TEACHERS TOPICS Teaching Glycolysis with the Student s Perspective in Mind

TEACHERS TOPICS Teaching Glycolysis with the Student s Perspective in Mind Reza Karimi, PhD School of Pharmacy, Lake Erie College of Osteopathic Medicine Submitted January 30, 2005; accepted April 4, 2005; published December 1, 2005. This paper discusses the importance of considering the student s perspective when teaching, especially when presenting a complex subject such as glycolysis. One of the key elements in facilitating students understanding and learning of the material is providing illustrations and practical examples of the subject matter. The need for the introduction and integration of topics relating to glycolysis, including thermodynamics and enzymology, is emphasized. Keywords: student learning, thermodynamics, enzymology, glycolysis INTRODUCTION Teaching and learning are complex processes that are not mutually exclusive. The variation among students backgrounds as well as the difference between teachers in terms of how they conceptualize their duties and responsibilities add to the complexity of teaching and learning. As instructors, we have accepted that each student is unique in his or her learning techniques. In addition, we have learned that the extent of what we understand, for instance from studying a textbook, is greater than the level of what our students understand. On the other hand, students enjoy learning more when given illustrations that make the subject matter easier to comprehend. Simply put, students and teachers alike learn facts and concepts better when there is an illustration or model. No doubt, finding an illustration and model of what students need to learn is a demanding job that goes beyond studying and presenting the material to students from a textbook. Like any other job, while goals and objectives are the main points to direct the teaching procedures, enthusiasm and carefully planned presentations are the key points in effective teaching. Not only is it important to focus on what the students should learn, but how we should teach and deliver different topics to the students. The creativity of the teachers to find and employ new ideas plays a critical role in increasing students learning. As teachers, no matter how old or young, experienced or inexperienced, junior or senior we are, the one thing that we have in common is that we have been students, too. It will not take any significant time or effort from us, Corresponding Author: Reza Karimi, PhD. Address: Lake Erie College of Osteopathic Medicine, School of Pharmacy, Department of Pharmaceutical Sciences, 1858 West Grandview Boulevard, Erie, PA 16509. Tel: 814-866-8459. Fax: 814-866-8450. E-mail:rkarimi@lecom.edu as faculty members, to remember the things that facilitated our learning when we were students. One of the key factors that significantly contributed to the enhancement of my teaching skills was to approach teaching from the student s perspective as closely as possible, thus allowing me to effectively deliver class materials. The challenge was how to accomplish that. In order to come as close as possible to the students perspective, the teacher must once again think and see things as students do. When I was a student, I always learned more and enjoyed learning more when my teachers provided illustrations relevant to the class materials. I have found that same technique works well for my students today. Teaching biochemistry is considered a difficult task, especially when your students have different educational backgrounds. To illustrate my teaching methods I will use the topic of glycolysis, which I teach in a biochemistry course, as an example. OBJECTIVES Glycolysis is a broad topic within the section on carbohydrate metabolism on which students are usually given avastamountofmaterialtolearn.despitethatteaching glycolysis by itself requires a substantial amount of time and effort, if presented alone, it is a useless procedure for students to learn. A knowledge of other processes such as thermodynamics and enzymology is crucial to understanding glycolysis. Gluconeogenesis, citric acid cycle, and oxidative phosphorylation are other complex processes that, if not taught in conjunction with glycolysis, will leave the students with many questions later. Thermodynamics is a separate topic that requires at least an introductory level of understanding by students who study biochemistry. It is fairly common to teach glycolysis without giving any emphasis to thermodynamics. Indeed, many college professors simply deliver the 1

lecture on conceptual thermodynamics and hope that students will one day integrate all the terms and equations into an overall concept. This undesirably leads to students memorizing the material rather than learning it, resulting in a shallow understanding of this fundamental pathway in biochemistry. Many students are intimidated by the complexity of thermodynamics. This is usually not due to the instructor s teaching style, but to a lack of illustration and practical examples for thermodynamics. Although it may not be possible to provide illustrations for all of the terms and equations in thermodynamics, glycolysis can be used to illustrate this complext subject. Unlike thermodynamics, enzymology is often incorporated into biochemistry courses and as a result, is taught by biochemistry teachers at many pharmacy schools. This sequential procedure facilitates the teaching procedure for biochemistry teachers as they then know how much enzymology has been covered. When I turn the clock back to the time I was a student, I recall how much thermodynamics and enzymology helped me to understand glycolysis as an important concept in the carbohydrate metabolism rather than simply memorizing 10 complex steps in biochemistry. Therefore, it is critical to occasionally consider ourselves as students and see the world from their perspective. In doing so, we may realize the techniques that are important to effectively delivering class materials. 