Metabolic pathway

In biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell, catalyzed by enzymes, to achieve in either the formation of a metabolic product to be used or stored by the cell, or the initiation of another metabolic pathway (then called a flux generating step). Many of these pathways are elaborate, and involve a step by step modification of the initial substance to shape it into the product with the exact chemical structure desired.

Overview

Most metabolic pathways have these common properties:

• They are irreversible, usually because the first step is a committed step, such breakdown for the release of energy, that only runs in one direction.
• The pathways are regulated, usually by feedback inhibition, or may be a cycle where the end product starts the reaction again, such as the Krebs Cycle (see below).
• Anabolic and catabolic pathways in eukaryotes are separated by either compartmentation or by the use of different enzymes and cofactors.

Major metabolic pathways

Cellular respiration

Main article: Cellular respiration

Several distinct but linked metabolic pathways are used by cells to transfer the energy released by breakdown of fuel molecules to ATP:

1. Glycolysis
2. Anaerobic respiration
3. Krebs cycle / Citric acid cycle
4. Oxidative phosphorylation

Other pathways

• Fatty acid oxidation (β-oxidation)
• Gluconeogenesis
• HMG-CoA reductase pathway (cholesterol, isoprene prenylation chains)
• Pentose phosphate pathway (hexose monophosphate shunt)
• Porphyrin synthesis (or heme synthesis) pathway
• Urea cycle

See also

• catabolism

External links

• Open Directory Project: Metabolic Pathways
• Metabolism, Cellular Respiration and Photosynthesis - The Virtual Library of Biochemistry and Cell Biology
• KEGG: Kyoto Encyclopedia of Genes and Genomes