GCSE · Biology · AQA · Spec 8461

Uses of monoclonal antibodies (HT, biology only)

A pregnancy test, a disease test, a map of cancer cells and a cancer treatment: four very different jobs, one identical trick.

Higher

Biology · Monoclonal antibodies

Detect, locate or treat?

Sort each card by what it's doing. Ask yourself: is it telling us whether something is there, showing where it is, or acting on the cells it binds to?

Still to sort

Detect a molecule in a sample (0)

Gives a yes-or-no answer: is the target in this sample?

Where the line is: Detecting asks 'is it in this sample?'. Locating asks 'where is it in the cells and tissues?'.

Locate molecules in cells and tissues (0)

Shows where the target is.

Where the line is: Locating uses a fluorescent dye that only shows. Treating needs an attachment that acts on the cell.

Treat a disease (0)

Delivers something that acts on the cells the antibody binds to.

Where the line is: Treating carries a radioactive substance or a toxic drug. A dye on the same antibody would only show where the cells are.

5 of 5 still to sort.

Every card uses a monoclonal antibody: an antibody that binds to just one target, because its shape is complementary to that target, like a key that fits one lock. What changes from card to card is what the antibody is attached to.

Exam line: To explain any use, name two things: the one molecule the antibody binds to, and what the antibody is attached to.
Watch out: Same target doesn't mean same job. Look at the two cards that bind the same tumour-cell antigen: one locates, one treats. The attachment made the difference.
UK note

AQA GCSE Biology 8461, section 4.3.2.2: Higher tier only, and biology only (not part of Combined Science).

Higher

Inside a pregnancy test

Step through it. Which stage is the antibody's shape doing the real work?

  1. HCG is madeWhen a woman is pregnant, her body produces a hormone called HCG.
  2. HCG gets into urineHCG is found in her urine. That's why urine is the sample the test uses.
  3. Urine meets the stripThe test strip has monoclonal antibodies attached to it, and every one of them is specific to HCG.
Higher

Reading a test strip

Two lines, two questions

Walk each route. Which line do you have to check first?

Has the test worked? → What does the result line show?

3 ways a two-line strip can be read.

On You look at the finished strip. 2 branches to choose from.

Test strips often show two lines. One tells you whether the test has worked. The other tells you whether the result is positive or negative. Read them in the right order.

Watch out: Don't read the result line on its own. If the 'test worked' line is missing, a result that looks negative could just be a test that failed.
Higher

Treating cancer

What does the antibody actually do?

Monoclonal antibodies are made against an antigen that a patient's tumour cells have and their healthy cells don't. A toxic drug is attached to the antibodies, and they are injected into the body.

Which is closest to what you think happens?
How sure are you?
Higher

Evaluate

The magic bullet: hit or miss?

The claim

Monoclonal antibodies have turned out to be the 'magic bullet' for cancer treatment that people hoped for.

Place each piece of evidence to load the balance. Mark the strong ones — they count double.

  1. They deliver a radioactive substance or a toxic drug to tumour cells rather than to other body cells.

    Evidence 1: does it support or challenge the claim?

  2. Traditional cancer treatments also affect healthy cells that divide rapidly, such as hair follicle cells.

    Evidence 2: does it support or challenge the claim?

  3. The same specific binding is already used in pregnancy tests, in diagnosing disease and in locating cancer cells and blood clots.

    Evidence 3: does it support or challenge the claim?

  4. Monoclonal antibody treatments have caused more side effects than expected.

    Evidence 4: does it support or challenge the claim?

  5. They come from the immune system of another organism, such as a mouse, so people's bodies sometimes reject them.

    Evidence 5: does it support or challenge the claim?

  6. Producing monoclonal antibodies uses living animals such as mice.

    Evidence 6: does it support or challenge the claim?

Exam line: An evaluation needs both sides and then a judgement. 'Not yet widely used' is a judgement you can back with evidence from both sides.

Higher

Your turn

Carry the idea to a new test

A test strip is used to find out whether a person is infected with one particular pathogen. A sample of the person's blood is put on the strip. Explain how the strip can show that this pathogen is present. [3 marks]

0 words · your answer stays on this page and is not sent anywhere.

Exam line: Explaining means saying why each step happens. Name the target, say why the antibody binds to it, then say what that binding shows.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Pregnancy tests, disease tests, finding cancer cells, treating tumours: work out how one trick does all four, and why it still isn't the 'magic bullet' people hoped for.

