Question

\(\mathrm{PCR}\) a. uses RNA polymerase. b. takes place in huge bioreactors. c. uses DNA replication in vitro. d. makes many nonidentical copies of DNA. e. All of these are correct.

Short answer

The correct statement is: \(c. PCR \) uses DNA replication in vitro.

Step-by-step solution

Analyze statement (a)

PCR uses RNA polymerase. This statement is incorrect. PCR uses DNA polymerase, not RNA polymerase, to replicate DNA.

Analyze statement (b)

PCR takes place in huge bioreactors. This statement is also incorrect. PCR takes place in a small instrument called a thermocycler, which precisely changes temperature during the PCR process.

Analyze statement (c)

PCR uses DNA replication in vitro. This statement is correct. PCR is an in vitro (test tube) method that is used to amplify specific DNA sequences.

Analyze statement (d)

PCR makes many nonidentical copies of DNA. This statement is incorrect. PCR makes many identical copies of a specific DNA sequence, not nonidentical copies.

Analyze statement (e)

All of these are correct. Since not all of the above statements are correct, this statement is incorrect.

Conclusion

Based on our analysis, the correct statement is: c. PCR uses DNA replication in vitro.

Key concepts

DNA polymerase

DNA polymerase is an enzyme that is crucial in the process of DNA replication during Polymerase Chain Reaction (PCR). This enzyme reads the original DNA strand and synthesizes a new complementary strand by adding nucleotides. Unlike RNA polymerase, which synthesizes RNA from a DNA template, DNA polymerase creates a new DNA strand.
One of the key features of DNA polymerase used in PCR is its ability to withstand high temperatures, as the DNA must be denatured (or split into two single strands) using heat. This heat resistance is found in Taq polymerase, an enzyme isolated from the thermophilic bacterium, Thermus aquaticus, which thrives in hot environments. This unique property makes it ideal for the repetitive heating and cooling cycles in PCR.

DNA replication

DNA replication is a fundamental process through which a cell duplicates its DNA, ensuring that each new cell receives an identical copy during cell division. In the context of PCR, this process is replicated artificially in a test tube or small machine known as a thermocycler.
The replication involves several steps:

• Denaturation: The DNA double helix is heated to separate it into two single strands.
• Annealing: The temperature is lowered to allow primers to attach to the DNA template strands.
• Extension: DNA polymerase extends the primers to form a new DNA strand.

Each cycle of these three steps results in a doubling of the DNA molecule, leading to exponential growth of the DNA sequence being replicated.

Amplification of DNA

Amplification of DNA is the main goal of PCR. This process involves repeatedly copying a specific segment of DNA to produce millions of copies from a small initial amount. PCR achieves this rapid and significant multiplication through its cycling of denaturation, annealing, and extension.
The efficiency and specificity of the PCR amplification depend on various factors:

• Selection of primers that match the target DNA sequence.
• Optimal temperature settings for each step of the cycle.
• The quality and activity of the DNA polymerase.

Because of its ability to produce large amounts of specific DNA segments quickly, PCR is invaluable in fields such as forensic science, medical diagnostics, and genetic research.

In vitro techniques

In vitro techniques refer to processes performed outside a living organism, typically in a controlled laboratory environment, such as test tubes or petri dishes. PCR is a quintessential example of an in vitro technique, as it replicates the natural cell DNA replication process outside a living cell.
Performing such techniques provides several advantages:

• Precise control over experimental conditions such as temperature and reagent concentrations.
• The ability to perform experiments without the complexity and unpredictability of a living organism.
• High-throughput capabilities, allowing many experiments or replications to be conducted simultaneously.

These features have made in vitro techniques essential in biotechnology, molecular biology, and biomedical research, providing a platform for precise manipulation and study of cellular processes.