Metabolic pathway

In metabolic network. Pathways are important to the maintenance of homeostasis within an organism.

Overview

Metabolic pathways often have these properties:

• They contain many steps, like a cascade. The first step is usually irreversible. The other steps need not be irreversible and in many cases, the pathway can go in opposite direction depending on the current need of the cell.

• Glycolysis features excellent examples of these features:

1. As ATP to glucose 6-phosphate in the irreversible first step. This is to prevent the glucose leaving the cell.
2. In times of excess starch.

• They are regulated, usually by 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. These occur within all living organisms in some forms:

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

Other pathways occurring in (most or) all living organisms include:

• Fatty acid oxidation (β-oxidation)
• Gluconeogenesis
• cholesterol)
• Pentose phosphate pathway (hexose monophosphate shunt)
• heme synthesis) pathway
• Urea cycle

Creation of energetic compounds from non-living matter:

• cyanobacteria)
• Chemosynthesis (some bacteria)

See also

• Metabolism
• Metabolic network
• Metabolic network modelling

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