Teacher Resource 6: How are monoclonal antibodies used?



Teacher Resource 6How are monoclonal antibodies used?This activity walks learners through the stages of how monoclonal antibodies are used in pregnancy tests.A 'pregnancy test strip' is marked out on the floor of a corridor/playground and learners take on the roles of mobile and attached monoclonal antibodies and human chorionic gonadotrophin molecules. The teacher will talk learners through the stages along the pregnancy test strip.Learners then complete the worksheet to show their understanding.Teacher preparationA corridor is the perfect width to act as a pregnancy test stick and teachers will need to mark out three bands on the floor to act as the mobile antibiotic strip, test strip and check strip as shown below:UrineMobile Ab stripTest stripCheck stripPrint out the labels - mobile antibodies should be printed on blue card/paper and the rest on white paper. Give each learner their respective label as indicated below:20% of the learners will be immobilised (fixed) antibodies to hCG and will stand in the test strip touching the wall (as they are attached to the test strip).20% of learners will be immobilised antibodies to the mobile antibodies and will stand touching the wall as they are also attached to the check strip.40% of learners will be mobile antibodies to hCG and will stand in random positions within the mobile Ab strip.The remaining 20% of learners will be hCG molecules in the urine and will stand at the start of the pregnancy testing stick.InstructionsTeachers give learners instructions on what to do, explaining what is happening at each stage. Teachers walk along the 'stick' marking out the distance the urine has moved.When pregnant:The pregnancy test stick is dipped into urine. Urine containing human chorionic gonadotrophin (hCG) molecules move along the pregnancy test strip by capillary action.The urine reaches the mobile Ab strip, the antibodies in the strip have blue beads attached (hence the labels on blue card) and the shape of the binding sites on the antibody are specific to the hCG molecule. The hCG molecules therefore bind to some of the mobile antibodies forming an hCG-antibody complex. At this point hCG learners link arms with a mobile antibody.The urine continues to move along the pregnancy test stick taking the hCG-antibody complexes and the mobile antibodies that have no hCG bound with it to the Test strip.At the test strip, hCG-antibody complexes bind to the immobile antibodies as there binding sites are also specific to the hCG molecules. The pairs of learners playing the role of hCG-antibodies now link arms with the Immobile antibodies on the test strip and hold up their blue labels. They now cannot move any further as they are 'stuck' to the strip and the blue beads give the strip it's blue colour to show the woman is pregnant.The urine continues to move along the strip, now carrying only the mobile antibodies that did not bind to hCG molecules. Once these reach the check strip, they bind to the immobilised antibodies there, the beads giving that strip a blue colour also. The remaining mobile antibodies link arms with the immobile antibodies in this section and hold up their blue labels. This strip is used to check that the pregnancy test stick is actually working (to reduce false negatives).Not pregnant:The same as above, however learners holding the hCG labels sit out and do not take part. Only the mobile antibody, learners link arms with the immobile antibodies in the check strip as there are no hCG-antibody complexes made therefore no binding to immobile antibodies on the test strip.Images for learner labelsMobile antibodyhCG hormoneImmobile antibody (test strip)Immobile antibody (check strip)AnswersMobile antibodies (Abs)Test stripCheck stripattached to blue beadsimmobile Absimmobile Abs66167099695001. Urine 66167097155002. Urine 66230595250003. Urine The urine moves towards the end of the pregnancy test stick and any remaining mobile antibodies bind to the specific immobile antibodies on the check strip giving it a blue colour and proving the pregnancy test is working correctly.Explain how and why the results are different when the urine of a woman who is not pregnant is used.Only the check strip would go blue. This is because there will be no hCG hormone in the urine to bind to the mobile antibodies. Therefore as the mobile antibodies are carried along the pregnancy test stick, they will not bind to the immobile antibodies on the test strip because they are the wrong 'shape' for the binding sites on the immobile antibodies on this strip. They will however bind to the immobile antibodies on the check strip as they are specific to the binding sites on those antibodies. The blue beads therefore get 'stuck' here, proving that the pregnancy test stick is working correctly.Find out and explain how monoclonal antibodies can be used to detect cancers such as prostate cancer.The monoclonal antibodies are labelled with a radioactive element. They are then given to a patient via a drip and travel around the body in the blood. Once they come in to contact with a cancer cell covered with the complementary antigen, they bind to the antigen on its surface. Cameras are then used to detect any areas of radioactivity – bright spots show the presence of cancer cells (the monoclonal antibody acts as a marker).Explain why monoclonal antibodies that carry drugs improve the effectiveness of a treatment.They carry the drug directly to the cancer cell/tumour and they minimise damage to normal cells surrounding the tumour therefore reducing side effects. ................
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