Question

DNA replicates by which of the following models? a. conservative b. semiconservative c. dispersive d. none of the above

Short answer

Answer: b. Semiconservative

Step-by-step solution

Review the different models of DNA replication

Before attempting to answer the exercise, let's briefly review each of the models of DNA replication. a. Conservative Model: In this model, the entire original (parental) double helix remains intact, and the new DNA molecule is made of all new (daughter) strands. b. Semiconservative Model: This model states that during replication, each of the two new DNA molecules consists of one parental strand and one daughter strand. c. Dispersive Model: According to this model, both parental and daughter DNA strands are interspersed along each of the two new DNA molecules after replication. d. None of the above: This option indicates that none of the above models is the correct model for DNA replication.

Identify the correct model

After reviewing the models of DNA replication, we can now determine the correct model. Semiconservative model is the correct one, meaning that every newly synthesized strand of DNA contains one strand from the parent molecule and one newly synthesized strand.

Select the correct answer

Based on our analysis, the correct model of DNA replication is: b. Semiconservative

Key concepts

Semiconservative Model

The semiconservative model of DNA replication is a fascinating concept that plays a crucial role in genetics and cell biology. In this model, when DNA replicates, each of the two resulting DNA molecules retains one of the original parental DNA strands and synthesizes a new complementary strand. This process ensures that each daughter DNA molecule has a continuous sequence from the original parent molecule.
The idea of semiconservative replication was confirmed through the famous Meselson-Stahl experiment, which demonstrated that each new DNA molecule indeed received one old and one newly synthesized strand. The experiment used different isotopes of nitrogen to label the DNA strands, which allowed scientists to distinguish between old and new strands.

• Provides genetic continuity by conserving one old strand in each new molecule.
• Supports accurate genetic information transmission from parent to offspring.
• Explains the efficiency and reliability of DNA replication in living organisms.

These unique features confirm why the semiconservative model is the widely accepted understanding of DNA replication in biology, explaining how genetic information is reliably passed down generation after generation.

Conservative Model

The conservative model of DNA replication offers a different perspective, although it is not the accepted theory. This model suggests that the original DNA molecule stays completely intact and "conserves" itself during the process of replication. Unlike the semiconservative model, this proposal indicates that one entirely new molecule is created while the original molecule remains unchanged.
In this process, it implies that after replication, the two resulting DNA molecules would consist of one with the original parental strands and the other entirely new strands. However, research, including the Meselson-Stahl experiment, disproved this model as it showed no separate existence of an original parental double helix in daughter DNA.

• Places importance on the preservation of the original DNA molecule.
• Hypothetically leads to a more straightforward doubling of DNA without intermixing parental and daughter strands.
• Ultimately not supported by scientific evidence and experimentation.

Despite its logical approach, the conservative model’s lack of experimental support led to its dismissal in favor of more accurate theories.

Dispersive Model

The dispersive model of DNA replication presents another intriguing idea, albeit not the one that DNA actually follows. This model assumes that both parental and new DNA is dispersed in short sections throughout both strands of the daughter molecules after replication. It suggests a "mosaic" structure where fragments of old and new DNA are intermingled.
This theoretical model would mean that every generation of DNA strands would consist of a complex and randomly distributed mixture of both old and new DNA segments. Although it explains a method for mixing genetic material, it lacks clear pathways for the exactitude required in genetic information transmission, upsetting the systematic and orderly replication process we observe.

• Proposes a blending of old and new DNA throughout the daughter DNA molecules.
• Theoretically generates genetic diversity at a molecular level, yet lacks precise evidence.
• Experimentally disproven due to inability to provide orderly replication explanation.

The dispersive model remains a compelling but unsubstantiated hypothesis for DNA replication, overtaken by more demonstrably accurate models like the semiconservative model.