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Interactive Audio Lesson
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Introduction to PCR
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Today, we are going to learn about PCR, which stands for Polymerase Chain Reaction. Can anyone tell me why we might want to amplify a gene?
We might want to study it in detail or use it in experiments!
Exactly! PCR allows us to make billions of copies of a specific DNA segment, which is vital for research and medical applications. What do you think are the main steps involved in PCR?
I think there’s heating to separate DNA, then adding something to copy it?
Correct! The process starts with denaturation, where the DNA strands are separated. We then have primer annealing and extension with a special enzyme. Remember the acronym TAE for Temperature, Annealing, and Extension during our process!
Detailed Steps of PCR
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Now let's dive deeper into those steps. What happens during denaturation?
The DNA gets heated to separate into single strands!
Exactly! And then what follows?
The primers attach to the strands.
Right! Those primers are essential because they define the target segment we want to amplify. Finally, what happens in the last stage?
The DNA polymerase extends the strands!
Perfect! This process repeats many times, multiplying the DNA exponentially. Can you remember why we use a thermostable polymerase?
Because it can withstand the high temperatures used for denaturation!
Absolutely! That’s why we specifically use Taq polymerase from the bacterium Thermus aquaticus.
Applications of PCR
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Now that we understand PCR, can anyone think of some applications in real life?
Forensics! It can help match DNA samples found at crime scenes.
Precisely! PCR is crucial in forensic science. What else?
Medical diagnostics, like detecting infections or genetic disorders!
Correct! PCR can detect diseases by amplifying the DNA from pathogens. This technique revolutionized our understanding and capabilities in many scientific fields. Let’s summarize—what are the key points about PCR?
It's a method to amplify specific DNA sequences through cycles of heating and cooling.
Yes, and its applications range from forensics to diagnostics. Great job today!
Introduction & Overview
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Quick Overview
Standard
PCR is an essential technique in molecular biology that allows the amplification of a specific segment of DNA. By using thermal cycling and specific primers, it can generate billions of copies of a targeted DNA sequence, facilitating various applications in genetics, medicine, and research.
Detailed
Amplification of Gene of Interest using PCR
PCR, or Polymerase Chain Reaction, is a revolutionary technique in molecular biology that enables the amplification of specific DNA sequences. Developed in the 1980s by Kary Mullis, PCR utilizes cycles of heating and cooling to denature DNA, anneal primers, and extend the DNA strands.
Key Steps of PCR:
- Denaturation: The double-stranded DNA is heated to about 94-98°C, which separates it into two individual strands.
- Primer Annealing: The temperature is decreased to 50-65°C to allow two short DNA primers to anneal to the complementary sequences at the start of the target DNA segment.
- Extension: The temperature is raised to 75-80°C, where a thermostable DNA polymerase extends the primers, synthesizing new DNA strands by adding nucleotides complementary to the template strand.
This cycle of denaturation, annealing, and extension is typically repeated 20-40 times, leading to an exponential increase in the number of copies of the target DNA. PCR can yield up to a billion copies of a specific DNA sequence in just a few hours.
Significance:
PCR is widely used in various fields such as genetic research, forensic science, and medical diagnostics. Its ability to precisely replicate DNA sequences makes it a fundamental tool in genetic engineering, cloning, and disease detection.
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Understanding PCR
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PCR stands for Polymerase Chain Reaction. In this reaction, multiple copies of the gene (or DNA) of interest is synthesised in vitro using two sets of primers (small chemically synthesised oligonucleotides that are complementary to the regions of DNA) and the enzyme DNA polymerase.
Detailed Explanation
PCR is a powerful technique used in molecular biology to amplify specific DNA sequences, enabling scientists to create many copies of a particular gene. This process begins with two short sequences of nucleotides known as primers, which are designed to match exactly with the ends of the target DNA sequence. The enzyme DNA polymerase then extends these primers, synthesizing new DNA strands complementary to the target template. This allows for exponential amplification of the specific DNA segment.
Examples & Analogies
Imagine you are trying to make copies of a favorite drawing. You can trace the outline with a pencil (the primer) and then use a marker (the polymerase) to fill in the details, creating a perfect replica of your drawing. With PCR, this tracing and filling process is repeated multiple times, resulting in many copies of the original drawing.
