Ch. 20 - The Molecular Revolution: Biotechnology, Genomics, and New Frontiers

Freeman - Biological Science 7th Edition

Freeman7th EditionBiological ScienceISBN: 9783584863285Not the one you use?Change textbook

Freeman 7th Edition

Ch. 20 - The Molecular Revolution: Biotechnology, Genomics, and New Frontiers

Problem 13

Chapter 20, Problem 13

If the sequence of DNA in Question 12 were amplified using 25 PCR cycles, then the amount of this DNA would be predicted to increase by -fold.

Verified step by step guidance

Step 1: Understand the concept of PCR (Polymerase Chain Reaction). PCR is a technique used in molecular biology to amplify a single or a few copies of a segment of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence.

Step 2: Recognize that PCR amplification is exponential. This means that with each cycle, the amount of DNA doubles. This is because in each cycle, the DNA strand is separated into two strands, and each of these strands is used as a template to produce two new strands of DNA.

Step 3: Calculate the fold increase in DNA after 25 cycles. Since the amount of DNA doubles with each cycle, after 25 cycles, the amount of DNA would have increased by 2^25-fold.

Step 4: Convert the exponent to a decimal number. 2^25 equals 33,554,432. So, the amount of DNA would be predicted to increase by 33,554,432-fold.

Step 5: Understand that this is a theoretical value. In reality, the efficiency of PCR is not 100%, so the actual increase in DNA may be less than this.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Polymerase Chain Reaction (PCR)

PCR is a molecular biology technique used to amplify specific DNA sequences. It involves repeated cycles of denaturation, annealing, and extension, allowing for exponential replication of the target DNA. Each cycle theoretically doubles the amount of DNA, making it a powerful tool for genetic analysis and research.

Exponential Growth in PCR

In PCR, the amount of DNA increases exponentially with each cycle. After 'n' cycles, the amount of DNA can be calculated using the formula 2^n, where 'n' is the number of cycles. Therefore, with 25 cycles, the DNA amount would increase by 2^25, illustrating the rapid amplification capability of this technique.

Limitations of PCR Amplification

While PCR can amplify DNA exponentially, there are limitations such as enzyme efficiency, reaction conditions, and the presence of inhibitors. These factors can affect the actual yield of DNA, meaning that the theoretical predictions may not always match the practical outcomes. Understanding these limitations is crucial for interpreting PCR results accurately.

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Related Practice

Potato blight causes potato plants to shrivel and rot. The disease is caused by the pathogen Phytophthora infestans, infamous for its role in Ireland's Great Potato Famine in the mid-1840s. The disease can devastate crops during wet weather, sometimes leading to total crop loss. Researchers aim to use recombinant DNA methods to transfer blight resistance genes from resistant varieties into susceptible varieties of potato.Transgenic plants usually contain genes of bacterial plasmid origin. In a recent study, researchers designed a strategy that avoided using any plasmid genes. They transformed cells from a susceptible potato variety with a potato blight resistance gene cloned from a resistant variety. Next, to determine which plants from this group were also free of plasmid DNA (cloning vector) sequences, they performed PCR using primers specific for the plasmid. The positive control lane shows PCR amplification of plasmid DNA only, and the negative control lane shows an attempted PCR amplification of no added DNA. Based on the gel analysis of PCR products shown below, which plants contain only the potato gene? Explain your answer.

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Textbook Question

Potato blight causes potato plants to shrivel and rot. The disease is caused by the pathogen Phytophthora infestans, infamous for its role in Ireland's Great Potato Famine in the mid-1840s. The disease can devastate crops during wet weather, sometimes leading to total crop loss. Researchers aim to use recombinant DNA methods to transfer blight resistance genes from resistant varieties into susceptible varieties of potato. Transgenic plants usually contain genes of bacterial plasmid origin. In a recent study, researchers designed a strategy that avoided using any plasmid genes. They transformed cells from a susceptible potato variety with a potato blight resistance gene cloned from a resistant variety. Next, to determine which plants from this group were also free of plasmid DNA (cloning vector) sequences, they performed PCR using primers specific for the plasmid. The positive control lane shows PCR amplification of plasmid DNA only, and the negative control lane shows an attempted PCR amplification of no added DNA. Based on the gel analysis of PCR products shown below, which plants contain only the potato gene? Explain your answer.

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Textbook Question

If the sequence of DNA in Question 12 were amplified using 25 PCR cycles, then the amount of this DNA would be predicted to increase by -fold.

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Textbook Question

Why was it important to include a positive control and a negative control in the PCR analysis?

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Textbook Question

Why was it important to include a positive control and a negative control in the PCR analysis?

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