Metabolic biochemistry is a century old field of science where organic chemists studied the reactions of carbon compounds in living cells, mainly using extracts from animal tissues (liver, skeletal muscle, brain) and plants (photosynthesis). The central pathway that links energy needs with biosynthetic pathways, the Krebs Cycle or Citric Acid Cycle, has been described in 1937. All biochemistry textbooks, therefore, contain basic information about the cellular metabolisms of a variety of organisms that can be considered factual. An introductory course like this one is designed to give an overview of these basic elements of intracellular conversions of chemical structures and energy storage. The great variety of textbooks is a living prove to the advanced state of biochemistry. Nevertheless, many details are still under active exploration in laboratories around the world. A plethora of unique chemical pathways in microorganisms, and cell type specific metabolic needs in animals and plants promise many future discoveries. The recent advances in genome sequencing and the concomitant establishment of databases of DNA and amino acid sequences (see NCBI; National Center for Biotechnology Information), protein structures (see PDB; Protein Data Base; Research Collaboratory for Structural Bioinformatics), and higher databases like metabolic pathway maps (see KEGG, EcoCyc, and other (metabolic pathway) databases), provide a gold mine for today's biochemical research. Biochemistry and molecular biology are transforming themselves into Proteomics and Genomics (see ExPasy; WWW server from the  Swiss Institute of Bioinformatics). Knowing the nucleotide sequence of a gene is a major step forward, but the work does and cannot stop there. Metabolism is the coordinated activity of thousands of enzymes that catalyze a similar number of substrates in cyclical and linear stepwise fashion. These pathways are the way of a cell to extract energy from and chemically modify molecular structures for biosynthetic purposes.