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Carbohydrate metabolism and citric acid cycle

Carbohydrate metabolism and citric acid cycle

Therefore, vitric every Carbohydrate metabolism and citric acid cycle molecule mteabolism enters aerobic respiration, a net total jetabolism 36 ATPs are produced Figure 6. Archived PDF from the original on Metabokism metabolic pathways such Carbohydrate metabolism and citric acid cycle glycolysis, tricarboxylic acid TCAand the electron transport system, plus one enzyme, pyruvate dehydrogenase PDHallow efficient conversion of glucose chemical bond energy into useable energetic intermediates such as ATP. This lactic acid fermentation occurs in most cells of the body when oxygen is limited or mitochondria are absent or nonfunctional. Similarly, when a person exercises, muscles use ATP faster than oxygen can be delivered to them.

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KREBS CYCLE MADE EASY - Krebs cycle Simple Animation. Carbohydrate Metabolism Lesson

Carbohydrate metabolism and citric acid cycle -

The last step of glycolysis involves the dephosphorylation of the two phosphoenolpyruvate molecules by pyruvate kinase to create two pyruvate molecules and two ATP molecules. In summary, one glucose molecule breaks down into two pyruvate molecules, and creates two net ATP molecules by substrate-level phosphorylation and two NADH molecules by glycolysis.

Therefore, glycolysis generates energy for the cell and creates pyruvate molecules that can be processed further through the aerobic Krebs cycle also called the citric acid cycle or tricarboxylic acid cycle ; converted into lactic acid or alcohol in yeast by fermentation; or used later for the synthesis of glucose through gluconeogenesis.

When oxygen O 2 is limited or absent, pyruvate enters an alternate, anaerobic pathway. In these reactions, pyruvate can be converted into lactic acid. In this reaction, lactic acid replaces oxygen as the final electron acceptor. This lactic acid fermentation occurs in most cells of the body when oxygen is limited or mitochondria are absent or nonfunctional.

For example, because erythrocytes red blood cells lack mitochondria, they must produce their ATP using this same fermentation pathway.

This is an effective pathway of ATP production for short periods of time, ranging from seconds to a few minutes. The lactic acid produced diffuses into the plasma and is carried to the liver, where it is converted back into pyruvate or glucose via the Cori cycle.

Similarly, when a person exercises, muscles use ATP faster than oxygen can be delivered to them. They depend on glycolysis and lactic acid production for rapid ATP production.

The NADH and FADH 2 pass electrons on to the electron transport chain, which uses the transferred energy to produce ATP by oxidative phosphorylation. As the terminal step in the electron transport chain, oxygen is the terminal electron acceptor, combining with electrons and hydrogen ions to produce water inside the mitochondria.

The pyruvate molecules generated during glycolysis are transported across the mitochondrial membrane into the inner mitochondrial matrix, where they are metabolized by enzymes in a pathway called the Krebs cycle Figure 4.

The Krebs cycle is also commonly called the citric acid cycle or the tricarboxylic acid TCA cycle. During the Krebs cycle, high-energy molecules, including ATP, NADH, and FADH 2 , are created.

NADH and FADH 2 then pass electrons through the electron transport chain in the mitochondria to generate more ATP molecules. The three-carbon pyruvate molecule generated during glycolysis moves from the cytoplasm into the mitochondrial matrix, where it is converted by the enzyme pyruvate dehydrogenase into a two-carbon acetyl coenzyme A acetyl CoA molecule.

This reaction is an oxidative decarboxylation reaction. Acetyl CoA enters the Krebs cycle by combining with a four-carbon molecule, oxaloacetate, to form the six-carbon molecule citrate, or citric acid, at the same time releasing the coenzyme A molecule.

The six-carbon citrate molecule is systematically converted to a five-carbon molecule and then a four-carbon molecule, ending with oxaloacetate, the beginning of the cycle. Along the way, each citrate molecule will produce one ATP, one FADH 2 , and three NADH. The FADH 2 and NADH will enter the oxidative phosphorylation system located in the inner mitochondrial membrane.

In addition, the Krebs cycle supplies the starting materials to process and break down proteins and fats. To start the Krebs cycle, citrate synthase combines acetyl CoA and oxaloacetate to form a six-carbon citrate molecule; CoA is subsequently released and can combine with another pyruvate molecule to begin the cycle again.

