Preferred Label : Electron Transport Pathway;
NCIt related terms : Electron Transport Reaction in Mitochondria;
Alternative definition : BIOCARTA: The body gets energy through the oxidation of food such as glucose and fatty
acids. The chemical energy contained in these foods is extracted and converted until
it reaches a common form, the high-energy phosphate bonds of ATP. The hydrolysis of
ATP is highly favorable and is coupled to a variety of energetically unfavorable processes
to drive them forward. Most of the energy of glucose or fatty acids is extracted through
oxidation to produce the reduced high-energy electron carriers NADH and FADH2. From
there, the energy is transferred next to the electron transport system associated
with the mitochondrial inner membrane. This chain includes a series of protein complexes
and non-membrane cofactors that transfer the electrons from NADH and FADH2 in a series
of redox reactions from carrier to carrier. Oxygen is the final electron acceptor
at the end of the chain, resulting in the production of water. The oxygen we breathe,
and which is transported by hemoglobin in the blood to all of the tissues, serves
this purpose and allows electron transport to occur. As the electrons pass through
the chain, they transfer their energy to the complexes, which use the energy to pump
protons out of the mitochondrial matrix, creating a proton gradient across the inner
mitochondrial membrane. The chemical energy that started with glucose, and was transferred
to NADH and FADH2, is then converted to the energy of a concentration gradient. The
inner mitochondrial membrane is impermeable to protons on its own, so the energy of
the proton gradient is stable, waiting to be recaptured. The energy is recaptured
by ATP synthase in the inner mitochondrial membrane. This enzyme allows protons to
flow back down their concentration gradient across the membrane, and in the process
uses the energy of the gradient to drive ATP synthesis. The movement of the electrons
through electron transport, the proton gradient and ATP synthesis are all coupled
processes that require each other to occur. The cell does not store energy as ATP,
but only has enough ATP on hand for its immediate energy needs. If electron transport
ceases or is inhibited, then ATP synthesis also rapidly halts. This regulation ensures
that ATP production closely matches the needs of the cell. Glycolysis and the Krebs
cycle are also closely linked to the energy needs of the cell. The abundance of ATP,
NADH and pathway intermediates regulates key steps in these pathways so that they
are activated when energy is required to feed the electron transport system and they
are inhibited when not needed to save metabolic energy. If oxygen is absent, electron
transport and the Krebs cycle rapidly halt, leaving glycolysis and fermentation as
the main means of energy production. During aerobic exercise, the rapid consumption
of ATP leads to use of the proton gradient to make more ATP, increased electron transport
to regenerate the proton gradient, increased oxygen consumption, and increased activity
of the Krebs cycle and glycolysis to supply high energy electrons to drive electron
transport. Uncoupling agents allow protons to flow across the mitochondrial membrane
without producing ATP. The chemical compound dinitrophenol (DNP), for example, can
transport protons across the inner mitochondrial membrane without ATP synthase. In
the presence of dinitrophenol, energy is consumed to pump protons out of mitochondria,
but this energy is not recaptured in chemical form in ATP. Instead, this energy is
released as heat. Dinitrophenol was once used as diet remedy to lose weight without
exercise or diet, but this compound is a metabolic poison and resulted in deaths in
when purposefully given to humans. Proteins also can act as uncoupling agents in the
mitochondria. A mitochondrial uncoupling protein is found in brown adipose tissue.
An increase in the activity of uncoupling proteins increases heat production by allowing
protons to flow down their gradient without making ATP and may serve as ...;
NCIt note : The BIOCARTA Definition (ALT_DEFINITION) for this pathway concept was provided by
BioCarta. This property was not created by, nor is it maintained by the NCI Thesaurus
staff. Additionally, BioCarta is no longer updating its pathway data; thus, the BIOCARTA
Definition might be outdated or inaccurate. Please see the Terms and Conditions for
Use at http://www.biocarta.com/.;
Biocarta ID : h_etcPathway;
Origin ID : C39074;
UMLS CUI : C1516799;
Semantic type(s)
- has_gene_product_element
- pathway_has_gene_element
