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3 Jan 2026

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3 pages

Understanding Antibodies - AQA A-Level Biology Notes

Amala Seth

@amala_seth

Your immune system has some pretty clever weapons to fight... Show more

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Monday 12th December 2022 Antibodies:

> What are antibodies?

proteins produced by B-lymphocytes, which have
specific binding sites designe

What Are Antibodies and How Do They Work?

Think of antibodies as your body's personal security team - they're proteins made by special white blood cells called B-lymphocytes. Each antibody is like a highly specialised bouncer that only recognises one specific troublemaker.

The structure is quite brilliant really. Antibodies have a quaternary protein structure made of four chains - two short "light chains" and two longer "heavy chains" all linked together. What makes them so effective is that each antibody has two identical binding sites that perfectly match a specific antigen, like a lock and key.

Here's where it gets interesting for fighting infections. When antibodies find their target bacteria, they cause agglutination - basically clumping the bad guys together. This makes it much easier for your immune system's cleanup crew (phagocytes) to find and destroy them.

Quick Tip: The variable region of antibodies changes between different types, whilst the constant region stays the same - this is why each antibody can target different threats whilst still being recognised by your immune system.

Memory Cells and Your Body's Learning System

Your immune system is incredibly smart - it actually remembers past infections through memory cells. These cells hang around in your body for years, just waiting quietly for their specific enemy to show up again.

When the same pathogen tries to attack you a second time, these memory cells spring into action and divide rapidly. This creates a rapid immune response that destroys the infection before you even feel ill - which is exactly how vaccines work to protect you.

Key Point: This is why you usually only get certain illnesses like chickenpox once - your memory cells remember and quickly eliminate the virus before symptoms develop.

Monoclonal Antibodies: Laboratory-Made Defenders

Monoclonal antibodies are basically identical copies of one specific antibody type, artificially produced in laboratories. Scientists identify the right B-lymphocyte, then make it divide through mitosis to create loads of identical antibodies.

These lab-made antibodies have some pretty amazing uses in medicine. For cancer treatment, they can be designed to target specific tumour markers, delivering drugs directly to cancer cells whilst leaving healthy cells alone.

You've probably encountered monoclonal antibodies without realising it. Pregnancy tests use antibodies that bind to the hormone hCG - if you're pregnant, the antibodies bind to the hormone and turn the test strip blue.

The ELISA test $enzyme-linked immunosorbent assay$ is another clever application used in medical diagnostics. It works by using antibodies to detect and measure specific proteins in samples. The process involves multiple steps of binding, washing, and adding enzymes that create coloured products - the stronger the colour, the more of the target protein is present.

Real-World Connection: ELISA tests are used for everything from detecting food allergies to monitoring hormone levels, making them one of the most versatile diagnostic tools in medicine.

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Biology

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3 Jan 2026

•

3 pages

Understanding Antibodies - AQA A-Level Biology Notes

Amala Seth

@amala_seth

Your immune system has some pretty clever weapons to fight off infections, and antibodies are among the most important. These protein molecules act like highly trained detectives, seeking out specific threats and marking them for destruction.

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What Are Antibodies and How Do They Work?

Quick Tip: The variable region of antibodies changes between different types, whilst the constant region stays the same - this is why each antibody can target different threats whilst still being recognised by your immune system.

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Memory Cells and Your Body's Learning System

Key Point: This is why you usually only get certain illnesses like chickenpox once - your memory cells remember and quickly eliminate the virus before symptoms develop.

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Monoclonal Antibodies: Laboratory-Made Defenders

Real-World Connection: ELISA tests are used for everything from detecting food allergies to monitoring hormone levels, making them one of the most versatile diagnostic tools in medicine.