Electron Transport Chains
An electron transport chain, or ETC,
Step 1: Electrons enter the ETC from an electron donor, such as NADH or FADH2, which
Step 2: After the first red/ox reaction, the initial electron donor will become oxidized and the electron acceptor will become reduced. The difference in red/
Step 4: After usually multiple red/ox transfers,
Note: NADH AND FADH2 ARE NOT THE ONLY ELECTRON DONORS
Electrons entering the ETC do not have to come from NADH or FADH2. Many other compounds can serve as electron donors; the only requirements are (1) that there is an enzyme that can oxidize the electron donor and then reduce another compound, and (2) that the ∆E0' is positive (e.g., ΔG<0). Even a small amount of free energy transfers can add up. For example, there are bacteria that use H2 as an electron donor. This is not too difficult to believe because the half reaction 2H+ + 2
What are the complexes of the ETC?
ETCs comprise a series (at least one) of membrane-associated red/ox proteins or (some are integral) protein complexes (complex =
How do ETC complexes transfer electrons?
As previously mentioned,
This use of prosthetic groups by members of ETC is true for
The electron and proton carriers
- Flavoproteins (Fp), these proteins contain an organic prosthetic group called a flavin, which is the actual moiety that undergoes the oxidation/reduction reaction. FADH2 is an example of
- Quinones are a family of lipids, which means they are soluble within the membrane.
- We also note that
we consider NADH and NADPH electron (2e-) and proton (2 H+) carriers.
- Cytochromes are proteins that contain a heme prosthetic group. The heme can carry a single electron.
- Iron-Sulfur proteins contain a nonheme iron-sulfur cluster that can carry an electron. We often abbreviate the prosthetic group as Fe-
Aerobic versus anaerobic respiration
We humans use oxygen as the terminal electron acceptor for the ETCs in our cells. This is also the case for many of the organisms we intentionally and frequently interact with (e.g. our classmates, pets, food animals, etc). We breathe in oxygen; Our cells take it up and transport it into the mitochondria, where it becomes the final acceptor of electrons from our electron transport chains. We call the process where oxygen
While we may use oxygen as the terminal electron acceptor for our respiratory chains, this is not the only mode of respiration on the planet. The more general processes of respiration evolved when oxygen was not a major component of the atmosphere. As a result, many organisms can use a variety of compounds, including nitrate (NO3-), nitrite (NO2-), even iron (Fe3+) as terminal electron acceptors. When oxygen is NOT the terminal electron acceptor, we refer the process to as anaerobic respiration. Therefore, respiration or oxidative phosphorylation does not require oxygen at all; It requires a compound with a high enough reduction potential to act as a terminal electron acceptor, accepting electrons from one complex within the ETC.
The ability of some organisms to vary their terminal electron acceptor provides metabolic flexibility and can ensure better survival if any given terminal acceptor is in limited supply. Think about this: in the absence of oxygen, we die; but other organisms can use a different terminal electron acceptor when conditions change to survive.
Possible NB Discussion Point
Nature has figured out how to use different molecules as terminal electron acceptors of ETCs. Yet humans
A generic example: A simple, two-complex ETC
The figure below depicts a generic electron transport
Figure 1. Generic 2 complex electron transport chain. In the figure, DH is the electron donor (donor reduced), and D is the donor oxidized.
Detailed look at aerobic respiration
The eukaryotic mitochondria have evolved a very efficient ETC. There are four complexes composed of proteins, labeled I
Figure 2. 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.
To start, NADH delivers two electrons to the first protein complex. This complex, labeled I in Figure 2, includes flavin mononucleotide (FMN) and iron-sulfur (Fe-S)-containing proteins. FMN, which is derived from vitamin B2, also called riboflavin, is one of several prosthetic groups or cofactors in the electron transport chain. Prosthetic groups are organic or inorganic, nonpeptide molecules bound to a protein that facilitate its function; prosthetic groups include coenzymes, which are the prosthetic groups of enzymes. We also call the enzyme in Complex I NADH dehydrogenase. This protein complex contains 45 individual polypeptide chains. Complex I can pump four hydrogen ions across the membrane from the matrix into the intermembrane space helping to generate and maintain a hydrogen ion gradient between the two compartments separated by the inner mitochondrial membrane.
