D) is also correct.
Step 5: Final conclusion. Among the given statements:
• Option (B) is correct.
• Option (C) is correct.
• Option (D) is correct.
• Option (A) is incorrect.
Hence the incorrect statement is \[ \boxed{\text{(A)}} \]
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