electron transport chain

Examples of electron transport chain in the following topics:

• Electron Transport Chain

  • The electron transport chain uses the electrons from electron carriers to create a chemical gradient that can be used to power oxidative phosphorylation.
  • The electron transport chain is an aggregation of four of these complexes (labeled I through IV), together with associated mobile electron carriers.
  • Once it is reduced to QH2, ubiquinone delivers its electrons to the next complex in the electron transport chain.
  • This enzyme and FADH2 form a small complex that delivers electrons directly to the electron transport chain, bypassing the first complex.
  • The electron transport chain is a series of electron transporters embedded in the inner mitochondrial membrane that shuttles electrons from NADH and FADH2 to molecular oxygen.

• Electron Donors and Acceptors

  • Electrons can enter the electron transport chain at three levels: dehydrogenase, the quinone pool, or a mobile cytochromeelectron carrier.
  • Individual bacteria use multiple electron transport chains, often simultaneously.
  • A common feature of all electron transport chains is the presence of a proton pump to create a transmembrane proton gradient.
  • Since electron transport chains are redox processes, they can be described as the sum of two redox pairs.
  • The situation is often summarized by saying that electron transport chains in bacteria are branched, modular, and inducible.

• Chemiosmosis and Oxidative Phosphorylation

  • During chemiosmosis, electron carriers like NADH and FADH donate electrons to the electron transport chain.
  • At the end of the pathway, the electrons are used to reduce an oxygen molecule to oxygen ions.
  • The extra electrons on the oxygen attract hydrogen ions (protons) from the surrounding medium and water is formed.
  • In oxidative phosphorylation, the hydrogen ion gradient formed by the electron transport chain is used by ATP synthase to form ATP.
  • Describe how the energy obtained from the electron transport chain powers chemiosmosis and discuss the role of hydrogen ions in the synthesis of ATP

• ATP Yield

  • The process of glycolysis only produces two ATP, while all the rest are produced during the electron transport chain.
  • Clearly, the electron transport chain is vastly more efficient, but it can only be carried out in the presence of oxygen.
  • For example, the number of hydrogen ions the electron transport chain complexes can pump through the membrane varies between species.
  • NAD+ is used as the electron transporter in the liver, and FAD+ acts in the brain.
  • Glycolysis on the left portion of this illustration can be seen to yield 2 ATP molecules, while the Electron Transport Chain portion at the upper right will yield the remaining 30-32 ATP molecules under the presence of oxygen.

• Electron Donors and Acceptors in Anaerobic Respiration

  • In anaerobic respiration, a molecule other than oxygen is used as the terminal electron acceptor in the electron transport chain.
  • This method still incorporates the respiratory electron transport chain, but without using oxygen as the terminal electron acceptor .
  • Many different types of electron acceptors may be used for anaerobic respiration.
  • Acetogenesis is a type of microbial metabolism that uses hydrogen (H2) as an electron donor and carbon dioxide (CO2) as an electron acceptor to produce acetate, the same electron donors and acceptors used in methanogenesis.
  • Electron flow in these organisms is similar to those in electron transport, ending in oxygen or nitrate, except that in ferric iron-reducing organisms the final enzyme in this system is a ferric iron reductase.

• Control of Catabolic Pathways

  • Catabolic pathways are controlled by enzymes, proteins, electron carriers, and pumps that ensure that the remaining reactions can proceed.
  • Enzymes, proteins, electron carriers, and pumps that play roles in glycolysis, the citric acid cycle, and the electron transport chain tend to catalyze non-reversible reactions.
  • Specific enzymes of the electron transport chain are unaffected by feedback inhibition, but the rate of electron transport through the pathway is affected by the levels of ADP and ATP .
  • This change in the relative concentration of ADP to ATP triggers the cell to slow down the electron transport chain.
  • Levels of ADP and ATP affect the rate of electron transport through this type of chain transport.

• Processes of the Light-Dependent Reactions

  • Because this state of an electron is very unstable, the electron is transferred to another molecule creating a chain of redox reactions called an electron transport chain (ETC).
  • The electrons travel through the chloroplast electron transport chain to photosystem I (PSI), which reduces NADP+ to NADPH.
  • The electron transport chain moves protons across the thylakoid membrane into the lumen.
  • The light excites an electron from the chlorophyll a pair, which passes to the primary electron acceptor.
  • In (b) photosystem I, the electron comes from the chloroplast electron transport chain.

• Anoxygenic Photosynthetic Bacteria

  • The electron transport chain (ETC) of green sulfur bacteria uses the reaction centre bacteriochlorophyll pair, P840.
  • If the electron leaves the chain to reduce NAD+, P840 must be reduced for the ETC to function again.
  • The electron transport chain of purple non-sulfur bacteria begins when the reaction center bacteriochlorophyll pair, P870, becomes excited by the absorption of light.
  • Excited P870 will then donate an electron to Bacteriopheophytin, which then passes it on to a series of electron carriers down the electron chain.
  • The electron returns to P870 at the end of the chain so it can be used again once light excites the reaction-center.

• Routing

  • Routing is performed for many kinds of networks, including the telephone network (circuit switching), electronic data networks (such as the internet), and transportation networks.
  • Transport engineers use mathematical graph theory to analyze a transport network to determine the flow of vehicles (or people) through it.
  • A transport network may combine different modes of transport.
  • At the tactical level of supply chain activities, the transportation strategy of goods must be considered.
  • In order to reduce costs, companies often look for ways to streamline routes and supply chain activities.

• Special topic: supply chain management

  • Supply chain management is the business function that coordinates and manages all the activities of the supply chain, including suppliers of raw materials, components and services, transportation providers, internal departments, and information systems.
  • Exhibit 31 illustrates a supply chain for providing packaged milk to consumers.
  • In the manufacturing sector, supply chain management addresses the movement of goods through the supply chain from the supplier to the manufacturer, to wholesalers or warehouse distribution centers, to retailers and finally to the consumer.
  • For example, a retail store that sells electronic products may contract with an outside business to provide installation services to its customers.
  • The supply chain is not just a one way process that runs from raw materials to the end customer.