Physioex Answers

Positive and Negative Controls 1. Why are there a number of washing steps in serological tests? The are a number of steps needed in order to remove any non specific binding that may have occurred. 2. Describe how you would know that you had a “false positive” result. What does this mean for the rest of your results? A positive result with a negative control indicates a “false positive” and your results are invalidated.

3. Describe how you would know that you had a “false negative” result.What does this mean for the rest of your results? A negative results with a positive control indicates a “false negative” and your results are invalidated. Direct Fluorescent Antibody Technique 4. Why is this technique a direct method? It is considered a direct method because it involves conjugation of an antibody with fluorescent dye. 5. What is an elementary body? An elementary body is an infectious particle of any of several microorganisms.

6. How do elementary bodies look under the fluorescent microscope?Elementary bodies look red, no defined & varied shape with a darker spot on them and some had green spots or blotches on them. 7. What do you think would happen if you did not fix the sample to the slide with 95% ethyl alcohol? Since ethyl alcohol’s function is to fix the specimen to the slide, I would say the specimen would be washed away during the preparation of the slide if ethyl alcohol was not used. 8. Which patient(s) tested positive for Chlamydia? Patient 2& patient 4 9. Was there any nonspecific binding for any of the samples?Explain.

Patient 3 had just a tiny bit of green on it which made me think there was nonspecific binding because there were only two so its not negative or positive but in my opinion human error. Ouchterlony Technique 10. What is a precipitin line? A precipitin line is an insoluble precipitate formed when an antigen and antibody are cross linked. 11. What is the unknown antigen in the simulation? Since there is no reading or text for this activity I don’t understand how I am suppose to figure out what the unknown antigen is. 12.Considering your results, do you think that human serum albumin and bovine serum albumin have epitopes in common? Explain.

I would say they have similar or partial epitopes in common but not exact. 13. What is the process resulting in antigen and antibody moving toward each other? One dimensional diffusion Enzyme-Linked Immunosorbent Assay 14. In the “sandwich” analogy of the direct ELISA, what is the “bread”? Antibodies What is the filling? Antigens 15. Describe some advantages of using the ELISA technique to process a large number of samples.The advantage of Sandwich ELISA is that the sample does not have to be purified before analysis, and the assay can be very sensitive. 16.

Which patient(s) were positive for HIV? Patient C is HIV positive 17. Describe what would happen if you skipped the step where the developing buffer was added. The developing buffer contains the secondary antibodies that the enzyme is conjugated with and without that it wouldn’t develop right and the results would be inconclusive or “retest”Western Blotting Technique 18. The Western blot technique is used as the confirmatory test for a positive ELISA result because it provides better specificity. How does this technique provide better specificity? The Western blot provides better specificity because it detects antibodies binding to specific proteins and glycoproteins from HIV in the form of bands. 19. If a patient tests positive for HIV using the ELISA test but negative using Western blotting, what can you say about the initial ELISA result?

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