What is the implication of the semiconservative type of replication? A. Each of the new double-stranded DNA molecules contains one of the old original strands and one newly synthesized strand. B. One of two newly synthesized double-stranded DNA molecules contains both the old original strands, and the other contains both newly synthesized strands. C. Both the newly synthesized DNA molecules have DNA segments belonging to the old strands and segments that are newly synthesized. D. None among the given is correct. 2. What does the Meselson and Stahl experiment prove? A. The type or mechanism of DNA replication is semi-conservative. B. The synthesis of the DNA strands is always 5′ to 3′. C. The 15N nitrogen source is denser than the 14N nitrogen source in the replication process. D. All of the given are correct. 3. Which of the following does not describe the mechanism of DNA replication? A. One strand is synthesized 5′ to 3′, and the other 3′ to 5′. B. The DNA undergoes strand separation. C. The synthesis is bidirectional from the site of origin of replication. D. There is fidelity and faithful copy of the original DNA in the replication process. 4. Which of the following is not a universal feature of DNA replication? A. For every nucleoside triphosphate substrate used, inorganic pyrophosphate (PPi) is hydrolyzed off. B. The synthesis of the chain in both strands follows the 5′ to 3′ direction. C. The standard base pairing of T with A and C with G is followed. D. All the given are features of DNA synthesis.
- What is the implication of the semiconservative type of replication? A. Each of the new double-stranded DNA molecules contains one of the old original strands and one newly synthesized strand. B. One of two newly synthesized double-stranded DNA molecules contains both the old original strands, and the other contains both newly synthesized strands. C. Both the newly synthesized DNA molecules have DNA segments belonging to the old strands and segments that are newly synthesized. D. None among the given is correct. 2. What does the Meselson and Stahl experiment prove? A. The type or mechanism of DNA replication is semi-conservative. B. The synthesis of the DNA strands is always 5′ to 3′. C. The 15N nitrogen source is denser than the 14N nitrogen source in the replication process. D. All of the given are correct. 3. Which of the following does not describe the mechanism of DNA replication? A. One strand is synthesized 5′ to 3′, and the other 3′ to 5′. B. The DNA undergoes strand separation. C. The synthesis is bidirectional from the site of origin of replication. D. There is fidelity and faithful copy of the original DNA in the replication process. 4. Which of the following is not a universal feature of DNA replication? A. For every nucleoside triphosphate substrate used, inorganic pyrophosphate (PPi) is hydrolyzed off. B. The synthesis of the chain in both strands follows the 5′ to 3′ direction. C. The standard base pairing of T with A and C with G is followed. D. All the given are features of DNA synthesis.
The Correct Answer and Explanation is:
Here are the correct answers with explanations:
- What is the implication of the semiconservative type of replication?
✅ Answer: A. Each of the new double-stranded DNA molecules contains one of the old original strands and one newly synthesized strand. - What does the Meselson and Stahl experiment prove?
✅ Answer: A. The type or mechanism of DNA replication is semi-conservative. - Which of the following does not describe the mechanism of DNA replication?
✅ Answer: A. One strand is synthesized 5′ to 3′, and the other 3′ to 5′. - Which of the following is not a universal feature of DNA replication?
✅ Answer: D. All the given are features of DNA synthesis.
Explanation
DNA replication is essential for cell division, ensuring that each daughter cell receives an exact copy of the genetic material. The semiconservative model of replication, proven by Meselson and Stahl in 1958, describes how DNA duplicates: each of the two resulting DNA molecules retains one original (parental) strand and synthesizes a new complementary strand. This is correctly described by Option A in question 1 and confirmed in question 2. The Meselson-Stahl experiment used isotopes of nitrogen (^15N and ^14N) to label DNA strands and showed intermediate-density DNA after one replication cycle, consistent only with the semiconservative model.
In question 3, the incorrect description is Option A, which suggests one strand is synthesized 3’ to 5’. In reality, DNA polymerases can only add nucleotides in the 5’ to 3’ direction. To cope with this on the antiparallel template strands, the leading strand is synthesized continuously, while the lagging strand is synthesized discontinuously in short fragments called Okazaki fragments, both in the 5’ to 3’ direction.
In question 4, Option D is correct because all the given statements are indeed universal features of DNA replication. These include the hydrolysis of pyrophosphate (PPi) for energy during nucleotide addition, consistent 5′ to 3′ synthesis direction, and standard Watson-Crick base pairing (A with T, C with G).
Together, these principles highlight the precision, directionality, and energy requirements of DNA replication, crucial for maintaining genetic fidelity across generations.
