Problem 6 - Biology Today and Tomorrow Without Physiology

Question

PCR can be used to _______ a. increase the number of specific DNA fragments b. check DNA fingerprints c. modify a human genome d. a and b are correct

Step-by-Step Solution

Answer

d. a and b are correct

Step 1: Understand PCR

Polymerase Chain Reaction (PCR) is a laboratory technique used to amplify DNA sequences. This means it can generate thousands to millions of copies of a particular DNA sequence starting from a small amount of DNA.

Step 2: Analyze Option (a)

Option (a) states that PCR can 'increase the number of specific DNA fragments.' By definition, PCR amplifies, or increases the number of, specific DNA fragments, and therefore, option (a) is correct.

Step 3: Analyze Option (b)

Option (b) claims PCR can be used to 'check DNA fingerprints.' PCR is indeed used in forensic science to analyze DNA samples for matching sequences, a process often referred to as DNA fingerprinting. Thus, option (b) is also correct.

Step 4: Analyze Option (c)

Option (c) asserts that PCR can 'modify a human genome.' While PCR can be used in processes that may lead to genomic modification, it itself is not responsible for modifying a genome. Therefore, option (c) is incorrect.

Step 5: Evaluate Option (d)

Option (d) suggests that both options (a) and (b) are correct. Since we have determined that both (a) and (b) are indeed correct, option (d) is the correct choice.

Key Concepts

DNA Amplification

DNA Amplification is at the heart of PCR. It refers to the process of creating multiple copies of a DNA segment.
This is especially useful when you have a small sample size and need more DNA material for analysis or experimentation. PCR, or Polymerase Chain Reaction, is the go-to technique for DNA amplification. The process of DNA amplification through PCR goes through three main phases:

• Denaturation: This is the first step where the double-stranded DNA is heated to separate it into two individual strands.
• Annealing: In this step, the temperature is lowered to allow DNA primers to attach or anneal to the beginning of the target sequence.
• Extension: Finally, the temperature is raised slightly to allow the enzyme Taq polymerase to add new nucleotides, extending the DNA strand, and replicating the target sequence.

This cycle is repeated many times (usually 25-35 cycles), resulting in exponential amplification, meaning millions of copies of the DNA can be made starting from just one template strand.

DNA Fingerprinting

DNA Fingerprinting is a vital application of PCR that helps in identifying genetic makeup. The term 'fingerprinting' is used because, much like human fingerprints, each person's DNA sequence is unique.
This makes it an invaluable tool in forensic science, paternity testing, and even biodiversity studies. In DNA fingerprinting, specific regions of the DNA that vary greatly among individuals are amplified using PCR. These regions are known as variable number tandem repeats (VNTRs) or short tandem repeats (STRs).

• Variability among these regions allows scientists to compare DNA samples from different individuals and determine relationships or matches.
• For example, in forensic investigations, DNA from a crime scene is compared with a suspect's DNA. PCR helps to amplify the DNA sample, allowing for an effective comparison.

By examining the patterns of STRs, scientists can develop a genetic profile of an individual. Due to the uniqueness of DNA, this profile can essentially serve as a biochemical ID card.

Laboratory Techniques

Laboratory Techniques are the methods and procedures used in labs to conduct experiments like PCR. Mastering these techniques is essential for reliable results. PCR is one of several key techniques used across genetics and molecular biology. In the context of PCR, the following are critical techniques and tools:

• Pipetting: Accurate pipetting is crucial to ensure the correct volume of reagents and samples. Any variance can affect the outcome significantly.
• Use of a thermal cycler: This is a machine that adjusts the temperature to carry out the cycles of denaturation, annealing, and extension in PCR efficiently.
• Preparation of reaction mixtures: This involves combining DNA templates, primers, nucleotides, and the enzyme Taq polymerase. The accuracy of quantities in these mixtures can determine the success of the amplification process.

Each step in PCR requires careful monitoring and technique application. Once you have mastered these skills, you can conduct larger experiments and contribute to significant genetic discoveries.