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- Title
Use of a laboratory exercise on molar absorptivity to promote student skepticism.
- Authors
Bailey, Cheryl; Madhavan, S.; Markwell, John
- Abstract
Skepticism, when promoted as a desirable trait amongst undergraduate students, can effect a marked increase in their cognitive development. We will describe a biochemistry laboratory exercise that can be utilized to promote student skepticism. The individual exercises in our laboratory course are made more relevant by providing a thematic thread, β-galactosidase, that links concepts in one exercise with those in latter exercises. The substrate for the continuous assay of β-galactosidase is the ehromogenic 2-nitrophenyl-β-D-galactopyranoside that produces 2-nitrophenol (2-NP). In one of the laboratory exercises, students prepare a series of ten differently buffered solutions by using KH2PO4 and K2HPO4, mixed with 50 µM 2-NP, to determine the wavelength of maximum absorption for the protonated and deprotonated form of each molecule. After determining the pH of the individual solution they determine the pKa value for 2-NP. The molar absorptivity of 2-NP is then determined, by preparing different dilutions of 5mM 2-NP in a solution of K2HPO4. The average molar absorptivity value for 2-NP determined by 38 students in one semester was 3560 ± 1060 at 420 nm, at a pH of 9.2. Students are encouraged to discuss that apparent discrepancies in the published molar absorptivity values for 2-NP (2150 to 21,300) at almost the same pH and at 420 nm with their own molar absorptivity values for 2-NP.
- Subjects
LABORATORIES; ABSORPTION; SKEPTICISM; STUDENTS; BIOCHEMISTRY
- Publication
FASEB Journal, 2007, Vol 21, Issue 5, pA299
- ISSN
0892-6638
- Publication type
Article
- DOI
10.1096/fasebj.21.5.a299-c