We already know that there are two pathways are theirs in cellular respiration namely glycolysis and cellular respiration. The main aim is to produce ATP. But most of the ATP is not produced directly from these pathways during the aerobic breakdown of glucose. The ATP is obtained from a process that starts with moving electrons through electron transporter series. That series finally underwent a series known as the electron transport chain. In matrix space, the hydrogen ions are piled up. The hydrogen ions that are accumulated in the matrix space started diffusing bypass through ATP synthase and form a concentration gradient. The catalytic action of ATP synthase takes place with the help of hydrogen ions. It phosphorylates ADP and finally, ATP is produced.
The last stage of aerobic cellular respiration is the electron transport chain that uses atmospheric oxygen in glucose metabolism. Through respiratory organs of plants and animals oxygen continuously diffuses into the cells. The electron transport chain constitutes of redox reaction series where electrons are passed from one to another component in a continuous manner, very rapidly. The electrons reduce molecular oxygen at the endpoint of the cells and produce water. These four protein complexes associate with mobile and accessory electron carriers together known as electron transport chains. In eukaryotes, inner mitochondrial membrane and prokaryotes' plasma membrane multiple electron transport chains are present. In some cases, in prokaryotic organisms, the electron transport chain does not require oxygen as some of them are living in anaerobic conditions. Generally, all the electron transport chains possess a proton pump that generates a proton gradient across a membrane.
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Proteins and other organic molecules together make the ETC. It is found in the inner membrane of mitochondria of eukaryotic cells and the plasma membrane of prokaryotic cells. The main function of ETC is described below
It produces a proton gradient. The proton gradient is stored energy that may be used to generate ATP during chemiosmosis.
It generates NAD+ and FAD which are mobile carriers. These mobile carriers are used in the two pathways of cellular respiration i.e. citric acid cycle and glycolysis.
In eukaryotic organisms, the electron transport chain reaction takes place inside the mitochondria. The mitochondrion is a membrane-bound organelle that stores energy. There are fewer or more mitochondria present inside the cells depending on how much work is done by specific cells. As the muscle cells require lots of energy to do work they have approximately thousands of mitochondria are present in their cells. Mitochondria is present in the plant cells and throughout the process of photosynthesis, they produce glucose. This glucose is used in the cellular respiration of the cells as well as the electron transport chain in mitochondria.
Along the inner membrane of mitochondria, the ETC reactions take place. The citric acid cycle takes place inside the mitochondria and generates some chemicals that are required in ETC reactions. In prokaryotic cells, the ETC reactions take place in the plasma membrane of the cells.
The four complex electron transport chains are described below
Complex I (NADH dehydrogenase) − It is a large and L-shaped structure. Its main function is to accept high-energy electrons from NADH molecules.
Complex II (succinate reductase) − It takes part in the citric acid cycle. It contains succinate dehydrogenase which is an enzyme. Complex II does not move through complex I and directly receives FADH2. Complex II can oxidize the FADH2back into FAD and move the free electrons through a series of iron-sulfur clusters.
Complex III (cytochrome oxidoreductase) − Cytochrome b and Cytochrome c protein constitute the complex III. The prosthetic group of heme is present in the cytochrome protein. The heme is almost similar to the haemoglobin. The main difference between them haemoglobin carries oxygen while heme carries electrons.
Complex IV (cytochrome oxidase) − Complex four is composed of cytochrome proteins c, a, and a3. The complex IV contains copper ions (three) and heme groups (two).
These inhibitors bind the electron transport chain as much as possible. The inhibitors of ETC are listed below
Rotenone − It is a nontoxic inhibitor of the electron transport chain. It inhibits the complex I. From Derris elliptica and Lonchoncarpus root extract, we get these compounds. Rotenone is harmless to mammals due to its poor absorption quality but fishes are affected by its toxicity.
Pieridine A − Its function is the same as rotenone. It produces by strains of streptomyces. Pieridine is used to treat infections.
Antimycin A − It is produced by streptomyces. The electrons are prevented from flowing between cytochrome b and c1. This antibiotic blocks complex III.
Cyanide − It inhibits the terminal electron transfer to oxygen, complex IV.
Carbon monoxide − It blocks cytochrome oxidase and oxygen. It inhibits irons.
The electron transport chain is a chain of protein and other organic molecules. In eukaryotic cells, the electron transport reaction takes place in mitochondria while in prokaryotes it occurs in the plasma membrane. Various compounds inhibit ETC. The inhibitors bind to the electron transport chains. These inhibitors prevented the flow of electrons in the electron transport chain and thus block the chain in three sites.
Q1. How the proton gradient is formed?
Ans. As we know that electron transport chain is organized into complexes. With the help of multiple redox reactions, the molecules transfer electrons from one another. Throughout the electron transport chain, electrons are moving from higher energy levels to lower energy levels. This reaction releases energy that is used to pump H+ ions across the inner membrane. Thus throughout the inner membrane proton gradient is formed.
Q2. What is chemiosmosis?
Ans. In the chemiosmosis process, in the series of redox reactions free energy is produced. This free energy is used to pump H+ ions across the inner membrane.
Q3. What is a redox reaction?
Ans. The Redox reaction is also known as an oxidation-reduction reaction. These reactions involve the transfer of electrons between atoms, ions, or molecules. Redox reactions occur all around us. The burning of fuels, metal corrosion, cellular respiration, and photosynthesis in plants are examples of redox reactions.
Q4. What are prokaryotic and eukaryotic cells?
Ans. Prokaryotic cells are present in unicellular organisms and do not have a membrane-bound nucleus, genetic materials are present in the cytoplasm. Bacteria are an example of prokaryotes. While eukaryotic cells are found in multicellular organisms, they have a membrane-bound nucleus. The organelles present in the eukaryotic cell perform various functions.
Q5. Write one function of the plasma membrane.
Ans. It is a semi-permeable membrane that surrounds the cell and its organelles.
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