What you need to know

  • Monoclonal antibodies are identical antibodies made by a single clone of cells (hybridoma cells). Each one is specific to one target, such as one antigen or one other molecule.
  • They bind to their target because they are complementary in shape to it, and they bind only to that target.
  • That one property gives their uses: tests that detect specific molecules (for diagnosis and in laboratory testing), locating molecules in cells and tissues, and treating some diseases such as cancer.
  • They were hoped to be a 'magic bullet' for cancer, but they have caused more side effects than expected, the body sometimes rejects them, and making them uses animals.

The big picture

Monoclonal antibodies each bind to one specific target, because their shape is complementary to it. Attached to a test strip, they detect a molecule such as HCG or a pathogen's antigen. Labelled with a fluorescent dye, they locate cancer cells or blood clots. Carrying a radioactive substance or a toxic drug, they deliver treatment to tumour cells. They were hoped to be a 'magic bullet', but more side effects than expected, rejection and the use of animals mean they are not yet widely used.

Key points

1Pregnancy tests: HCG from the urine binds to HCG-specific antibodies on the strip, causing a colour change that shows a positive result.
2Two-line strips: one line shows the test has worked and the other shows positive or negative, which helps prevent incorrect results.
3Diagnosis: antibodies on a strip bind to the antigen of a specific pathogen in blood or saliva, so a positive result shows that pathogen is present.
4Locating: antibodies labelled with a fluorescent dye bind to their target, and the dye shows where cancer cells or blood clots are.
5Treating cancer: antibodies made against antigens that tumour cells have (and healthy cells don't) carry a radioactive substance, which helps reduce the tumour's size, or a toxic drug, which stops the tumour cells dividing.
6Limits: more side effects than expected (so not yet widely used), sometimes rejected because they come from another organism such as a mouse, and their benefits must be weighed against the use of animals.

Worked example

Problem

A doctor wants to find out where a blood clot is in a patient. Explain how monoclonal antibodies could be used to do this.

⚠ Watch out

Saying an antibody is 'specific to pregnancy' or 'specific to cancer'. An antibody is specific to one molecule: HCG, or one antigen on a tumour cell or a pathogen. Always name the molecule it binds to.

🧠

Memory hook

Find, then flag or fight. The antibody finds its one target; a test strip or a dye flags it; a toxic drug or a radioactive substance fights it.

✓

Check yourself

Cover the page. For a pregnancy test, a disease test, finding cancer cells and treating cancer, say what the antibody binds to and what it carries.

Flashcards

(12)
What are monoclonal antibodies?
Identical antibodies made by a single clone of cells. Each is specific to one target, such as one antigen.
Why does a monoclonal antibody bind to only one target?
Its shape is complementary to that target, so nothing else fits.
What are monoclonal antibodies used for?
Tests to detect specific molecules (diagnosis and laboratory testing), locating molecules in cells and tissues, and treating some diseases such as cancer.
How does a pregnancy test strip show a positive result?
Pregnant women produce HCG, found in urine. HCG binds to HCG-specific antibodies on the strip, causing a colour change.
Why do test strips often show two lines?
One shows the test has worked; the other shows positive or negative. This helps prevent incorrect results.
How can monoclonal antibodies show that a pathogen is present?
Antibodies on a strip bind to the antigen of that specific pathogen in a sample such as blood or saliva, giving a positive result.
How are monoclonal antibodies used to locate molecules in cells and tissues?
They are labelled with a fluorescent dye. Where they bind, the dye shows where cells carrying the target are, such as cancer cells or blood clots.
Why do cancer-treating monoclonal antibodies bind to tumour cells?
Tumour cells can have antigens that healthy cells don't, and the antibodies are made against those antigens.
What can be attached to monoclonal antibodies to treat cancer?
A radioactive substance, which helps reduce the size of the tumour, or a toxic drug, which stops the tumour cells dividing.
Why were monoclonal antibodies thought to be a 'magic bullet'?
They would deliver treatment to tumour cells, not healthy cells, causing less damage than traditional treatments, which also affect rapidly dividing healthy cells such as hair follicle cells.
Give two problems with monoclonal antibody treatments.
They have caused more side effects than expected (so they're not yet widely used), and the body sometimes rejects them because they come from another organism, such as a mouse.
What is the ethical issue with monoclonal antibodies?
Producing them uses living animals such as mice, so their benefits must be weighed against the use of the animals.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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