Medical Interventions and Principles of Biomedical Science

Guided Notes

Antibodies and ELISA. Fill these in as we go, and label every diagram.

Date
Friday, September 18, 2026
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Diagrams
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These notes are the exam. Everything a question can be built from is on these pages, and the four diagrams are the four most likely places a question starts.

You turn in
  • Every blank filled.
  • All four diagrams labelled in your own hand.

Time: During the lecture.

Green ruleYou write here. Nothing else on the page is yours to fill in.
Gold groundGiven to you. Do not re-derive it. Controls and reference values live here.
Grey groundInstructions from Mr. Mendoza. Read before you start the step.
Red groundSafety. Read it before you touch any material.
SEC 01The twenty lines
Read this

Fill each blank as we reach it. Do not write ahead; the order is the argument.

The twenty lines ยท you complete these

1. A protein's ________________________ decides what it can bind to.

2. A protein's shape comes from the ________________________ which a gene specifies.

3. An antibody is shaped like a ________________________ and is built from four chains.

4. The two long chains are the ________________________ and they form both arms and the stem.

5. The two short chains are the ________________________ and they sit on the outside of the arms.

6. The arm tips are the ________________________ which differs between antibodies and carries the binding site.

7. The stem is the ________________________ which immune cells read to know what to do.

8. The chains are held together by ________________________ which are sulfur to sulfur links.

9. The small patch an antibody recognises is called an ________________________ and one germ carries many of them.

10. A B cell displays ________________________ receptor shape on its surface.

11. When an invader seats into a receptor, that cell divides. This is called ________________________ .

12. A ________________________ cell makes antibody now. A ________________________ cell waits for next time.

13. Memory cells are the reason a ________________________ works.

14. The fast, general branch of the immune system is ________________________ immunity.

15. The slower, specific branch that remembers is ________________________ immunity.

16. ELISA stands for ________________________ .

17. In an ELISA the step that makes the result mean anything is the ________________________ .

18. More target in the sample means more ________________________ in the well.

19. Colour is turned into a concentration using a ________________________ .

20. A screening test is tuned to miss almost nothing, so it accepts ________________________ that a confirmatory test clears.

SEC 02Diagram 1: The antibody
Read this

The antibody. Label: heavy chain, light chain, variable region, constant region, binding site, disulfide bond.

THE ANTIBODY, PART BY PARTSame colours on every diagram from here on. Learn them once.VARIABLE REGIONdifferent in every antibodythis is the part that recognisesBINDING SITEthe notch. Two per antibodyLIGHT CHAINtwo of them, the short onesHEAVY CHAINtwo of them, the long onesthey make both arms and the stemDISULFIDE BONDSsulfur to sulfur, holdingthe four chains togetherCONSTANT REGIONthe same in every antibodyof a class. This end talksto immune cellsTWO ENDS, TWO JOBS.The top finds the invader. The bottom tells the rest of the immune system what to do about it.That is why the top varies between antibodies and the bottom does not.
Label this diagram yourself. The printed labels are your check, not your answer; cover them and name the parts first.
You complete this

Write the sentence the task above asks for:

SEC 03Diagram 2: Binding
Read this

Binding. Label: epitope, variable region, and write one sentence on why the other three bumps do not bind here.

THE MOMENT OF BINDING, CLOSE UPTwo shapes meeting. No cutting, no killing, just holding on to one patch.ONE GERM CARRIES MANY DIFFERENT EPITOPES, and your body makes a different antibodyfor each one.VARIABLE REGIONthe notch is this shapeEPITOPEthe one patch it recognisesseats here
Label this diagram yourself. The printed labels are your check, not your answer; cover them and name the parts first.
You complete this

Write the sentence the task above asks for:

SEC 04Diagram 3: Making the right antibody
Read this

Making the right antibody. Label: B cell, antigen, plasma cell, memory cell. Then write what clonal selection means in one sentence.

HOW YOUR BODY MAKES THE RIGHT ANTIBODYIt does not design one to order. It already has millions, and the invader picks which one gets copied.1. MANY B CELLSeach with a different receptor2. ONE MATCHESthe antigen seats in one receptor3. THAT ONE DIVIDESonly the matching cell is copied4. TWO FATESplasma and memory cellsPMplasma cell: makesantibody nowmemory cell: waits for nexttimeTHIS IS WHY A VACCINE WORKS, AND WHY YOU USUALLY GET CHICKENPOX ONCE.The memory cells from step 4 are still there years later, so the second meeting is answered in days insteadof weeks.THE NAME FOR THIS: clonal selection. The invader selects which B cell gets cloned.Nothing designs the antibody. The right one already existed, and it got copied.
Label this diagram yourself. The printed labels are your check, not your answer; cover them and name the parts first.
You complete this

Write the sentence the task above asks for:

SEC 05Diagram 4: The ELISA
Read this

The ELISA. Label: capture antibody, target, detection antibody, enzyme, substrate. Then mark every place a wash happens.

HOW AN ELISA TURNS BINDING INTO A COLOUR YOU CAN MEASURERead left to right. The wash step between each one is the step that makes the result mean anything.1. COATCapture antibodies arestuck to the bottom ofthe well.2. ADD SAMPLEIf the target is in thesample, it seats into acapture antibody. ThenWASH.3. ADD DETECTORA second antibodycarrying an enzymebinds the other side.Then WASH.4. ADD SUBSTRATEThe enzyme changes thesubstrate and the wellturns colour.enzymeTHE WASH IS THE WHOLE TEST.Anything that did not specifically bind gets washed away. What is left is only what bound, so the colour at the endis a measure of how much target was in the sample. No wash, no meaning.WHAT AN ELISA IS USED FORDetecting an infection by finding either the germ's antigen or your antibodies against it. Screening donated blood.Allergy testing. Pregnancy tests. Any question shaped like: is this specific molecule here, and how much of it?
Label this diagram yourself. The printed labels are your check, not your answer; cover them and name the parts first.
You complete this

Write the sentence the task above asks for: