A biochemical pattern, the Krebs’s cycle (or T.C.A. cycle) : discovery, diffusion, teaching at university and at secondary school

Beatrice Desbeaux Salviat, 15 septembre 1997

This research aims at translating into pedagogical acts the questions concerning biochemical knowledge. An epistemological and historical reflection on contents of biochemistry shows how the objectives of this discipline differ from those of chemistry and those of biology, and exhibits the difficulties of an experimental approach of complex phenomena occurring in living things. The Tri Carboxylic Acid Cycle (TCA or citric acid cycle), essential in the study of metabolism, designates a biochemical process which can be represented by patterns ; it has been chosen as an object of a thorough study allowing many reflections and propositions for teaching at university and at secondary school. Taught traditionally in a dogmatic way, without any reference to the context of its elaboration, it is an emblematic example of biochemical knowledge ; epistemology and history of science are needed to teach it in a different way. Evidence that the building of this knowledge was not a linear process is given by historical research on the discoverer of the cycle, H.A. Krebs, and on the analyses of his publications from 1937 to 1981. The study of its diffusion into the community of scientists reveals that the cycle has been modified many times, with successive regressions and progressions caused by the available theories and techniques. The obtained data permit, at the university, to explore three new avenues : to make a thorough examination of the concept of scientific knowledge, of the concept of pattern, and then of reductionism. At secondary school, even if it was used for four years in the French curricula, the TCA cycle is definitely not a knowledge that the pupil must master. Questions from 17 years old pupils about living things arise when they proceed to an adaptation of Krebs’s experiments, using computer assisted techniques,  providing them with experimental referent.