[Biology Class Notes] on Electron Transport Chain Pdf

The steps in the respiratory process are to generate and use NADH+H+ and FADH2 stored energy. This is done when they are oxidized by the electron transport system, and the electrons are delivered to O2 resulting in H2O creation. The biochemical path the electron is traveling from one carrier to another is called the electron transport network.

What is the Electron Transport Chain?

The electron transportation chain is the last aerobic respiration portion and is the only part of the glucose metabolism that uses atmospheric oxygen. Oxygen continuously passes through plants; it enters the body via the respiratory system of animals.

Electron transport is a sequence of redox reactions that mimic a relay race or bucket brigade in which electrons are easily transported from one part to the end point of the chain where the electrons decrease molecular oxygen and produce water.

There are four protein-composed electron transport chain complexes, labelled I through IV in the electron transport chain diagram below, and the assembly of these four complexes together with related active, accessory electron carriers is described named the electron transport chain. The electron transport chain is present in multiple copies in the eukaryote inner mitochondrial membrane and in the prokaryote plasma membrane. 

But note that the prokaryote electron transport chain may not require oxygen as some live-in anaerobic conditions. All electron transport chains are commonly characterized by the presence of a proton pump to create a proton gradient across a membrane.

Below electron transport system diagram illustrates the electron transport system in mitochondria.

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Complex I

Aboard NADH, two electrons are transported to the first complex. Complex I consists of flavin mononucleotide (FMN) and the iron-sulfur (Fe-S) enzyme. FMN, originating from vitamin B2 (also known as riboflavin), is one of several prosthetic classes or co – factors in the chain of electron transport.

 

A prosthetic group is a molecule that is not protein required for a protein ‘s activity. Prosthetic groups may be organic or inorganic, and are non-peptide molecules bound to a protein that promotes their work.

Prosthetic groups include coenzymes that are the enzyme prosthetic groups. NADH dehydrogenase is the enzyme in complex I, a very large protein containing 45 chains of amino acids. Complex I can pump four hydrogen ions into the intermembrane space across the membrane from the matrix; this is how the gradient of hydrogen ions is established and maintained between the two compartments separated by the inner mitochondrial membrane.

Q and Complex II

Complex II receives FADH2 directly, which does not traverse complex I. The compound which connects the first and second complexes to the third complex is ubiquinone (Q). The Q molecule is lipid soluble, and moves freely through the membrane’s hydrophobic core. On reduction to QH2, ubiquinone transfers the electrons to the next complex in the electron transport chain.

Q derives the NADH derived electrons from complex I and the FADH2 derived electrons from complex II, like succinate dehydrogenase. This enzyme and FADH2 form a small complex that directly supplies electrons to the electron transmission chain, bypassing the first complex.

 

Since these electrons circumvent the proton pump in the first complex and thus do not energize, less ATP molecules are made from the FADH2 electrons. Basically, the amount of ATP molecules produced is directly proportional to the number of protons pumped through the mitochondrial membrane inside.

Complex III

The third complex comprises cytochrome b, another Fe-S protein, cytochrome c proteins, Rieske center (2Fe-2S center) and this complex is also known as cytochrome oxidoreductase.

Cytochrome proteins have a group of prosthetic hemes. The heme molecule of hemoglobin is similar to the heme because it includes electrons rather than oxygen. These lowers and oxidizes the iron ion at its center as it moves through the electrons, fluctuating between different oxidation states: Fe2 + (reduced) and Fe3 + (oxidized).

Because of the effects of the different proteins linking them, the heme molecules in the cytochromes have slightly different characteristics which makes each group. Complex III pushes protons through the membrane and transfers their electrons to cytochrome c for transportation to the fourth protein and enzyme complex. Cytochrome c is the accepter of Q electrons; while Q holds pairs of electrons, cytochrome c can accept only one at a tim

Complex IV

The fourth complex consists of the cytochrome c, a, and a3 proteins. This complex contains two classes of hemes (one in each cytochrome a and a3) and three ions of copper (a pair of CuA and one CuB in cytochrome a3).