2 INSTRUCTIONAL DESIGN Glycolysis is one of the major pathways taught in biochemistry courses that is often linked to carbohydrate metabolism. The majority of the biochemistry textbooks present this topic after enzymology, while others cover both enzymology and thermodynamics (bioenergetics) before presenting glycolysis. 1 Glycolysis is a complex pathway consisting of 10 different steps. Each step requires a unique enzyme to carry out the reaction. The glycolytic pathway starts when one molecule of the 6-carbon glucose breaks down in 10 enzyme-catalyzed steps and ends when 2 molecules of a 3-carbon pyruvate are produced. Additional net products of glycolysis include 2 adenosine triphosphate (ATP) molecules and 2 reduced niotinamide adenine dinucleotide (NADH) molecules. Enzymology plays an important role in glycolysis because both enzyme kinetics and regulation are involved in this pathway. Energy expenses and releases regarding the different steps are also vital in understanding the glycolytic pathway. Lecture or lectures on enzymology prior to introducing glycolysis and carbohydrate metabolism are vital when introducing students to both enzyme kinetics and regulation. In the enzymology lecture(s) the fundamental concepts of enzyme kinetics, ie, enzyme-catalyzed reaction rates, and the factors influencing rates (such as temperature and concentration of substrate) should be taught. Another important area on which to focus is allosteric regulation of enzymes. The role of substrate concentration is of particular concern as it directly influences the rate of an enzyme-catalyzed reaction. In glycolysis there are 3 different irreversible enzymes, namely hexokinase, phosphofructokinase-1 (PFK-1), and pyruvate kinase, that regulate the influx of glucose into glycolysis. PFK- 1 plays a major role in the regulation of glycolysis. Using this part of glycolysis as an illustration, the role of the substrate concentration and the regulatory mode of the enzyme can be emphasized. Using a simple sigmoid curve, one can show that the catalytic rate of PFK-1 increases as the concentration of substrate, fructose 6-phosphate, increases. This is followed by a leveling off (plateau-like) of the curve which indicates that the enzyme is saturated with the substrate. The same enzyme can be used to illustrate the allosteric role of enzymes. Adenosine triphosphate (ATP) acts as an allosteric molecule to regulate the influx of glucose into glycolysis. ATP, at high concentration, binds to its allosteric site on PFK-1, distinct from the binding site of the substrate, to induce conformational change to PFK-1, thereby decreasing PFK-1 s affinity for its substrate. The entire process results in slowing the glycolytic pathway. 2 Another important approach to clarifying enzymology concepts is to discuss the role of 2 isozymes in carbohydrate metabolism, hexokinase and glucokinase (hexokinase IV). Although similar, the 2 enzymes act in different areas of the body; hexokinase in muscles and glucokinase in the liver. 3,4 The existence of these 2 isozymes indicates that the 2 different organs play different roles in carbohydrate metabolism. In other words, the liver maintains blood glucose levels and muscles, which lack this function, consume glucose for production of energy. A lack of enzyme kinetics and regulation leaves a gap in understanding the mechanisms for these 2 isozymes. Simply put, by having a high Michaelis constant (K m, 10mM), glucokinase plays a central role in the regulation of blood glucose levels. Consequently, the high K m of glucokinase promotes a persistent catalysis of glucose to glucose 6-phosphate until it reaches a saturated level. In addition, due to the proximity of K m to the concentration of substrate (ie, glucose in the blood, 4.5mM), glucokinase does not work at maximum velocity and thereby remains highly sensitive to small changes in the glucose concentration in the blood. This unique enzyme activity of glucokinase helps the liver respond and regulate blood glucose level, a unique and vital function of the liver. On the other hand, hexokinase, which functions

mainly in the skeletal muscles, is allosterically inhibited by its byproduct ie, glucose 6-phosphate. This property is unique for hexokinase, but not for glucokinase. The latter observation indicates that whenever the cellular level of glucose 6-phosphate increases (except in the liver), hexokinase is temporarily and reversibly inhibited. This allosteric regulation, as well as the allosteric regulation of PFK-1 by ATP, results in saving glucose and ATP, unless glycolysis is necessary. Another topic that is also crucial to understanding glycolysis is thermodynamics. It is through thermodynamics that the student learns about the direction of pathway, the interplay between the concentrations of substrate and product in each reaction, the rationale behind phosphorylation and dephosphorylation of substrates, and the overall standard free energy investment and payoff. In addition, it is thermodynamics that explains the direction and extent to which a chemical reaction proceeds, which in turn