The PCR Process
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The enzyme extends the primers using the nucleotides provided in the reaction and the genomic DNA as template. If the process of replication of DNA is repeated many times, the segment of DNA can be amplified to approximately billion times, i.e., 1 billion copies are made.
Detailed Explanation
In a typical PCR cycle, there are three main steps: denaturation, annealing, and extension. Denaturation involves heating the reaction to separate the two strands of the DNA. During annealing, the temperature is lowered to allow the primers to attach to their complementary sequences on the single-stranded DNA. Finally, in the extension step, the temperature is raised again, allowing DNA polymerase to add nucleotides and synthesize a new strand of DNA from the template. This cycle is repeated around 25 to 35 times, leading to an exponential increase in the amount of the target DNA.
Examples & Analogies
Think of PCR like a photocopier that can repeatedly make copies of a document. Each cycle of PCR is like one pass of the copier; after each pass, the number of copies doubles. After several passes, you end up with an enormous stack of copies from the original document.
Role of Thermostable DNA Polymerase
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Such repeated amplification is achieved by the use of a thermostable DNA polymerase (isolated from a bacterium, Thermus aquaticus), which remain active during the high temperature induced denaturation of double stranded DNA.
Detailed Explanation
The DNA polymerase used in PCR is not like regular enzymes; it needs to withstand high temperatures used during the denaturation phase. Thermus aquaticus, a bacterium that thrives in hot springs, produces a DNA polymerase known as Taq polymerase that remains functional even at extreme temperatures. This stability allows it to catalyze DNA synthesis throughout the PCR cycles without needing to be replaced.
Examples & Analogies
Think of Taq polymerase as a marathon runner who is trained to run in the heat of a desert. While other runners might tire and need to stop for water, Taq keeps going, consistently performing its job without pause, allowing PCR to produce many copies of DNA continuously.
Final Steps of PCR
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The amplified fragment if desired can now be used to ligate with a vector for further cloning.
Detailed Explanation
Once the target DNA has been sufficiently amplified, the next step involves acquiring a cloning vector, which is a DNA molecule that can carry the amplified DNA into a host cell. The amplified DNA is combined with the vector DNA and treated with DNA ligase, an enzyme that helps to join the DNA ends together, forming recombinant DNA that can be introduced into host organisms for expression or further study.
Examples & Analogies
Imagine you have built a beautiful model of a car out of LEGO bricks (the amplified DNA). Now, you want to add this model into a playset (the vector) that allows for more creative expansions (cloning). You carefully attach your car model to the playset with strong glue (DNA ligase), allowing it to become part of a larger, interactive environment.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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PCR involves denaturation, primer annealing, and extension.
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A thermostable DNA polymerase is essential for PCR to sustain high temperatures.
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The exponential amplification of DNA is achieved through multiple cycles of the PCR process.
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PCR applications include forensics, medical diagnostics, and genetic research.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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PCR is used in forensics to analyze DNA from biological samples to identify individuals.
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Medical diagnostics utilize PCR to quickly detect infections and genetic disorders.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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To amplificate, we separate, then bind with a primer so great; extend it long, oh what a song, and billions of copies we create!
📖 Fascinating Stories
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Imagine a gardener who wants to grow a rare plant. She starts with one seed (DNA), heats the soil to separate roots (denaturation), plants small starter seeds (primers), and then watches as they grow into many plants (amplification).
🧠 Other Memory Gems
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D-A-E: Denaturation, Annealing, Extension - the steps of PCR we mention!
🎯 Super Acronyms
PCR
- Practically Create Replicates - a reminder of PCR’s purpose!
Flash Cards
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Glossary of Terms
Review the Definitions for terms.
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Term: PCR
Definition:
A laboratory technique used to amplify segments of DNA, creating millions of copies of a specific sequence.
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Term: Thermostable DNA Polymerase
Definition:
An enzyme that remains active at high temperatures, used in PCR for DNA synthesis.
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Term: Primers
Definition:
Short, chemically synthesized oligonucleotides that are complementary to the target DNA sequence and required for DNA amplification.
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Term: Denaturation
Definition:
The first step in PCR where the double-stranded DNA is heated to separate into single strands.
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Term: Annealing
Definition:
The process in which primers bind to the complementary sequences on the single-stranded DNA.
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Term: Extension
Definition:
The step in PCR where DNA polymerase adds nucleotides to the annealed primers, creating new DNA strands.