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Educat ion to try to sort out the problems which are relevant to teaching of Biochemistry and life sciences in colleges and universities in Karnatak. (2) It was desired that all participants write a simple experimental manual for the benefit of college teachers. (3) It was suggested that universities should recognise and organise Workshops, Seminars or Short Courses in which faculty can explore education theory and practice and thus increase their confidence ability and effectiveness as educators.

References t Vella F (1991) Biochem Educ 19, 178

2Vella F (1992) Biochem Educ 20, 17

0307-4412(95)00070-4

An Easy Approach to the Calvin Cycle

GUSTAVO GONZALEZ

Secci6n Bioquimica, Instituto de Quimica Universidad CatOlica de Valparaiso Valparaiso, Chile

Introduction The conversion of CO2 into glucose in photosynthesising cells occurs in a metabolic pathway known as Calvin cycle. It may function in the absence of light and for this reason is often called the dark phase of photosynthesis.

The conversion is achieved by the linkage of CO2 to a pentose bisphosphate (ribulose 1,5-bisphosphate) giving rise to a transitory six-carbon intermediary which is broken into two 3-phosphoglycerate molecules that are phosphorylated with ATP and reduced with N A D P H to produce two glyceraldehyde 3-phosphate molecules. These two triose phosphates are then converted to glucose via fructose-bisphosphate and fructose-6-phosphate.

In the cell the objective of this process is to accomplish a net synthesis of one glucose from six CO2 with no net consumption of the six ribulose-bisphosphate involved in the CO2 fixation. Therefore a regeneration or recovery pathway of these ribulose molecules must be operating.

The recovery pathway involves the participation of several triose-phosphates in different reactions, configur- ing a scheme that at first glance gives the impression of great complexity. Many Biochemistry textbooks present Calvin cycle as a tangled set of reactions that gives to the student the feeling of something complex - - but few students make the effort to try to understand the process.

New approach I present here a different approach to the Calvin cycle that may promote a more facile access to its study by showing the simplicity of its organization. The cycle is considered in two parts: (1) CO2 fixation and synthesis of triose- phosphates and a hexose, and (2) ribulose-bisphosphate regeneration.

BIOCHEMICAL EDUCATION 23(3) 1995

(1) COe fixation and synthesis of triose-phosphate and a hexose

RuBP + COz ~ 2 P G A 2 ATP, 2 NADPH

2 G3P 2 ADP, 2NADP

---> G3P + D H A P ---> FBP ---> F6P Pi (1)

This set of reactions produces F6P (which may be converted into glucose) from one RuBP and one CO2. Since the objective of the process is the net synthesis of one F6P from six CO2, the analysis starts multiplying by six:

6 RuBP + 6 C O 2 ~ 12 P G A ~ 12 G3P --~ 6 G3P + 6 D H A P --* 6 FBP --~ 6 F6P (2)

But since the synthesis of one F6P is sufficient for the formation of only one hexose from six CO2, reaction set 2 may end as:

12 G3P ---> 10 G3P + (G3P + D H A P ---> FBP ---> F6P) (3)

This equation gives an account of the synthesis of one hexose from six CO2 but also allows the diversion of the remaining ten triose-phosphates (10 x 3C = 30C) to regenerate the six RuBP (6 x 5C = 30C) originally used to fix six CO2. The next stage consists then in the following overall reaction:

10 G3P ~ 6 RuBP (4)

(2) Ribulose-bisphosphate regeneration For this stage in the cycle it is necessary to look on the ten triose phosphates (10 G3P) available in eqn 4 in the form (6 G3P + 4 D H A P ) because triose phosphate isomerase can transform G3P into DHAP. The following reactions sequence now shows the formation of RuBP from triose phosphate:

aldolase phosphatase G3P + D H A P > FBP ~ F6P + Pi

transketolase F6P + G3P ~ E4P + X5P

aldolase E4P + D H A P ~ SHBP

phosphatase SHBP + H 2 0 > SHP + P~

transketolase SHP + G3P > R5B + X 5 P

isomerase R5P > Ru5P

epimerase 2 X5P ~ 2 Ru5P

kinase 3 Ru5P + 3 ATP ~ 3 RuBP + 3 A D P

3 ATP 3ADP Sum: 3 G3P + 2 D H A P ~. ~" 3 RuBP

This overall reaction accounts for the participation of half of the available triose phosphates: therefore the other half can yield the final product of six ribulose bisphosphates which were originally employed in the fixation of 6 CO2 (eqn 2). The overall reaction for .the complete regener- ation will therefore be:

6 ATP 6 ~DP 6 G 3 P + 4 D H A P ~ - 6 R u B P (5)

Conclusion Calvin cycle can be viewed then as the combination of two sets of reactions. The first is the formation of fructose phosphate (combination of reaction sets 2 and 3) and the second is the regeneration of ribulose bisphosphate (reaction set 5). The result is the synthesis of fructose phosphate from six CO2.

