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21 Dec 2025

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3 pages

Understanding Proteins: Unit 2 Biology OCR

Emma Bell

@ebell1797

Proteins are absolutely everywhere in your body - from the... Show more

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Proteins and Amino Acids

Think of amino acids as biological LEGO blocks that snap together to create incredible structures. These 20 different building blocks combine to form polypeptides, which then fold into the complex proteins your body needs to function.

Every amino acid has the same basic structure: an amine group (the basic bit), a carboxylic acid group (the acidic bit), and a unique side chain $the R-group$ that gives each amino acid its personality. This dual nature makes them amphoteric - they can act as both acids and bases, which is pretty handy for biological processes.

Your body is constantly using proteins for different jobs. Structural proteins like collagen keep your tissues strong, enzymes speed up chemical reactions, and antibodies fight off infections. Transport proteins shuttle materials around, whilst hormone proteins carry messages between cells.

Quick Tip: Remember the "essential nine" - these are amino acids your body can't make, so you must get them from food. The other amino acids can be synthesised from what you eat.

Protein Storage and Structure

Here's something that might surprise you: your body cannot store protein like it stores fat or carbs. The amine groups become toxic in large amounts, so your liver removes excess amino acids through deamination, converting them to urea that you wee out.

Primary structure is simply the sequence of amino acids linked by peptide bonds - think of it as the protein's recipe. Change just one amino acid, and the entire protein might stop working properly. That's why genetic mutations can be so serious.

Secondary structure gets more interesting. Those peptide bonds create weak hydrogen bonds that twist the chain into recognisable shapes: the alpha-helix (like a spiral staircase) or beta-pleated sheets (like folded paper). These patterns give proteins their initial 3D form.

Remember: Heat denatures proteins by breaking the bonds that hold their shape - that's why egg whites go from clear to white when you cook them!

Advanced Protein Structure

Tertiary structure is where proteins get their final, complex 3D shape. The alpha-helixes fold even further using different types of bonds: strong disulphide bonds, ionic bonds (easily broken by pH changes), and numerous hydrogen bonds that can snap with heat.

Water plays a crucial role here through hydrophilic and hydrophobic interactions. The water-loving parts of amino acids face outward, whilst the water-hating parts cluster in the centre. This creates globular proteins that dissolve easily in your watery body fluids.

Finally, quaternary structure involves multiple polypeptide chains working together as a team. Haemoglobin is a perfect example - four protein chains plus an iron atom work together to carry oxygen around your body.

Key Insight: Protein folding isn't random - the amino acid sequence determines the final shape, and the shape determines the function. Get the folding wrong, and diseases like Alzheimer's can result.

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21 Dec 2025

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3 pages

Understanding Proteins: Unit 2 Biology OCR

Emma Bell

@ebell1797

Proteins are absolutely everywhere in your body - from the collagen in your skin to the enzymes breaking down your lunch. Understanding how these complex molecules are built from simple amino acid building blocks will help you grasp one of... Show more

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Proteins and Amino Acids

Quick Tip: Remember the "essential nine" - these are amino acids your body can't make, so you must get them from food. The other amino acids can be synthesised from what you eat.

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Protein Storage and Structure

Remember: Heat denatures proteins by breaking the bonds that hold their shape - that's why egg whites go from clear to white when you cook them!

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Advanced Protein Structure

Key Insight: Protein folding isn't random - the amino acid sequence determines the final shape, and the shape determines the function. Get the folding wrong, and diseases like Alzheimer's can result.