Share on Facebook Share on Twitter Email
Answers.com

Metabolic pathway

 
Biology Q&A: What is a metabolic pathway?

A metabolic pathway is a series of interconnected reactions that share common mechanisms. Each reaction is dependent on a specific precursor: a chemical, an enzyme, or the transfer of energy. One of the first studies of metabolic pathways was carried out in 1909 by the British physician Archibald Garrod (1857-1936). His study suggested a link between the inability to make a particular enzyme and inherited disease. The disease was alkaptonuria, a condition in which urine darkens upon exposure to air, due to the presence of the chemical alkapton. Garrod's discovery was one of the first incidents of a physical manifestation being tied to a specific metabolic disorder.

Previous question: What are nucleic acids?
Next question: How do cells store energy?


Search unanswered questions...
Enter a question here...
Search: All sources Community Q&A Reference topics
Wikipedia: Metabolic pathway
Top

In biochemistry, metabolic pathways are 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:

  • To be stored by the cell
  • To be used immediately, as a metabolic product
  • To 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 anabolic and catabolic end-products would slow the metabolic rate for that particular pathway.

Contents

Overview

Each metabolic pathway is 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. This is to prevent the glucose from 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.

Major metabolic pathways

 v  d  e 
Gtk-dialog-info.svg All pathway labels on this image are links, simply click to access the article.
A high resolution labeled version of this image is available here. Metabolism 790px.png


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. Krebs cycle / Citric acid cycle
  4. Oxidative phosphorylation

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

Creation of energetic compounds from non-living matter:

See also

External links



 
 

 

Copyrights:

Biology Q&A. The Handy Biology Answer Book. 2004 ©Visible Ink Press. All rights reserved.  Read more
Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Metabolic pathway" Read more