The thematic unit consists of the study of energy transformations in living organisms or bioenergetics, dedicated to issues such as the application of thermodynamic laws to biological processes, respiration, or the light phase of photosynthesis. The first topic is an introduction to define the basic concepts in the study of cellular energy transformations. Then the central metabolic pathways shared by most living organisms are studied. Topics routes will be studied within global patterns of metabolism and highlights the objectives and general aspects, before proceeding to the detailed analysis of the reactions. In this analysis, we studied the chemical processing taking place and its energy aspects. Importantly, the interconnection of the various routes and their coordinated regulation are also discussed. Metabolism begins with the study of (1) carbohydrates: glycolysis-gluconeogenesis, acetyl-CoA and the citric acid cycle, and the route of the pentose phosphate. After anatomy of the mitochondria, the mitochondrial transport systems, and the respiratory chain of the inner mitochondrial membrane are studied, continuing with the description of ATP production by means of oxidative reactions. Different ATP synthases, enzymes responsible for the synthesis of ATP, are studied, as well as the different relative orientations of these enzymes in different systems and the reaction mechanism. The unit then examines the electron transport chain of the thylakoid membrane in the chloroplast photosynthetic organisms, the photosynthetic assimilation of CO2 and glycogen metabolism. Next, the (2) metabolism of simple lipids (fatty acids) and more complex lipids (triacylglycerols, phosphoglycerides and sphingolipids) are addressed. Cholesterol precursor and functions are also discussed in the biosynthesis of steroid hormones and bile salts. It continues with the (3) metabolism of nitrogen compounds and oxidative degradation of the amino acids, which is divided into two parts: the destination of the nitrogen and the carbon skeletons. The nitrogen cycle in the biosphere and biological fixation of atmospheric nitrogen by nitrogenase is also presented, as well as the (4) metabolism of purine and pyrimidine nucleotides that all living organisms are able to synthesize. Finally an integrated vision of intermediary metabolism and its control is sought.