The cytochromes hold a molecule of oxygen very tightly between the iron and copper ions until the oxygen is reduced altogether. The reduced oxygen then picks up two hydrogen ions to produce water (H2O) from the surrounding medium. Deleting the hydrogen ions from the system also contributes to the ion gradient used in the chemiosmosis process.

Mitochondria

Mitochondria are membrane-bound organelles with two distinct membranes. That’s rather extraordinary for an intercellular organelle. Those membranes support mitochondria’s primary job, which is to generate energy. Chemicals within the cell must go through pathways or be changed in order to generate energy. Because phosphate is a high-energy bond that supplies energy for other processes within the cell, the process of conversion creates energy in the form of ATP. As a result, the mitochondria’s prime objective is to produce energy. Because certain cells require more energy, they contain various numbers of mitochondria. Muscle, for example, contains a lot of mitochondria, as does the liver, kidney, and, to some extent, the brain, which runs on the energy produced by those mitochondria. So if you have a deficiency in the paths that the mitochondria normally use, you’ll get symptoms in the muscle, the brain, and perhaps the kidneys; a wide range of symptoms. And we’re probably not aware of all of the illnesses caused by the mitochondrial malfunction.

Mitochondrial Diseases

Mitochondrial diseases are situations in which the mitochondria are unable to execute their basic role of creating energy. Because they are predominantly hereditary disorders, you may inherit the mitochondrial dysfunction gene from one of your parents. When mitochondria fail to work normally, cells do not receive energy. As a result, the ce
lls do not operate properly. Symptoms of mitochondrial illness vary widely depending on the organ involved, and may include:

• Loss of muscle coordination

• Muscle weakness

• Muscle pain

• Exercise intolerance

• Problems with vision

• Hearing issues

• Learning disabilities

• Heart disease

• Liver disease

• Kidney disease

• Gastrointestinal problems

• Neurological problems

• Poor growth

• Delays in development

• Increased risk of infection

• Movement disorders

• Thyroid problems

• Difficulty breathing

• Memory issues

Treatment of Mitochondrial Disease

There is currently no treatment for mitochondrial disorders. Treatment, on the other hand, can help reduce symptoms and enhance the quality of life. Supportive treatment, which may include dietary control, exercise, and/or vitamin or amino acid supplements, is used to treat mitochondrial illness. Treatment differs from patient to patient and is determined by the kind of mitochondrial illness detected as well as its severity. However, it is impossible to foresee how a patient will respond to therapy or how the condition will affect that individual in the long run. Even if they have the same ailment, no two people will respond to the same treatment in the same manner. Treatments for a mitochondrial disease may include the following:

Vitamins and Supplements

Exercise

Supportive therapy such as Speech Therapy, Respiratory Therapy, Physical Therapy

Reverse Electron Flow

Reverse electron flow (also known as reverse electron transport) is a microbial metabolic method. The transmission of electrons via the electron transport chain via reverse redox processes is known as reverse electron flow. This can decrease the oxidized forms of electron donors by demanding a substantial amount of energy. Reverse electron flow has been found to be induced by a number of causes. However, further research is needed to corroborate this. Blockage of ATP synthase, for example, causes a build-up of protons and hence a larger proton-motive force, resulting in reverse electron flow.

Is the ETS a sequence?

The ETS was formerly shown as a chain, with one complex fixed in place relative to the next until the invention of the fluid mosaic model of membranes. While the complexes create ‘islands’ in the fluid membrane, it is now acknowledged that they move independently of one another and exchange electrons when they are in close proximity. The ETS is always depicted in textbooks as a physical sequence of complexes and carriers. This has the unintended consequence of conveying that they’re all attached to their places. Membranes’ fluid nature allows for electron exchange in a test tube containing membrane fragments. The presence of ETS complexes on the inner membrane has two important implications. The possibility of carriers making an exchange is substantially higher while they are floating in two-dimensional space than when they are in solution in the matrix’s three-dimensional space. They have restricted mobility and are exposed to the matrix side of the membrane for access to succinate and NADH. Second, because the ETS is located on the inner membrane, they can create a chemiosmotic gradient.