Q and Complex II
Complex II directly receives FADH2, which does not pass through Complex I. The compound connecting the first and second complexes to the third is ubiquinone (Q). The Q molecule is lipid soluble and freely moves through the hydrophobic core of the membrane. Once reduced, (QH2), ubiquinone delivers its electrons to the next complex in the electron transport chain. Q receives the electrons derived from NADH from Complex I and the electrons derived from FADH2 from Complex II, succinate dehydrogenase. Since these electrons bypass and thus do not energize the proton pump in the first complex, fewer ATP molecules
The third complex is composed of cytochrome b, another Fe-S protein, Rieske center (2Fe-2S center), and cytochrome c proteins; we also call this complex cytochrome oxidoreductase. Cytochrome proteins have a prosthetic group of heme. The heme molecule is like the heme in hemoglobin, but it carries electrons, not oxygen. As a result, the iron ion at its core is reduced and oxidized as it passes the electrons, fluctuating between different oxidation states: Fe2+ (reduced) and Fe3+ (oxidized). The heme molecules in the cytochromes have slightly different characteristics because of the effects of the different proteins binding them, giving slightly different characteristics to each complex. Complex III pumps protons through the membrane and passes its electrons to cytochrome c for transport to the fourth complex of proteins and enzymes (cytochrome c is the acceptor of electrons from Q; however, whereas Q carries pairs of electrons, cytochrome c can accept only one at a time).
If the membrane were open to diffusion by protons, the ions would
Possible NB Discussion Point
Cyanide inhibits cytochrome c oxidase, a component of the electron transport chain. If cyanide poisoning occurs, would you expect the pH of the
In healthy cells,
Figure 4. In oxidative phosphorylation,
The electron transport chain or ETC is tightly coupled to the process of oxidative phosphorylation via the atp synthase system for the production of useful energy for metabolism in the form of ATP. These coupled processes are present in all mitochondria, which are present in all plant and animal life above the level of microbes. Even in the microbes, there are ETCs embedded in the cell membranes, even though they don't possess mitochondria.
A normal animal cell will have on the order of a thousand mitochondria, and each mitochondrion has on the order of a thousand ETCs, so a cell has something on the order of a million of these coupled energy tools! (Ahern)
Electron transport chain
Electron Transport Chain Definition
The electron transport chain is a cluster of proteins that transfer electrons through a membrane to create a gradient of protons that creates ATP (adenosine triphosphate) or energy that is needed in metabolic processes for cellular function.
electron transport chain (respiratory chain)
Usually, mitochondrial electron transport.
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The Electron Transport Chain
1) The electron transport chain is used to generate ATP (energy) in most organisms- both prokarytoic and eukaryotic.
2) NADH and FADH2 generated from glycolysis, pyruvate oxidation and the citric acid cycle are used to pump protons across a phospholipid bi-layer membrane .
and Energy Production Explained
A Guide to Different Types of Pathogens .
/ oxidative phosphorylation:
What = using hydrogen to produce ATP (see chemiosmotic theory).
Where = inner mitochondrial membrane.
In this stage all of the NADH and FADH that has been produced in the previous stages is converted into ATP. This takes place in the cristae of the mitochondria. The NADH and FADH electrons move.
In a cell membrane, electron carriers and enzymes positioned in an organized array that enhance oxidation-reduction reactions such systems function in the release of energy that is used in ATP formation and other reactions.
Many cyanobacteria are able to reduce nitrogen and carbon dioxide under aerobic conditions, a fact that may be responsible for their evolutionary and ecological success. The water-oxidizing photosynthesis is accomplished by coupling the activity of photosystem (PS) II and I (Z-scheme).
: a series of four large, multi-protein complexes embedded in the inner mitochondrial membrane that accepts electrons from donor compounds and harvests energy from a series of chemical reactions to generate a hydrogen ion gradient across the membrane .
A process that uses electron transport to power the transport of protons (H+), leading to the production of ATP. It is an important part of cellular respiration (following the Krebs cycle) and photosynthesis.
ETC &rarr inner membrane/cristae of mitochondria .
. Electrons from the oxidative reactions in the earlier stages of cell respiration pass along the chain.
A sequence of electron-carrier molecules (membrane proteins) that shuttle electrons during the redox reactions that release energy used to make ATP.
a system carrier molecules which transfer electrons from one to the other, releasing energy for the production of ATP
Electrophoresis a method used to separate a mixture of charged molecules
Element any substance that cannot be broken down further by chemical means .
is located predominantly in the:
A. Outer membrane of the mitochondria
B. Intermembrane space of the mitochondria .
consists of several molecules (primarily proteins) built into the inner membrane of a mitochondrion.
Electrons released from food are shuttled by NADH to the "top" higher-energy end of the chain.
At the "bottom" lower-energy end, oxygen captures the electrons along with H+ to form water.
Complex I/NADH dehydrogenase
Complex II/Succinate dehydrogenase
Complex III/Coenzyme Q - cytochrome c reductase
Complex IV/Cytochrome c oxidase .
the final stage of respiration where high energy electrons and hydrogen ions are used to synthesise ATP
an organism is unique to a defined ecological or geographical location such as an island, nation or other zone, or habitat.
, ETC, or simply electron transport), is any series of protein complexes and lipid-soluable messengers that convert the reductive potential of energized electrons into a cross-membrane proton gradient.
The chloroplasts then transfer this energy through electrons to other protein complexes (read: several proteins stuck together). This group of proteins is called the
Theory (5,120 views)
Carbohydrate (5,118 views)
Pyruvate (5,068 views)
Habitat (5,061 views)
Cell wall (5,028 views)
Spindle fiber (4,982 views)
Decomposer (4,975 views)
Inoculation (4,966 views) .
The purple bacteria evolved oxygen respiration by reversing the flow of molecules through their carbon fixing pathways and modifying their
s. Purple bacteria also enabled the eukaryotic lineage to become aerobic.
The energy for the pumping comes from the coupled oxidation-reduction reactions in the
. Electrons are passed from one membrane-bound enzyme to another, losing some energy with each tansfer (as per the second law of thermodynamics).
The movement of electrons along the
powers pumps that move protons into the space between the two mitochondrial membranes.
The respiratory chain, or the
, is performed by protein systems located in the inner membrane of the mitochondria. Energized electrons of hydrogen atoms transported by NADH₂ਊnd FADH₂ਊre the products of the preceding phases which are used in the respiratory chain.
The citric acid cycle, also known as the Krebs cycle, is involved in cell respiration and produces NADH and FADH2 for the
, so that is not its main purpose.
A catabolic process that makes a limited amount of ATP from glucose without an
and that produces a characteristic end-product, such as ethyl alcohol or lactic acid.
The union of haploid gametes to produce a diploid zygote.
fermentation A catabolic process that produces a characteristic product such as lactic acid or ethanol. Without an
, fermentation makes a limited amount of ATP from glucose. See: respiration.
Terminal Electron Acceptor: The last acceptor of the electron, as it exits the
Thermocline: That point in a lake, where there is a drastic drop in temperature with increase in depth.
Thermophile: An organism that grows best at temperatures around 45 and 80 ºCelsius.
The process in which glucose is converted into CO2 and H2O in the presence of oxygen, releasing large amounts of ATP. This process includes the krebs cycle,
This week we learned about NAD+ and the electron transport chain. On Tuesday we took notes most of the time. In cellular respiration, glucose and other organic molecules are broken down in a series of steps. Electrons from organic compounds are usually first transferred to NAD+, a coenzyme. As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration. NADH passes the electrons to the electron transport chain. Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction. Oxygen pulls electrons down the chain in an energy-yielding tumble. The energy yielded is then used to regenerate ATP. We also learned about the stages of cellular respiration. The first stage is glycolysis, which breaks down glucose into two molecules of pyruvate. Secondly, Pyruvate oxidation and the citric acid cycle completes the breakdown of glucose. The last step is oxidative phosphorylation, which accounts for most of ATP synthesis. Oxidative phosphorylation generates most ATP because of redox reactions. A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation. For each molecule of glucose degraded to carbon dioxide and water by respiration, the cell makes up to 32 molecules of ATP. Glycolysis itself occurs in the cytoplasm and has two phases: energy investment and energy payoff. Glycolysis occurs whether or not oxygen is present. All of this info is somewhat unclear and confusing to me.
On Friday, the day of finals, we finished taking notes. We learned about the pathway of the electron transport. The electron transport chain is in the inner membrane of the mitochondrion. Most of the chain’s components are proteins, which exist in multi-protein complexes. The carriers alternate reduced and oxidized states as they accept and donate electrons. Electrons drop in free energy as they go down the chain and are finally passed to oxygen, forming water. Electrons are transferred from NADH or FADH2 to the electron transport chain. Electrons are passed through a number of proteins including cytochromes to oxygen. The electron transport chain generates no ATP directly. It breaks the large free-energy drop from food to oxygen into smaller steps that release free energy in manageable amounts. We also did a lab on Friday about people who had died in a very similar way. People who lived in the same area had all taken Tylenol, passed out, and died. We learned that taking too much Tylenol blocks part of your electron transport pathway, causing it to not work correctly. The body is then producing a lot of NADH that cannot turn into NAD+. It cannot turn into NAD+ because the electrons are getting piled up in the pathway. Essentially, the victims died of suffocation. The lab was very interesting and brought what we learned to life, which made it easier to understand.
ELECTRON TRANSPORT CHAIN
The collection of electron carrier molecules embedded in the inner membrane Of the mitochondrion is called electron transport chain. – I – he folding of the inner membrane forms cristae. These cristae contains electron carrier in the form ()I prosthetic groups. Prosthetic groups are Lightly bound to molecules of proteins. The prosthetic groups are non protein components. These prosthetic groups alternate between reduced and oxidized states during electron transport chain. They accept and donate electrons. There are following steps of electron transport chain:
I. NADH to FMN: Electrons are removed from food during glycolysis and the Krebs cycle. These electrons form NADH,. NADI 4, transfers the electrons to flavoproteil• Flavoprotein is the first molecule of electron transport chain. The flavoprotein has a prosthetic group called mononucleotide (WN).
- FMN to Fe.S: The FMN passes electrons to an iron-sulfur protein (Fe-S). It is one of a family of proteins in which both iron and sulfur tightly bound. It is a redox reaction. The FMN returns to its oxidized form.
- Fe.S to Ubiquinone (Q): The iron protein then passes the electrons to a compound ubiquinone. This electron carrier is-the only member of the electron transport chain that is not a protein. A molecule of ATP is synthesized during this transfer.
- Ubiquinone to Cytochromes: Most of the remaining electron carriers between 0 and oxygen are proteins called cytochromes.Their prosthetic group is called haem group. Haem group is an organic ring. It is surrounded by a single iron atom. The electron chain has several types of cytochromes. Each group has a different protein with a haem group. These are:
- Cytochrome b
- Cytochrome c
- Cytochrome a
- Cytochrome a3
FADH2 an alternate source of electron
Another source of electrons for the transport chain is FADI12. It is produced during Krebs cycle. FADH, adds its electrons to transport chain at a lower energy level than that of NADH. Therefore, the electron transport chain provides about one third less energy than FADH,. The electron transport chain makes no ATP directly. Its function is to pass electrons from food to oxygen. It breaks a large free energy drop into a series of smaller steps that release energy in manageable amounts. Mitochondria synthesize ATP during a mechanism called chemiosmosis.
Oxidative Phosphorylation and ATP Yield
Recall, substrate-level phosphorylation was introduced in Tutorial 22. The generation of ATP from chemiosmosis is referred to as oxidative phosphorylation because oxygen's oxidative property allows a large amount of free energy to be made available for ATP synthesis.
This figure emphasizes several important concepts about cellular respiration. First, note the locations of glycolysis, the Krebs cycle, and the electron transport chain and oxidative phosphorylation. Second, note how the electron carriers transport electrons to the transport chain, and the net amount of ATP generated at each step. In particular, compare the amount of ATP generated by oxidative phosphorylation to the amount generated by substrate-level phosphorylation. The maximum net yield of 38 ATPs per molecule of glucose is merely an estimate. Much of the energy bound in a molecule of glucose is actually lost as heat during metabolism. While this heat is actually a waste product, homeotherms ("warm-blooded" animals) capitalize on this waste and use it to maintain constant body temperatures.
Figure 5. An Overview of Cellular Respiration. (Click to enlarge)
Electron Transport Chain
Introduction/Background: In Jennifer Osterhage's Introductory Biology I taught at the University of Kentucky, she taught the concepts involved in the electron transport chain using a fun, interactive activity with clickers and student volunteers.
Goal/s: The goals of this activity are to understand the electron transport chain and the effect of perturbations on the system.
Class: BIO148: Introductory Biology I
- First, students must listen to a mini-lecture about cellular respiration.
- The activity takes place in two parts:
- Students looked at data from "autopsies" from the tylenol murders in 1982 (adapted from Buffalo case study). Clicker questions asked what was the direct target of the poison in the tylenol. Was glycolysis the direct target, etc?
- After a discussion that the target must be part of the electron transport chain (ETC), the instructor asked student volunteers to come up and act as members of the chain. Tennis balls were electrons. Electrons were passed from NADH and FADH2 to members of the complex.
Follow-up: Formative assessment built into the activity with clicker questions throughout. There was a quiz over the material the next class.
Comments: Students liked analyzing the autopsy data and like being able to visualize the ETC by acting it out.
