In biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell. Biochemistry is the study of the chemical processes in living Organisms It deals with the Structure and function of cellular components such as Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called In each pathway, a principal chemical is modified by chemical reactions. A chemical reaction is a process that always results in the interconversion of Chemical substances The substance or substances initially involved in a chemical reaction are called Enzymes catalyze these reactions, and often require dietary minerals, vitamins and other cofactors in order to function properly. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst A cofactor is a non-protein Chemical compound that is bound (either tightly or loosely to an Enzyme and is required for Catalysis. 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. A metabolic network is the complete set of metabolic and physical processes that determine the physiological and biochemical properties of a cell Pathways are important to the maintenance of homeostasis within an organism. Homeostasis (from Greek: ὅμος hómos, "equal" and ιστημι istēmi, "to stand" lit

Metabolism is a step by step modification of the initial molecule to shape it into another product. Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. 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. Anabolism is the set of Metabolic pathways that construct molecules from smaller units For the related metabolic process see Anabolism. Catabolism is the set of Metabolic pathways which break down molecules into

Contents 1 Overview 2 Major metabolic pathways 2.1 Cellular respiration 3 See also 4 External links

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 is thermodynamically more favorable for flux to be in one of the directions).

• Glycolysis was the first metabolic pathway discovered:

1. As glucose enters a cell it is immediately phosphorylated by ATP to glucose 6-phosphate in the irreversible first step. See also Gluconeogenesis, which carries out a process wherein glucose is synthesized rather than catabolized Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. Phosphorylation is the addition of a Phosphate (PO4 group to a Protein molecule or a small molecule Adenosine-5'-triphosphate ( ATP) is a multifunctional Nucleotide that is most important as a " molecular currency" of intracellular Energy Glucose 6-phosphate (also known as Robison ester) is Glucose sugar Phosphorylated on carbon 6 This is to prevent the glucose leaving the cell.
2. 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. Lipids are broadly defined as any fat- Soluble ( lipophilic) naturally-occurring Molecule, such as fats oils waxes cholesterol sterols fat-soluble Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl See also Gluconeogenesis, which carries out a process wherein glucose is synthesized rather than catabolized Gluconeogenesis (abreviated GNG) is a Metabolic pathway that results in the generation of Glucose from non- Carbohydrate carbon substrates such Glucose 6-phosphate (also known as Robison ester) is Glucose sugar Phosphorylated on carbon 6 Glycogen is a Polysaccharide of Glucose (Glc which functions as the secondary short term energy storage in Animal cells Starch, CAS # 9005-25-8 Chemical formula (C6H10O5n is a Polysaccharide

• 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). Control theory is an interdisciplinary branch of Engineering and Mathematics, that deals with the behavior of Dynamical systems The desired output Enzyme inhibitors are Molecules that bind to Enzymes and decrease their activity. The citric acid cycle, also known as the tricarboxylic acid cycle ( TCA cycle) or the Krebs cycle, (or rarely the Szent-Györgyi–Krebs cycle
• Anabolic and catabolic pathways in eukaryotes are separated by either compartmentation or by the use of different enzymes and cofactors. Anabolism is the set of Metabolic pathways that construct molecules from smaller units For the related metabolic process see Anabolism. Catabolism is the set of Metabolic pathways which break down molecules into Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex In Cell biology, an organelle (pronunciation /ɔː(rgəˡnɛl/ is a specialized subunit within a cell that has a specific function and is usually separately enclosed

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. Cellular respiration is the set of the metabolic reactions and processes that take place in Organisms cells to convert biochemical energy from A nutrient is food or chemicals that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment Adenosine-5'-triphosphate ( ATP) is a multifunctional Nucleotide that is most important as a " molecular currency" of intracellular Energy These occur within all living organisms in some forms:

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

See also

• Metabolism
• Metabolic network
• Metabolic network modelling

External links

• BioCyc: Metabolic network models for hundreds of organisms
• KEGG: Kyoto Encyclopedia of Genes and Genomes
• MetaCyc: A database of nonredundant, experimentally elucidated metabolic pathways (900+ pathways from more than 800 different organisms).
• Metabolism, Cellular Respiration and Photosynthesis - The Virtual Library of Biochemistry and Cell Biology
• PathCase Pathways Database System
• Interactive Flow Chart of the Major Metabolic Pathways
• A novel visualization for a Metabolic Pathway
• DAVID: Visualize genes on pathway maps
• Wikipathways: pathways for the people

See also Gluconeogenesis, which carries out a process wherein glucose is synthesized rather than catabolized See also Fermentation (biochemistry Anaerobic respiration (anaerobiosis refers to the Oxidation of molecules in the absence of Oxygen to produce The citric acid cycle, also known as the tricarboxylic acid cycle ( TCA cycle) or the Krebs cycle, (or rarely the Szent-Györgyi–Krebs cycle The citric acid cycle, also known as the tricarboxylic acid cycle ( TCA cycle) or the Krebs cycle, (or rarely the Szent-Györgyi–Krebs cycle Oxidative phosphorylation is a Metabolic pathway that uses energy released by the oxidation of Nutrients to produce Adenosine triphosphate (ATP Fatty acids are an important source of Energy for many organisms Gluconeogenesis (abreviated GNG) is a Metabolic pathway that results in the generation of Glucose from non- Carbohydrate carbon substrates such The mevalonate pathway or HMG-CoA reductase pathway or mevalonate-dependent (MAD route, is an important cellular Metabolic pathway present Isoprene is a common synonym for the chemical compound 2-methylbuta-13-diene Cholesterol is a Lipid found in the Cell membranes and transported in the Blood plasma of all Animals It is an essential component of mammalian The pentose phosphate pathway (also called Phosphogluconate Pathway or HexoseMonophosphate Shunt shunt is a process that serves to generate NADPH and the synthesis of pentose A porphyrin is a heterocyclic Macrocycle derived from four Pyrroline subunits interconnected via their α carbon atoms via Methine bridges (=CH- A heme ( American English) or haem ( British English) is a Prosthetic group that consists of an Iron atom contained in the center of The urea cycle (also known as the ornithine cycle) is a cycle of biochemical reactions occurring in many animals that produces Urea ( N[[hydrogen Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. Cyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of Bacteria that obtain their energy Chemosynthesis is the biological conversion of one or more carbon molecules (usually Carbon dioxide or Methane) and nutrients into organic matter using the Oxidation Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. A metabolic network is the complete set of metabolic and physical processes that determine the physiological and biochemical properties of a cell Metabolic network reconstruction and simulation allows for an in depth insight into comprehending the molecular mechanisms of a particular organism especially correlating the Genome

© 2009 citizendia.org; parts available under the terms of GNU Free Documentation License, from http://en.wikipedia.org
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic