When acetyl-CoA is oxidised to form carbon dioxide and coenzymes are reduced, the Krebs cycle, also known as the Citric acid cycle, occurs in the mitochondrial matrix. This series of enzyme-catalyzed reactions occurs in the mitochondrial matrix and is responsible for the generation of ATP in the electron transport chain.
The Krebs cycle was named after Hans Krebs, who proposed the detailed cycle and was the first to propose it. In 1953, he was awarded the Nobel Prize for his contribution to science.
In an eight-step process, the acetyl group of acetyl-CoA is oxidised to create two molecules of CO₂, and the process is repeated eight times.
One ATP is created as a result of this process. NADH and FADH₂ are high-energy molecules that have been reduced.
In addition, they are manufactured.Because each glucose molecule produces two molecules of acetyl-CoA, two cycles of the Krebs cycle are required, resulting in the production of four CO₂molecules six NADH, two FADH₂, and two ATPs are present.
The Krebs Cycle
It is a catabolic reaction that takes place within the cells that we call cellular respiration. Nutrients are broken down to generate energy, which is then stored in the form of ATP, while waste products are released throughout this biochemical reaction. The process of aerobic respiration necessitates the use of oxygen.
The process of cellular respiration is divided into four stages. Glycogen is converted to carbon dioxide, and oxygen is converted to water as a result of this reaction. The ATPs are responsible for storing the energy released during the process. Each glucose molecule yields 36 to 38 ATPs, depending on the concentration.
The Four Stages are as follows:
1.Glycolysis is the partial oxidation of a glucose molecule that results in the formation of two molecules of pyruvate. The cytosol is the location where this process takes place.
2.Acetyl CoA is generated when pyruvate, which is produced during glycolysis, enters the mitochondrial matrix. It goes through an oxidative decarboxylation reaction, resulting in the formation of two molecules of Acetyl CoA. The enzyme pyruvate dehydrogenase is responsible for catalysing the reaction.
2Pyruvate + 2NAO⁻+2CoA −→ Pyruvatedehydrogenase2AcetylCoA + 2NADH + C02
3.Krebs Cycle (also known as the TCA cycle or the Citric Acid Cycle): When carbohydrates, proteins, and lipids are converted to acetyl coenzyme A or other intermediates of the cycle, this is the prevalent pathway for full oxidation of those substances by the body. It is the Tricarboxylic acid cycle or the Citric acid cycle that uses the Acetyl CoA that is created. Glucose undergoes complete oxidation during this procedure. Citrate is formed when the acetyl CoA interacts with the oxaloacetate (4C) (6C). In this process, two molecules of CO₂ are produced.
Oxaloacetate is recycled after it has been released. ATP and other high-energy compounds such as NADH and FADH₂ serve as energy storage molecules.
4.The Electron Transport System and Oxidative Phosphorylation: ATP is produced when electrons are transported from energy-dense molecules like NADH and FADH₂ to less energy-dense molecules such as ATP molecular oxygen is created through the glycolysis, citric acid cycle, and fatty acid oxidation processes by a series of electron carriers. O2 is reduced to the element H₂O.It takes place within the inner membrane of the mitochondrial membrane.
Steps in the Krebs Cycle
There are eight steps in the process. The Krebs cycle occurs in the matrix of mitochondria when the cells are subjected to aerobic circumstances.
Step 1: The condensation of acetyl CoA with oxaloacetate (4C) results in the formation of citrate (6C), which results in the release of coenzyme A. The enzyme citrate synthase is responsible for catalysing the reaction.
Step 2: Isocitrate is formed by converting citrate to its isomer. The enzyme aconitase is responsible for catalysing this reaction.
Step 3: Isocitrate is dehydrogenated and decarboxylated to generate -ketoglutarate, which is the final product (5C). CO₂ in its molecular form
is made available. The enzyme isocitrate dehydrogenase is responsible for catalysing the reaction. It is an enzyme that requires NAD+ to function. NAD⁺ is transformed to NADH in the body.
Step 4: The oxidative decarboxylation of -ketoglutarate (5C) results in the formation of succinyl CoA. (4C). The enzyme complex including -ketoglutarate dehydrogenase is responsible for catalysing the process. One molecule of carbon dioxide
NAD+ is transformed to NADH after it has been released.
Stage 5 :- By the enzyme succinyl CoA synthetase, succinyl CoA is transformed to succinate in the fifth and final step. This is followed by the phosphorylation of GDP at the level of the substrate to produce GTP. GTP transfers its phosphate to ADP, resulting in the formation of ATP.
Step 6:- The enzyme succinate dehydrogenase catalyses the oxidation of succinate to fumarate in FAD is transformed to FADH₂ as a result of this mechanism.
Step 7.:-Fumarate is changed to malate by the addition of one liter of water
Fumarase is the enzyme that is responsible for this process.
After being dehydrogenated to generate oxaloacetate, malate is combined with another acetyl CoA molecule to kick-start the new cycle in Step 8. The hydrogens that are removed are transferred to NAD+, resulting in the formation of NADH. The enzyme malate dehydrogenase is responsible for catalysing the reaction.
Summary of the Krebs Cycle
The Krebs cycle happens in the mitochondrial matrix, which is where it is named.
- Acetyl CoA, which is produced from the end result of glycolysis, pyruvate, and it condenses with 4 carbon oxaloacetate, which is generated back in the Krebs cycle, are the reactants in the Krebs cycle
- Krebs Cycle Products are substances that are produced during the Krebs cycle
- Each citric acid cycle results in the formation of the following products:
- CO₂ is made up of two molecules and CO₂ emissions are being reduced
- In the case of citric acid, decarboxylation takes happen in two places
- Isocitrate (6C) is converted to -ketoglutarate during the process (5C)
- Succinyl CoA is formed during the conversion of -ketoglutarate (5C) (4C)
- The conversion of succinyl CoA to succinate results in the production of one ATP.
- Three NAD+ atoms are reduced to NADH, while one FAD+ atom is transformed into FADH₂ as evidenced by the following reactions:
- Isocitrate is converted to -ketoglutarate, which is then converted to NADH.
- Succinyl CoA is converted to NADH by -ketoglutarate.
- FADH₂ is formed when succinate is converted to fumarate.
- NADH is formed when malate is converted to oxaloacetate.
- It should be noted that two molecules of Acetyl CoA are created from the oxidative decarboxylation of two pyruvates, implying that two cycles are necessary for each glucose molecule to be converted.
- To summarise, the Krebs cycle produces 4CO2, 6 NADH, and 2 FADH₂ when a glucose molecule undergoes complete oxidation. as well as two ATPs
- On oxidation in the electron transport chain, each molecule of NADH can create 2-3 ATPs, while each molecule of FADH₂ can form 2 ATPs.
CONCLUSION
The Krebs cycle, also known as the citric acid cycle, is a series of events that take place in the mitochondria of living cells and are responsible for nearly all of the energy produced during aerobic respiration. It makes use of oxygen and excretes water and carbon dioxide as waste products. ADP is transformed into ATP in this step.