1.10: Competitive Binding Assays

1. The equation Ab + L \(\leftrightarrow\) AbL has which one of the following mathematical relationships?:
   1. $$K_{a} = \frac{[L] [AbL]}{[AbL]}$$
   2. $$K_{a} = \frac{[Ab] [AbL]}{[L]}$$
   3. $$K_{a} = \frac{[Ab] [L]}{[Ab] [AbL]}$$
   4. $$K_{a} = \frac{[AbL]}{[Ab] [K]}$$
   5. $$K_{a} = \frac{[Ab] [L]}{[L] [AbL]}$$
2. The binding constant K_a for most saturation or competitive type reactions is on
   the order of:
   1. K_a = 10⁺¹ L/mol
   2. K_a = 10⁺³ L/mol
   3. K_a = 10⁺⁵ L/mol
   4. K_a = 10⁺⁹ L/mol
   5. K_a = 10⁺¹⁵ L/mol
3. Indicators (labels) for competitive reactions do not include which one of the
   following?:
   1. fluorescent dyes
   2. enzymes
   3. hormones
   4. radioisotopes
   5. fluorescent labels
4. For a good competitive binding assay, the proportion of antibody to labeled ligand should be:
   1. more Ab than labeled ligand
   2. in the same molar ratio
   3. less Ab than labeled ligand
   4. greater in free ligand
   5. less in free ligand
5. In order to determine the amount bound and unbound in a radioisotope competitive assay, what is necessary?
   1. the two forms must be separated from each other
   2. the two forms must be derivatized
   3. the two forms must be analyzed by different counters
   4. a high specific activity must be chosen
   5. the ratio must be determined in the same assay tube
6. Which of the following compounds are not often monitored by competitive binding assays?
   1. therapeutic drugs
   2. protein hormones
   3. estrogens
   4. antibiotics
   5. electrolytes
7. Given that at equilibrium a solution contains 1 x 10^-7 M unbound antibody, 1 x 10^-6 M unbound ligand, and 1 x 10^-7 M bound antibody, what is the approximate association constant K_a?
   1. 10⁵
   2. 10⁶
   3. 10⁷
   4. 10⁸
   5. 10¹³
8. What is the function of the radioisotope in a competitive binding assay?:
   1. to affect the equilibrium
   2. to make the ligand bind better
   3. to make the antibody bind
   4. to determine the amount of free or bound material
   5. to determine the effect on the antibody binding curve
9. One limiting physical property of a competitive binding assay is the _____________ of antigen and antibody:
   1. affinity constant
   2. acidity constant
   3. alkaline constant
   4. radioactivity constant
   5. enzyme constant
10. In the competitive binding assays which of the following is/are kept constant?:
    1. ligand
    2. labeled ligand
    3. antibody (total)
    4. ligand and antibody (total)
    5. labeled ligand and antibody (total)
11. What type of relationship exists between % of labeled ligand bound and concentration of added ligand in a competitive binding displacement reaction?:
    1. linear
    2. logarithmic
    3. non linear
    4. variable dose response
    5. non-variable dose response
12. Radioisotopes are used in competitive binding assays to label ligands. They require one step in the procedure that:
    1. separates antibody and labeled ligand
    2. separates labeled ligand from unlabeled ligand
    3. separates labeled antibody from unlabeled ligand
    4. separates antibody-bound ligand from free ligand
    5. separates unbound antibody from ligand
13. If an antibody has an association constant of 108 M then what is the most likely limit of sensitivity of an immunoassay using it as reagent?:
    1. 10^-4 M
    2. 10^-6 M
    3. 10^-8 M
    4. 10^-10 M
    5. 10^-16 M
14. Competitive binding reactions are (best answer/answers):
    1. reversible
    2. non-reversible
    3. involve a binding protein and a ligand
    4. (a) and (c)
    5. (b) and (c)
15. Characteristics of competitive binding reactions include:
    1. specificity
    2. affinity
    3. typically involves the binding of large molecules to binding proteins
    4. use only antibodies as binding proteins
16. To generate antibodies to small molecules, it is necessary for the latter to be:
    1. aromatic
    2. contain long aliphatic chains
    3. greater than a 1000 dalton molecular weight
    4. coupled to large macromolecules
17. A competitive binding reaction is described by which equation:
    1. Ligand + Binding Protein \(\leftrightarrow\) Ligand:Binding Protein Complex
    2. Ligand + Labeled Ligand \(\leftrightarrow\) Ligand:Labeled Ligand Complex
    3. Ligand + Labeled Ligand + Binding Protein \(\leftrightarrow\) Ligand:Binding Protein Complex + Labeled Ligand:Binding Protein Complex + Ligand + Labeled Ligand
    4. Labeled Ligand + Binding Protein \(\leftrightarrow\) Labeled Ligand: Binding Protein Complex
18. As the concentration of ligand increases in a competitive binding reaction, the amount of labeled ligand bound to the binding protein:
    1. increases
    2. decreases
    3. stays the same
19. Heterogeneous competitive binding formats require that:
    1. the binding protein modulates the activity of the label
    2. the bound labeled ligand be physically separated from the free, labeled ligand
    3. a radioactive element is used as the label
    4. none of the above
20. Labels for homogeneous assay formats include enzymes, radioisotopes, and substrates
    1. True
    2. False
21. Cross-reactivity is when molecules that are structurally similar to the ligand competitively bind to the binding protein
    1. True
    2. False
22. The dose response curve for a competitive binding assay (best answer):
    1. increases when measuring the free (unbound) labeled ligand
    2. decreases when measuring the bound labeled ligand
    3. decreases when measuring the free (unbound) labeled ligand
    4. increases when measuring the bound labeled ligand
    5. (a) and (b)
    6. (c) and (d)
23. CEDIA and EMIT are examples of:
    1. heterogeneous competitive binding assays
    2. homogeneous competitive binding assays competitive
    3. immunometric assay
    4. fluroimmunoassay
    5. point-of-care testing methods

Answer

1. d (p. 248)
2. d (p. 248)
3. c (p. 250)
4. b (p. 148)
5. a (p. 249,250)
6. e (p. 247)
7. b (p. 248)
8. d (p. 249, 250)
9. a (p. 248, 252)
10. e (p. 248, 254)
11. c (p. 248)
12. d (p. 249, 250)
13. c (p. 248, 251)
14. d (p. 247)
15. a (p. 247, 248., 250)
16. d (p. 247)
17. c (p. 248)
18. b (p. 248)
19. b (p. 249)
20. b (p. 249-251)
21. a (p. 252-253)
22. e (p.248)
23. b (p. 259)