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18
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L
Lucinda Williams
29/08/2025
Biology
DNA - GCSE Edexel Combined science Biology
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29 Aug 2025
•
DNA Extraction and Structure for GCSE Edexcel Combined Science
L
Lucinda Williams
@lucindawilliams_tzaw
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DNA Structure and Components
DNA (Deoxyribonucleic Acid) is a complex molecule that carries genetic information. Understanding its structure is crucial for GCSE Biology and Edexcel Combined Science students.
DNA Composition:
- DNA strands are polymers made up of repeating units called nucleotides.
- Each nucleotide consists of a sugar molecule, a phosphate molecule, and a base.
- The sugar and phosphate molecules form the 'sugar-phosphate backbone' of the DNA strands, alternating along the length.
- One of four bases attaches to each sugar: Adenine (A), Thymine (T), Cytosine (C), or Guanine (G).
Vocabulary: Nucleotide - The basic structural unit of DNA, consisting of a sugar, a phosphate, and a nitrogenous base.
DNA Structure: 5. A DNA molecule has two strands coiled together in the shape of a double helix. 6. Each base on one strand links to a complementary base on the opposite strand. 7. Complementary base pairing occurs: A always pairs with T, and C always pairs with G. 8. The complementary base pairs are joined together by weak hydrogen bonds.
Highlight: Complementary base pairing in DNA GCSE biology is a crucial concept. Remember: A-T and C-G are the only allowed pairings.
Chromosomes and Genes:
- Chromosomes are long, coiled-up molecules of DNA found in the nucleus of eukaryotic cells.
- A gene is a section of DNA on a chromosome that codes for a particular protein. The sequence of bases in the gene determines the protein produced.
- All of an organism's DNA makes up its genome.
Definition: Genome - The complete set of genetic material in an organism.
DNA Extraction Practical:
This section outlines a method for DNA extraction from fruit cells, specifically strawberries, which is a common GCSE Biology experiment.
Materials needed:
- Strawberries
- Detergent
- Salt
- Ice-cold ethanol
- Beaker
- Filter
- Glass rod
Procedure:
-
Mash strawberries and place them in a beaker containing a solution of detergent and salt. Mix well.
Example: The detergent breaks down cell membranes to release the DNA, while the salt helps the DNA stick together.
-
Filter the mixture to remove froth and large insoluble cell parts.
-
Gently add ice-cold ethanol to the filtered mixture.
Highlight: Why is ice cold ethanol used in DNA extraction? Cold ethanol causes DNA to precipitate out of solution, making it visible.
-
Observe the DNA precipitating as a stringy, white solid. It can be carefully removed using a glass rod.
Vocabulary: Precipitate - A solid that forms and separates from a solution.
This practical demonstration of DNA extraction GCSE Biology helps students visualize the normally invisible genetic material and understand the principles behind isolating DNA from cells.
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DNA Extraction and Structure for GCSE Edexcel Combined Science
L
Lucinda Williams
@lucindawilliams_tzaw
DNA Structure and Extraction: A Comprehensive Guide for GCSE Biology
This guide covers the structure of DNA, its components, and a practical method for DNA extraction from fruit cells. It's essential knowledge for GCSE Biology and Edexcel Combined Science... Show more
DNA Structure and Components
DNA (Deoxyribonucleic Acid) is a complex molecule that carries genetic information. Understanding its structure is crucial for GCSE Biology and Edexcel Combined Science students.
DNA Composition:
- DNA strands are polymers made up of repeating units called nucleotides.
- Each nucleotide consists of a sugar molecule, a phosphate molecule, and a base.
- The sugar and phosphate molecules form the 'sugar-phosphate backbone' of the DNA strands, alternating along the length.
- One of four bases attaches to each sugar: Adenine (A), Thymine (T), Cytosine (C), or Guanine (G).
Vocabulary: Nucleotide - The basic structural unit of DNA, consisting of a sugar, a phosphate, and a nitrogenous base.
DNA Structure: 5. A DNA molecule has two strands coiled together in the shape of a double helix. 6. Each base on one strand links to a complementary base on the opposite strand. 7. Complementary base pairing occurs: A always pairs with T, and C always pairs with G. 8. The complementary base pairs are joined together by weak hydrogen bonds.
Highlight: Complementary base pairing in DNA GCSE biology is a crucial concept. Remember: A-T and C-G are the only allowed pairings.
Chromosomes and Genes:
- Chromosomes are long, coiled-up molecules of DNA found in the nucleus of eukaryotic cells.
- A gene is a section of DNA on a chromosome that codes for a particular protein. The sequence of bases in the gene determines the protein produced.
- All of an organism's DNA makes up its genome.
Definition: Genome - The complete set of genetic material in an organism.
DNA Extraction Practical:
This section outlines a method for DNA extraction from fruit cells, specifically strawberries, which is a common GCSE Biology experiment.
Materials needed:
- Strawberries
- Detergent
- Salt
- Ice-cold ethanol
- Beaker
- Filter
- Glass rod
Procedure:
-
Mash strawberries and place them in a beaker containing a solution of detergent and salt. Mix well.
Example: The detergent breaks down cell membranes to release the DNA, while the salt helps the DNA stick together.
-
Filter the mixture to remove froth and large insoluble cell parts.
-
Gently add ice-cold ethanol to the filtered mixture.
Highlight: Why is ice cold ethanol used in DNA extraction? Cold ethanol causes DNA to precipitate out of solution, making it visible.
-
Observe the DNA precipitating as a stringy, white solid. It can be carefully removed using a glass rod.
Vocabulary: Precipitate - A solid that forms and separates from a solution.
This practical demonstration of DNA extraction GCSE Biology helps students visualize the normally invisible genetic material and understand the principles behind isolating DNA from cells.
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
Where can I download the Knowunity app?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
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Stefan S
iOS user
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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
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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.
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Anna
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Thomas R
iOS user
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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.
David K
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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