A Simple Classroom Teaching Technique To Help Students Understand Michaelis-Menten Kinetics

Abstract

A new, simple classroom technique helps cell biology students understand principles of Michaelis-Menten enzyme kinetics. A student mimics the enzyme and the student's hand represents the enzyme's active site. The catalytic event is the transfer of marbles (substrate molecules) by hand from one plastic container to another. As predicted, increases in marble concentration increase the number of marbles transferred per unit time (initial rate, V 0 ) until the turnover number becomes rate limiting and V 0 approaches the maximum velocity (V max ), as described by the Michaelis-Menten equation. With this demonstration, students visualize an important concept: the turnover number is constant and independent of marble concentration. A student assessment of this exercise showed that it helped students visualize the turnover number and V max but not K m , the marble concentration at which V 0 is one-half V max . To address the concept of K m , we use supplemental laboratory and lecture exercises. This exercise with plastic containers and marbles is equally suited to demonstrate the kinetics of carrier-mediated membrane transport. We conclude that this exercise helps students visualize the turnover number and V max and gives students important insights into the kinetic parameters used to characterize the catalytic activity of enzymes and membrane transporters.

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“…After teaching the class on the basic concepts concerning enzymes and enzyme kinetics, the Michaelis-Menten equation was introduced. The following points were clarified with the example of a marble experiment described by Runge et al 16 : physical meanings of K m and V max , turnover number, and obtaining K m and V max values using a reciprocal plot. In the marble experiment, 2 plastic containers (1 and 2) are used.…”

“…One of the important concepts that was clarified by the marble experiment was why, at higher concentrations of substrate, an enzyme reaches saturation. After demonstrating the marble experiment, 16 students identified that if the number of enzymes remains constant and, the substrate concentration is high, the velocity of the reaction must asymptotically approach a maximum. Sets of enzymes with different turnover numbers and K m values were provided to students in the classroom, with opportunities for them to apply their knowledge of K m values and turnover numbers to solidify their understanding.…”

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“…Teacher teams in this study were asked to repeat the method previously published by Runge et al (19), but without use of the blindfold, to assess if the collected kinetic data were hyperbolic. Teams (after being given sufficient time to complete their data collection and analysis) were surveyed in open discussion.…”

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