How It Works: Antibodies as a Lock-and-Key System
Part of Adaptive Immunity and Antibodies — GCSE Biology
This how it works covers How It Works: Antibodies as a Lock-and-Key System within Adaptive Immunity and Antibodies for GCSE Biology. Specific immune responses, antibody production, lymphocytes, memory cells It is section 7 of 15 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
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Section 7 of 15
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20 questions
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How It Works: Antibodies as a Lock-and-Key System
The specificity of the adaptive immune response depends on a molecular lock-and-key relationship between antigens and antibodies. Every pathogen has unique surface molecules called antigens — typically proteins on the pathogen's outer surface. Each antigen has a specific three-dimensional shape.
B lymphocytes each carry a unique surface receptor complementary in shape to one specific antigen. When the matching antigen binds to a B cell's receptor, it is like a key fitting into a lock — only the B cell with the right receptor shape will respond. This is clonal selection: out of the many B cells with different receptor shapes, only the one(s) complementary to the invading pathogen's antigen are selected and activated.
Once activated, the B cell divides rapidly (clonal expansion) to produce a large group of identical cells. Most become plasma cells, which are essentially antibody factories — each can secrete thousands of antibody molecules per second. These antibodies flood into the blood and bind to antigens on the pathogen, tagging them for destruction by phagocytes or preventing them from attaching to host cells.
Crucially, some activated B cells become long-lived memory B cells. These persist in the body for years or decades. On second exposure to the same antigen, memory B cells respond within 1–3 days rather than the 5–10 days of the primary response, producing far more antibodies. This is why you are immune to diseases you have had before, and why vaccines work — they create memory cells without the risk of the actual disease.