12 ATP + 12 N A P H + 6 RuBP + 6 CO2 --~ 6 G3P + 4 D H A P + F6P + 12 ADP

+ 13 Pi + 12 NADP + (2) and (3)

6 A T P + 6 G 3 P + 4 D H A P - - * 6 R u B P + 6 A D P + 4 P i (5)

Sum: 18 ATP + 12 N A D P H + 6 C O 2 ---) F6P + 18 AD P + 17 Pi + 12 N A D P +

Figure 1 gives an overview of the Calvin cycle.

11~ NAI=~P Py~12 G 3 P ~ ' ~ I ~ 1 2 ADP

12PGA ~ZNADP* 10G3P IZ Pi

6RuBP

G3P 2G3P -~* DI.~'A~-~ F a P p-~ F 6 P

2G3P ÷ 2DHAP

\ 2FBP

6ATP/ADP 6Ru5P

P ,%%

4X5P ~ 263P 2DHAP 2E4P + 2X5P

k~ 2XSP + 2 R S P / 2SHBP / ~ ~ - ' " E - - 2 S H P z~'-~p~ ~

Figure 1 The Calvin Cycle. Abbreviations: DHAP: Di- hydroxyacetone phosphate, E4P: Erythrose 4-phosphate, F6P: Fructose 6-phosphate, FBP: Fructose 1,6-bisphos- phate~ G3P: Glyceraldehyde 3-phosphate, PGA: 3-phos- phoglycerate (glycerate 3-phosphate), R5B: Ribose 5- phosphate, Ru5P: Ribulose 5-phosphate, RuBP: Ribulose 1,5-bisphosphate, SHP: Sedoheptulose 7-phosphate, SHBP: Sedoheptulose 1, 7-bisphosphate, X5P: Xylulose 5- phosphate

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0307-4412(95)00022-4

Drama: A Novel Evaluation Tool

ENEIDA DE PAULA, CAETANO DA COSTA DENISE VAZ DE MACEDO

Departamento de Bioquimica, Instituto de Biologia Universidade Estadual de Campinas CP 6109, CEP 13083-970, Campinas, SP Brasil

and

Introduction In traditional biochemistry courses there is an agreement between teacher and student concerning the learning process: the goal is achieved when the students memorize certain pathways, names and chemical structures. This need for memorization can make basic biochemistry classes boring, difficult and even "useless" in the eyes of the students. Curiously and paradoxically, the beautiful logic of life, whose main characteristic is simplicity, becomes an impossible puzzle. In careers such as Physical Education, Nursing, etc, with only a recent scientific tradition, it is even more difficult for teachers to hold the students' attention. In particular, when considering a Biochemistry course for Physical Education students using the tra- ditional approach, we may often feel that students are failing to appreciate the relationship between biochem- istry and exercise (unbelievable though this may be), making teaching difficult and unrewarding. Because of this, teachers dislike giving classes to Physical Education students.

The challenge of using new teaching and learning tools increases with the new generation: the new students are different from those of a few years ago. They are more 'visual' and ' touch-oriented' , and less and less prepared for lectures or classes with poor audio-visual resources. These students require more and more motivation, including the use of practical classes closely related to the lectures so that the matter as a whole can be visualised.

There is a worldwide tendency towards the populariz- ation of sport. Sports are related to a better life quality and most university students practice some kind of sport and are concerned about fitness and good nutrition. This is particularly true and relevant of course, for under- graduate students of Physical Education, since their field of work includes training (when they are athletes), coaching (other athletes) and teaching new coaches. This is a good reason for making great efforts to ensure that Basic Biochemistry, mainly the metabolic aspects, is one of the most interesting and fascinating courses from the point of view of these students, and it is important that they are able to fully understand all the topics. If they understand this background, it is clear that this knowledge makes them better prepared as compared to other professionals trained according to the 'memorization school'.

BIOCHEMICAL EDUCATION 23(3) 1995