AQA GCSE Biology Revision
How Monoclonal Antibodies and Fluorescent Dye Identify Molecules
Learn why monoclonal antibodies can be used as specific markers in research and diagnostic testing.
Exam answer
The short version
A monoclonal antibody is made to bind to one specific molecule or antigen. A fluorescent dye can be attached to the antibody, so when the antibody binds to its target, the molecule can be located or identified because the dye shows where binding has happened.
Before the example
The antibody gives specificity; the dye gives visibility
The antibody and dye do different jobs. The monoclonal antibody recognises and binds to a specific target. The fluorescent dye makes the binding visible, so researchers can see where the target molecule is in a sample.
Why monoclonal antibodies are useful
Monoclonal antibodies are all identical and bind to the same specific target. This makes them useful when researchers need to find one particular molecule among many others in a cell, tissue sample or test sample.
Why fluorescent dye is attached
The dye does not make the antibody more specific. It acts as a marker. When the antibody attaches to the target molecule, the dye can be detected under suitable light or equipment, showing where the target molecule is present.
How to explain it in an exam
A strong answer separates the two roles clearly: the antibody binds specifically to the target molecule, and the fluorescent dye allows the bound antibody to be seen. Avoid saying the dye identifies the molecule by itself.
How it works
Use the antibody-and-marker sequence
- 1Produce or choose a monoclonal antibody that binds to the target molecule.
- 2Attach a fluorescent dye to the antibody.
- 3Add the labelled antibody to the sample.
- 4The antibody binds only where the target molecule is present.
- 5Detect the fluorescence to locate or identify the target molecule.
Key terms
Words to use in your answer
monoclonal
antibodies
Exam focus
This is often tested as an application question. The mark is usually for explaining both specificity and visibility: the antibody targets the molecule, and the fluorescent dye shows where it is.
Quick check
Can you answer these?
- What does the monoclonal antibody bind to?
- What is the role of the fluorescent dye?
- Why is specificity important in this method?
- Why should you not say the dye binds to the molecule by itself?
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