Introduction: TCA cycle and Electron Transport System
A series of chemical reactions that occur in the cells of all aerobic organisms to release ATP-retained energy by converting Acetyl CoA into carbohydrates, fats, and proteins is defined as a TCA or Tricarboxylic Acid Cycle cycle. It is also known as the Citric Acid cycle and occurs in the mitochondria in the second phase of cellular respiration. Soluble enzymes cause reactions in the TCA cycle.
It is a common anaerobic regimen that provides NADH and FADH2. Each of these processes its own electrons in the following path that leads to oxidation. Without an electron, oxidation transfer will not occur. The TCA Cycle directly produces small amounts of ATP or energy molecules. It is also a cyclic method because the final step regenerates the first molecules of the path thus making it a closed loop. Occurs when there is oxygen.
The TCA or Tricarboxylic Cycle cycle is also known as the Krebs Cycle or Citric Acid Cycle. It is the second stage of cellular respiration that occurs in the mitochondrial matrix. All the enzymes involved in the citric acid cycle are dissolved.
The TCA cycle is a set of eight improved reactions and eight mediators that break down hydrocarbon substrates into carbon dioxide and water using the energy released to convert nicotinamide adenine dinucleotide from NAD + to NADH or flavin. adenine dinucleotide goes from FADH to FADH. FADH2.Succinate → fumarate: (FADH2)
It is an aerobic method because NADH and FADH2 are produced to transfer their electrons to a path that will use oxygen. When electron transfer does not occur, no oxidation occurs. Very little ATP is produced during the process directly.
The TCA cycle is a closed-loop. The final step of the process renews the first molecule of the method.
- Why Is The TCA Cycle Also Called The Krebs Cycle?
The TCA Cycle or Citric Acid cycle was proposed by British biochemist Sir Hans Adolf Krebs. Krebs clarified much of the reaction in this approach and gained recognition for his work. In addition, Fritz Lipmann and Nathan Kaplan discovered Coenzyme A which later allowed other researchers to perform a complete cycle as we know it today.
Steps of the TCA Cycle:
The TCA cycle is an eight-step process that plays a major role in atomic fragmentation. Macromolecules such as glucose, sugar, fatty acids, amino acids, etc. cannot directly enter the TCA cycle. Therefore, they begin to break down into two acetyls Acetyl CoA. After Acetyl CoA enters the TCA cycles, it undergoes another chemical reaction to produce carbon dioxide and energy. Each step of the process is processed by a soluble enzyme.
Pyruvate derived from glucose undergoes oxidation to provide acetyl CoA. So Acetyl CoA enters the cycle and follows a series of reactions:
- Step 1: Acetyl-CoA, a combination of two carbon molecules, combines with a four-carbon compound, oxaloacetate, which leads to the formation of a six-carbon molecule called citrate and produces a CoA group.
- Step 2: In the next step, the citrate is converted to an isomer of citrate and isocitrate. Two processes occur simultaneously in this step. Initially, citrate loses its water molecule and also gains isocitrate.
- Step 3: The third stage of isocitrate oxidation occurs. A five-carbon molecule called ɑ-ketoglutarate is released after the release of a carbon dioxide molecule. NAD + has also been reduced to NADH. This step is processed by the enzyme isocitrate dehydrogenase.
- Step 4: In this process, ɑ-ketoglutarate oxidized releases the carbon dioxide molecule, and lowers NAD + into NADH. At the same time, CoA is replaced by the remaining four-carbon molecules that make up Succinyl CoA, an unstable compound. This step is processed by the enzyme ɑ-ketoglutarate.
- Step 5: The phosphate group replaces CoA with succinyl CoA. It is then transferred to ADP to supply the ATP molecule. This step also provides a carbon-Succinate molecule.
- Step 6: At this point, Succinate is oxidized to give off fumarate. Also, two hydrogen atoms are transferred to FAD leading to FADH2. FADH2 then transfers its electrons directly to the electron transport chain (ETC) as the enzyme that triggers this reaction is embedded in the inner membrane of mitochondria.
- Step 7: The water molecule is added to the fumarate and the fumarate is converted to malate with the help of the enzyme Fumarase.
- Step 8: At this stage of the cycle, oxidation of malate stimulates oxaloacetate which is a compound of four carbon, and another NAD + molecule is reduced to NADH. This step is processed by the enzyme Malate Dehydrogenase.
End TCA Cycle Products
One cycle of Citric Acid produces the following final products-
- Two carbon dioxide molecules
- Three NADH molecules, three hydrogen ions, one FADH₂ molecule
- One GTP molecule
Electron Transport System:
The electron transport system (ETS) is a major component of the energy-producing process known as cellular respiration. This system is responsible for the production of ATP, a molecule that serves as the energy currency of the cell. The ETS is composed of a series of proteins, lipids, and enzymes that shuttle electrons along a series of redox reactions, ultimately resulting in the formation of ATP.
The first component of the ETS is the electron donor, which is usually a molecule like NADH or FADH2. These molecules donate electrons to the ETS, allowing it to continue the redox reactions. The electrons are then passed through a series of electron carriers, including cytochrome complexes and quinones, which transfer the electrons to the next component in the system.
Once the electrons reach the electron acceptor, usually oxygen, they are used to reduce the acceptor molecule. This reduction creates a proton gradient, which is used to drive ATP synthesis through the ATP synthase enzyme. The ATP synthase enzyme then combines ADP and phosphate to form ATP, which is then used to fuel cellular processes.
The ETS is a vital component of cellular respiration, as it is responsible for the production of ATP. Without the ETS, cells would not be able to effectively produce energy, leading to a decrease in the cell’s ability to perform its necessary functions. It is therefore important to understand how the ETS works in order to better understand how cells generate energy and carry out their vital functions.
Summary of the Whole Cycle:
Two carbon molecules enter the acetyl CoA pathway, and two carbon dioxide molecules are released. Three NADH molecules, three hydrogen ions, one FADH₂ molecule is produced, and one ATP molecule.
It should be noted that one glucose molecule produces two Acetyl CoA molecules. Therefore, the number of final products is doubled.
Also read: Concept of Elements, Atoms, and Molecules
Question 1: What is the Importance of the TCA Cycle?
Answer 1: Although ATP produced directly in one TCA cycle is very small (2 ATP molecules per cycle), it participates in the release of many ATP atoms indirectly with the help of NADH and FADH2 produced in a cycle. Both of these are electron carriers and attach their electrons to the electron transport chain (ETC) to drive ATP molecules through oxidative phosphorylation. The TCA cycle acts as the last oxidative mechanism of degradation of carbohydrates, proteins, lipids, amino acids, via Acetyl CoA, or other intermediate cycles.
Question 2: Why is the TCA Cycle an Amphibolic Approach?
Answer 2: The amphibolic pathway is the most active as a catabolic as well as the anabolic pathway. In the TCA cycle, Coenzyme A Reaction with anabolic citrate is an anabolic pathway and additional steps follow the catabolic pathway. The TCA cycle is therefore called the Amphibolic pathway.