is explained by changes in 2 fundamental terms in thermodynamics, enthalpy and entropy. The basic concepts associated with 2 different but related quantities, ie, standard free energy change (DG9 o ) and actual free energy change (DG, often referred to as Gibbs free energy change) should be taught prior to glycolysis. Standard free energy change that is simply a constant and has an unchanged value for a given reaction describes how far and in what direction a given reaction, under standard conditions, should go to reach equilibrium. On the other hand, the actual free energy change, which is not a constant, but rather a variable, explains the spontaneity of a reaction. To further clarify this concept and the fact that DG and DG9 o are related to each other quantitatively, one can use the following equation, DG 5 DG9 o 1 RT In (product/reactant). In this equation, R and T refer to the gas constant and the absolute temperature, respectively. The DG explains how a nonspontaneous reaction (ie when the DG9 o has a positive value) can proceed spontaneously. This unique phenomenon has to do with the concentration of product and substrate in a given reaction. There are a few examples in glycolysis that can be used as illustrations to explain the role and the difference of these 2 quantities. For instance, the fourth step in glycolysis is thermodynamically unfavorable, ie, it requires a large positive DG9 o (23.8 kj/mol) to forward the catalysis of a 6-carbon molecule into two 3-carbon molecules. There is no available ATP or other energy source to explain how a nonspontaneous reaction, such as the fourth step in glycolysis, can proceed spontaneously. However, since these two 3-carbon molecules are immediately removed by the subsequent steps in glycolysis and providing a low ratio between the concentration of product and substrate, the DG ends up with a negative value that is characteristic of 3 a spontaneous reaction (see the above equation that illustrates how the logarithmic term becomes negative). Thermodynamics concepts identify and explain why the glycolytic pathway releases only a small amount (5%) of standard free energy of one glucose molecule. It emphasizes also the important role of the subsequent steps of glycolysis, ie, citric acid cycle and oxidative phosphorylation in releasing the remaining energy available (95%) from the same glucose molecule. To further illustrate the significant difference in the energy release, one has to follow the fate of the glycolytic end products: 2 pyruvate molecules, in the subsequent steps such as citric acid cycle and oxidative phosphorylation. Each of the 2 pyruvate molecules converts into acetyl-coa followed by oxidization in the citric acid cycle to produce electron carrier coenzyme NADH and reduced flavin adenine dinucleotide (FADH 2 ). These 2 coenzymes participate in the oxidative phosphorylation to release the remaining 95% energy that was originally stored in 1 glucose molecule. As indicated above, there is a connection between these 3 topics, ie, enzymology, thermodynamics, and glycolysis. Therefore, without enzymes (enzymology) or energy expenditure and release (thermodynamics), glycolysis could not occur; thus, without teaching these concepts, glycosis cannot be understood. At Lake Erie College of Osteopathic Medicine School of Pharmacy, biochemistry is taught in 2 subsequent courses, Biochemistry I and II. Each 3-credit hour course is taught on an accelerated level to our accelerated PharmD program (3-year program). The basic concepts of Gibbs free energy and standard-free energy, the laws of thermodynamics, and the function and structure of coenzymes, such as NADH and FADH, are taught prior to enzymology. In addition, the fundamental principles of enzyme kinetics are taught after thermodynamics. Since the 10 enzyme-catalyzed steps may overwhelm the students with structures and reactions, one can breakdown the entire glycolysis pathway into two 5-step pathways. The first pathway is an energy-investment pathway where the starting molecule is a 6-carbon molecule (glucose), which is thermodynamically favorable because of the ATP investment. The second pathway is an energypayoff pathway where the starting molecule is a 3-carbon molecule (glyceraldehyde 3-phosphate), which promotes formation of essential molecules such as ATP and NADH. Within each pathway the essential regulatory role of the irreversible reactions (2 in the first and 1 in the second pathway), including the role of PFK-1 as mentioned above, is emphasized. I have found glycolysis provides many illustrations and models for thermodynamics and enzymology. The discussion on glycolysis is extended to include the citric

acid cycle and oxidative phosphorylation. The latter 2 topics are the illustrative examples for glycolysis and the conclusion of the oxidative process of glucose molecules. DISCUSSION In many pharmaceutical science courses, students are intimidated by the structures and mechanisms of different molecules and pathways. My own experience indicates that no matter how attractive a subject is, explaining the rationale behind teaching the subject is essential. By presenting illustrations and explaining the reasons for learning a subject, the students become more motivated. On the other hand, no matter how much a student is motivated, the difficulty of the subject is always a barrier to learning the materials. Therefore, a crucial step in teaching a difficult concept is providing illustrations, either by giving examples or continuing into a subsequent subject for which illustrations and models can be easily found. Evidently, there is a positive relationship between learning and retention. Simply put, the more interesting the subject, the more students learn and the more likely they are to continue and graduate. 