Everything about Metabolic Pathways totally explained
In
biochemistry, a
metabolic pathway is a series of
chemical reactions occurring within a
cell. In each pathway, a principal chemical is modified by
chemical reactions.
Enzymes
catalyze these reactions, and often require dietary minerals, vitamins and other
cofactors in order to function properly. Because of the many chemicals that may be involved, pathways can be quite elaborate. In addition, many pathways can exist within a cell. This collection of pathways is called the
metabolic network. Pathways are important to the maintenance of
homeostasis within an
organism.
Metabolism is a step by step modification of the initial molecule to shape it into another product. The result can be used in one of three ways.
- Stored by the cell.
- Be used immediately, as a metabolic product.
- Initiate another metabolic pathway, called a flux generating step.
A molecule called a
substrate enters a metabolic pathway depending on the needs of the cell and the availability of the substrate. An increase in concentration of
anabolical and
catabolical end products would slow the metabolic rate for that particular pathway.
Overview
Metabolic pathways are composed of a series of biochemical reactions that are connected by their intermediates: the reactants (or substrates) of one reaction are the products of the previous one, and so on. Metabolic pathways are usually considered in one direction (although all reactions are chemically reversible, conditions in the cell are such that it's thermodynamically more favorable for flux to be in one of the directions).
» *
Glycolysis was the first metabolic pathway discovered:
#As
glucose enters a cell it's immediately
phosphorylated by
ATP to
glucose 6-phosphate in the irreversible first step. This is to prevent the glucose leaving the cell.
» #In times of excess
lipid or
protein energy sources
glycolysis may run in reverse (
gluconeogenesis) in order to produce
glucose 6-phosphate for storage as
glycogen or
starch.
Metabolic pathways are often regulated by feedback inhibition, or by a cycle where one of the products in the cycle 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
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:
Glycolysis
Anaerobic respiration
Krebs cycle / Citric acid cycle
Oxidative phosphorylation
Other pathways occurring in (most or) all living organisms include:
Fatty acid oxidation (β-oxidation)
Gluconeogenesis
HMG-CoA reductase pathway (isoprene prenylation chains, see cholesterol)
Pentose phosphate pathway (hexose monophosphate shunt)
Porphyrin synthesis (or heme synthesis) pathway
Urea cycle
Creation of energetic compounds from non-living matter:
Photosynthesis (plants, algae, cyanobacteria)
Chemosynthesis (some bacteria)Further Information
Get more info on 'Metabolic Pathways'.
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