Materials/Resources: Clickers student volunteers held sheets to act as members of the electron transport chain
Research output : Thesis › internal PhD, WU
T1 - Electron transport chains of lactic acid bacteria
N2 - Lactic acid bacteria are generally considered facultative anaerobic obligate fermentative bacteria. They are unable to synthesize heme. Some lactic acid bacteria are unable to form menaquinone as well. Both these components are cofactors of respiratory (electron transport) chains of prokaryotic bacteria. Lactococcus lactis, and several other lactic acid bacteria, however respond to the addition of heme in aerobic growth conditions. This response includes increased biomass and robustness. In this study we demonstrate that heme-grown Lactococcus lactis in fact do have a functional electron transport chain that is capable of generating a proton motive force in the presence of oxygen. In other words, heme addition induces respiration in Lactococcus lactis. This aerobic electron transport chain contains a NADH-dehydrogenase, a menaquinone-pool and a bd-type cytochrome. A phenotypic and genotypic screening revealed a similar response, induced by heme (and menaquinone) supplementation, in other lactic acid bacteria. The genome of Lactobacillus plantarum WCFS1 was predicted to encode a nitrate reductase A complex. We have found that Lactobacillus plantarum is capable of using nitrate as terminal electron acceptor, when heme and menaquinone are provided. Nitrate can be used by Lactobacillus plantarum as effective electron sink and allows growth on a extended range of substrates. The impact of both the aerobic and anaerobic electron transport chain, on the metabolism and global transcriptome of Lactobacillus plantarum were studied in detail. This work has resulted in the discovery of novel electron transport chains and respiratory capabilities of lactic acid bacteria. The potential respiratory capabilities of other, previously considered (strictly) anaerobic prokaryotic bacteria, were reviewed.
AB - Lactic acid bacteria are generally considered facultative anaerobic obligate fermentative bacteria. They are unable to synthesize heme. Some lactic acid bacteria are unable to form menaquinone as well. Both these components are cofactors of respiratory (electron transport) chains of prokaryotic bacteria. Lactococcus lactis, and several other lactic acid bacteria, however respond to the addition of heme in aerobic growth conditions. This response includes increased biomass and robustness. In this study we demonstrate that heme-grown Lactococcus lactis in fact do have a functional electron transport chain that is capable of generating a proton motive force in the presence of oxygen. In other words, heme addition induces respiration in Lactococcus lactis. This aerobic electron transport chain contains a NADH-dehydrogenase, a menaquinone-pool and a bd-type cytochrome. A phenotypic and genotypic screening revealed a similar response, induced by heme (and menaquinone) supplementation, in other lactic acid bacteria. The genome of Lactobacillus plantarum WCFS1 was predicted to encode a nitrate reductase A complex. We have found that Lactobacillus plantarum is capable of using nitrate as terminal electron acceptor, when heme and menaquinone are provided. Nitrate can be used by Lactobacillus plantarum as effective electron sink and allows growth on a extended range of substrates. The impact of both the aerobic and anaerobic electron transport chain, on the metabolism and global transcriptome of Lactobacillus plantarum were studied in detail. This work has resulted in the discovery of novel electron transport chains and respiratory capabilities of lactic acid bacteria. The potential respiratory capabilities of other, previously considered (strictly) anaerobic prokaryotic bacteria, were reviewed.
What is the input/output of the Electron Transport Chain?
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You have to understand that the electron transport chain will be able to yield three ATP molecules. The input of the electron transport chain is going to be NADH+FADH2. This is where the ATP will start. This will end with 34 or 36 ATP.
The electron transport chain is known to be a series of complex procedures that will make sure that electrons (electron donors and electron acceptors) will go through reduction and oxidation. This will make sure that the body will be getting enough proteins.
There are some that would need more protein as compared to the others. Take note that ATP, the end product, is used for metabolic processes.
The input and output of the electron transport chain are NADH + FADH2 for the input, and 34 or 36 ATP for the output. The electron transport chain is the last stage of cellular respiration. Electron Transport Chain can be abbreviated into ETC sometimes. You can find the ETC inside the mitochondrion.
It is an aerobic process, which means that it needs the energy to perform its functions. This transport chain of electron takes place in the cristae of the mitochondria's inner membrane. In this particular step of cellular respiration, NADH and FADH2 carry electrons and drop them off from the citric acid cycle.
When the electrons are dropped off, it gives a chance for the formation of a large amount of ATP molecules. As a matter of fact, 34 ATP is definitely produced. The electron transport chain converts oxygen directly to water after usage, which shows that it is directly aerobic.
Watch the video: Electron Transport Chain Oxidative Phosphorylation (January 2022).