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Updated 20 Feb 2026
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Proteins and Their Functions - AQA A Level Biology Guide
T
thomas
@thomasrg04
Protein Structure and Formation
Think of proteins as incredibly sophisticated LEGO structures - they start with simple building blocks called amino acids and end up as complex 3D masterpieces that keep you alive!
There are 20 essential amino acids, and they're like identical twins except for one key difference: their R group (side chain). This R group is what gives each amino acid its unique personality and determines how the final protein will behave.
When two amino acids join together through a condensation reaction, they form a peptide bond and release a water molecule. Two amino acids make a dipeptide, whilst many amino acids create a polypeptide chain. It's like building a chain where each link has its own special properties.
Proteins have four levels of structure that work together like a perfectly choreographed dance:
- Primary structure: The basic sequence of amino acids held together by peptide bonds - think of it as the protein's DNA code
- Secondary structure: Hydrogen bonds cause the chain to fold into repeating patterns like alpha helices or beta pleated sheets
- Tertiary structure: The complex 3D shape formed when the secondary structures twist and fold, held together by hydrogen bonds, ionic bonds, Van der Waals forces, and disulfide bridges
- Quaternary structure: Multiple polypeptide chains working together, sometimes with added prosthetic groups
Quick Test Tip: The Biuret test detects proteins by turning from blue to purple when peptide bonds are present. Grind your sample, add Biuret solution , and watch for the colour change!
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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.
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Anna
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Best app on earth! no words because it’s too good
Thomas R
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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.
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Greenlight Bonnie
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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.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
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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
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Proteins and Their Functions - AQA A Level Biology Guide
T
thomas
@thomasrg04
Proteins are absolutely everywhere in your body - from the muscles that help you move to the enzymes that digest your food. Understanding how these complex biomolecules are built from simple amino acid building blocks is crucial for your A-Level... Show more
Protein Structure and Formation
Think of proteins as incredibly sophisticated LEGO structures - they start with simple building blocks called amino acids and end up as complex 3D masterpieces that keep you alive!
There are 20 essential amino acids, and they're like identical twins except for one key difference: their R group (side chain). This R group is what gives each amino acid its unique personality and determines how the final protein will behave.
When two amino acids join together through a condensation reaction, they form a peptide bond and release a water molecule. Two amino acids make a dipeptide, whilst many amino acids create a polypeptide chain. It's like building a chain where each link has its own special properties.
Proteins have four levels of structure that work together like a perfectly choreographed dance:
- Primary structure: The basic sequence of amino acids held together by peptide bonds - think of it as the protein's DNA code
- Secondary structure: Hydrogen bonds cause the chain to fold into repeating patterns like alpha helices or beta pleated sheets
- Tertiary structure: The complex 3D shape formed when the secondary structures twist and fold, held together by hydrogen bonds, ionic bonds, Van der Waals forces, and disulfide bridges
- Quaternary structure: Multiple polypeptide chains working together, sometimes with added prosthetic groups
Quick Test Tip: The Biuret test detects proteins by turning from blue to purple when peptide bonds are present. Grind your sample, add Biuret solution , and watch for the colour change!
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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.
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Sudenaz Ocak
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Greenlight Bonnie
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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.
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 Knowunity AI. 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 Knowunity AI. 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