5 There is mutual interest between enzymology, thermodynamics, and glycolysis. While enzymology and thermodynamics serve as a background to glycolysis, glycolysis serves as an illustration of both enzymology and thermodynamics (see Figure 1). In these sequences and manner, not only are the students not confused or overwhelmed with the vast material on glycolysis, but they see connections and understand the importance of Figure 1. An interlocked-rings model between thermodynamics, enzymology, and glycolysis. This model shows that while thermodynamics and enzymology serve as background to glycolysis, glycolysis serves as an illustration of thermodynamics and enzymology. 4 learning glycolysis. It is really pointless to start glycolysis without going one step back and teaching enzymology and thermodynamics. In addition, you have to continue to teach the subsequent subjects, such as citric acid cycle and oxidative phosphorylation pathways, after glycolysis. The phrase cut to the chase will never work here. My own experience has shown that students who have a solid background in both thermodynamics and enzymology tend to retain the glycolysis information longer and apply it more effectively to other topics related to carbohydrate metabolism. These students will promote effective learning and have a positive approach toward pharmaceutical sciences that ultimately will assist them in their academic success. Every student s style of learning is unique; therefore, we as teachers should not limit our teaching to the learning style we favor. Instead, if a teaching technique is working well for another instructor, we should at least consider trying it in our own classroom. As a teacher one must always consider what is important to be taught and what are the necessary tools and techniques that make learning easier for the students. To cope with these tasks, one has to work as both teacher and student. No doubt that it is the teacher, as an immediate mentor, who decides what is important for the student s professional and academic growth. It is also the teacher who ultimately will use the tools and techniques to improve and facilitate the learning phase for students. However, at some point the teacher must put themselves in the students shoes and see things from a student s prospective. It is through this interpersonal exchange that a teacher can remain ahead of a student and realize how a student is thinking and how effectively the student is able to learn. If a teacher knows what the students need and how the students learn, he or she will be prepared, in advance, which results in a mutually enjoyable atmosphere for both the students and the teacher. In a student s mind, a difficult concept such as glycolysis could be a pure memorization concept that one only needs to remember during examinations. It is the teacher s responsibility to break down complex concepts into smaller, absorbable amounts of information. In doing this, the teacher should go back and introduce the basic concepts that play an important role in learning the complex concepts. As teachers, we should be focused on the quality of student learning rather than on the quantity of information presented. Biochemistry concepts, including glycolysis, are learned effectively if they are presented in a variety of contexts and illustrations. For students, it is also important to know why learning the complex concept is crucial for their knowledge. Often, a gap between students learning and the rationale behind learning result in students attrition.

Science courses, and biochemistry in particular, are everchanging topics. Consequently, we as teachers are responsible to extend our perception of course design, no matter how much the perception demands. SUMMARY Glycolysis, carbohydrate metabolism, thermodynamics, and enzymology are complex and complicated parts of biochemistry that require a substantial amount of effort and time to learn. Illustrations and practical examples in biochemistry are useful tools that facilitate student learning. While thermodynamics and enzymology are essential to assist student learning in glycolysis, glycolysis and carbohydrate metabolism provide illustrations of thermodynamics and enzymology. The novel interlocked rings model presented represents how different teaching tools can be employed in biochemistry to support students learning. ACKNOWLEDGEMENTS The author would like to thank Drs. Seher Khan and Fariba Safaiyan and Ms. Dru Howells who kindly reviewed the manuscript and provided comments and suggestions. REFERENCES 1. Nelson DL, Cox MM. Lehninger Principles of Biochemistry, 4th ed. New York, NY: W.H. Freeman and Company; 2005:481. 2. Schirmer T, Evans PR. Structural basis of the allosteric behaviour of phosphofructokinase. Nature. 1990;43:140-5. 3. Nelson DL, Cox MM. Lehninger Principles of Biochemistry, 4th ed. New York, NY: WH Freeman and Company; 2005:576-78. 4. Cornish-Bowden A, Cardenas ML. Hexokinase and glucokinase in liver metabolism. Trends Biochem Sci. 1991;16:281-2. 5. Vincent T. Promoting Student Retention: Lesson learned from the United States. Proceedings of the 11th Annual Conference of the European, Access Network, Prato, Italy. July 19, 2002. Available at: http://soeweb.syr.edu/faculty/vtinto/files/eanspeech.pdf. Accessed December 27, 2004. 5