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M
Megan
09/12/2025
Biology
1.2 REPLICATION OF DNA
291
•
9 Dec 2025
•
Understanding DNA Replication and PCR
M
Megan
@megan_bnbx
1 / 4
How PCR Actually Works
PCR is basically a molecular photocopier that can amplify target sequences of DNA millions of times over. The magic happens through repeated cycles , and here's the brilliant bit - the number of copies doubles each time, following the formula 2^n where n equals the number of cycles.
Each PCR cycle has three precise temperature steps. First, the DNA gets heated to 92-98°C, which breaks hydrogen bonds between base pairs and separates the double strands - imagine unzipping a zip.
Next, cooling to 50-65°C allows primers to bind to their target sequences on the separated strands. Finally, heating to 70-80°C lets the star of the show - heat-tolerant DNA polymerase - get to work replicating the target sequence.
Mind-Blowing Fact: After just 30 cycles, you'll have over a billion copies of your original DNA sequence!
The Lagging Strand Challenge
Here's where DNA replication gets a bit tricky - not all strands can be copied the same way! The lagging strand faces a unique problem because DNA polymerase (the copying enzyme) can only add nucleotides in one specific direction.
Unlike its partner (the leading strand), the lagging strand cannot be replicated continuously. Instead, it gets copied in short chunks called fragments - think of it like writing backwards, one word at a time rather than flowing sentences.
The process requires several primers to be added at different points along the replication fork. DNA polymerase then builds each fragment separately, working in its preferred direction. Finally, the enzyme ligase acts like molecular glue, joining all the fragments together into one complete strand.
Memory Trick: Think "lagging = lagging behind = needs fragments" to remember this tricky process!
What You Need for PCR
Think of PCR like a recipe - miss one ingredient and the whole thing fails! You need five essential components in your PCR tube: the target DNA sequence you want to copy, primers (short DNA fragments that kickstart the process), DNA nucleotides (the building blocks), enzymes to do the actual copying, and a pH buffer to keep conditions stable.
Scientists use control experiments to prove each component is necessary. For instance, if they want to show primers are essential, they'll run one tube with all ingredients except primers - and surprise, no DNA copies are made!
PCR has some pretty amazing real-world applications that you've probably seen on TV crime shows. It helps solve crimes by analysing tiny DNA samples, settles paternity disputes, and can diagnose genetic disorders before symptoms even appear.
Quick Tip: PCR is often paired with gel electrophoresis, which sorts DNA fragments by size using an electrical current - like a molecular sorting machine!
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This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
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very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
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I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
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THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
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This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
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The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
Understanding DNA Replication and PCR
M
Megan
@megan_bnbx
Ever wondered how scientists can make millions of copies of DNA from just a tiny sample? PCR (Polymerase Chain Reaction) is the brilliant technique that makes this possible, and it's absolutely crucial for everything from solving crimes to diagnosing diseases.
How PCR Actually Works
PCR is basically a molecular photocopier that can amplify target sequences of DNA millions of times over. The magic happens through repeated cycles , and here's the brilliant bit - the number of copies doubles each time, following the formula 2^n where n equals the number of cycles.
Each PCR cycle has three precise temperature steps. First, the DNA gets heated to 92-98°C, which breaks hydrogen bonds between base pairs and separates the double strands - imagine unzipping a zip.
Next, cooling to 50-65°C allows primers to bind to their target sequences on the separated strands. Finally, heating to 70-80°C lets the star of the show - heat-tolerant DNA polymerase - get to work replicating the target sequence.
Mind-Blowing Fact: After just 30 cycles, you'll have over a billion copies of your original DNA sequence!
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The Lagging Strand Challenge
Here's where DNA replication gets a bit tricky - not all strands can be copied the same way! The lagging strand faces a unique problem because DNA polymerase (the copying enzyme) can only add nucleotides in one specific direction.
Unlike its partner (the leading strand), the lagging strand cannot be replicated continuously. Instead, it gets copied in short chunks called fragments - think of it like writing backwards, one word at a time rather than flowing sentences.
The process requires several primers to be added at different points along the replication fork. DNA polymerase then builds each fragment separately, working in its preferred direction. Finally, the enzyme ligase acts like molecular glue, joining all the fragments together into one complete strand.
Memory Trick: Think "lagging = lagging behind = needs fragments" to remember this tricky process!
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Improve your grades
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What You Need for PCR
Think of PCR like a recipe - miss one ingredient and the whole thing fails! You need five essential components in your PCR tube: the target DNA sequence you want to copy, primers (short DNA fragments that kickstart the process), DNA nucleotides (the building blocks), enzymes to do the actual copying, and a pH buffer to keep conditions stable.
Scientists use control experiments to prove each component is necessary. For instance, if they want to show primers are essential, they'll run one tube with all ingredients except primers - and surprise, no DNA copies are made!
PCR has some pretty amazing real-world applications that you've probably seen on TV crime shows. It helps solve crimes by analysing tiny DNA samples, settles paternity disputes, and can diagnose genetic disorders before symptoms even appear.
Quick Tip: PCR is often paired with gel electrophoresis, which sorts DNA fragments by size using an electrical current - like a molecular sorting machine!
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Students love us — and so will you.
4.9/5
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4.8/5
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user