The aconitase enzyme converts citrate into isocitrate. In two successive steps of oxidative decarboxylation, two molecules of CO 2 and two NADH molecules are produced when isocitrate dehydrogenase converts isocitrate into the five-carbon α-ketoglutarate, which is then catalyzed and converted into the four-carbon succinyl CoA by α-ketoglutarate dehydrogenase.

The enzyme succinyl CoA dehydrogenase then converts succinyl CoA into succinate and forms the high-energy molecule GTP, which transfers its energy to ADP to produce ATP by substrate-level phosphorylation.

Succinate dehydrogenase then converts succinate into fumarate, forming a molecule of FADH 2. Oxaloacetate is then ready to combine with the next acetyl CoA to start the Krebs cycle again see Figure 4.

For each turn of the cycle, three NADH, one ATP through GTP , and one FADH 2 are created. Each carbon of pyruvate is converted into CO 2 , which is released as a byproduct of oxidative aerobic respiration. The electron transport chain ETC uses the NADH and FADH 2 produced by the Krebs cycle to generate ATP.

Electrons from NADH and FADH 2 are transferred through protein complexes embedded in the inner mitochondrial membrane by a series of enzymatic reactions. In the presence of oxygen, energy is passed, stepwise, through the electron carriers to collect gradually the energy needed to attach a phosphate to ADP and produce ATP.

The role of molecular oxygen, O 2 , is as the terminal electron acceptor for the ETC. This means that once the electrons have passed through the entire ETC, they must be passed to another, separate molecule.

This is the basis for your need to breathe in oxygen. Without oxygen, electron flow through the ETC ceases. The electrons released from NADH and FADH 2 are passed along the chain by each of the carriers, which are reduced when they receive the electron and oxidized when passing it on to the next carrier.

The accumulation of these protons in the space between the membranes creates a proton gradient with respect to the mitochondrial matrix.

Also embedded in the inner mitochondrial membrane is an amazing protein pore complex called ATP synthase. This rotation enables other portions of ATP synthase to encourage ADP and P i to create ATP. In accounting for the total number of ATP produced per glucose molecule through aerobic respiration, it is important to remember the following points:.

Similarly, when a person exercises, muscles use ATP faster than oxygen can be delivered to them. They depend on glycolysis and lactic acid production for rapid ATP production.

The NADH and FADH2 pass electrons on to the electron transport chain, which uses the transferred energy to produce ATP. As the terminal step in the electron transport chain, oxygen is the terminal electron acceptor and creates water inside the mitochondria.

Figure 3. Click to view a larger image. The process of anaerobic respiration converts glucose into two lactate molecules in the absence of oxygen or within erythrocytes that lack mitochondria. During aerobic respiration, glucose is oxidized into two pyruvate molecules.

The pyruvate molecules generated during glycolysis are transported across the mitochondrial membrane into the inner mitochondrial matrix, where they are metabolized by enzymes in a pathway called the Krebs cycle Figure 4. The Krebs cycle is also commonly called the citric acid cycle or the tricarboxylic acid TCA cycle.

During the Krebs cycle, high-energy molecules, including ATP, NADH, and FADH2, are created. NADH and FADH2 then pass electrons through the electron transport chain in the mitochondria to generate more ATP molecules.

Figure 4. During the Krebs cycle, each pyruvate that is generated by glycolysis is converted into a two-carbon acetyl CoA molecule. The acetyl CoA is systematically processed through the cycle and produces high- energy NADH, FADH2, and ATP molecules.

The three-carbon pyruvate molecule generated during glycolysis moves from the cytoplasm into the mitochondrial matrix, where it is converted by the enzyme pyruvate dehydrogenase into a two-carbon acetyl coenzyme A acetyl CoA molecule.

This reaction is an oxidative decarboxylation reaction. Acetyl CoA enters the Krebs cycle by combining with a four-carbon molecule, oxaloacetate, to form the six-carbon molecule citrate, or citric acid, at the same time releasing the coenzyme A molecule.

The six-carbon citrate molecule is systematically converted to a five-carbon molecule and then a four-carbon molecule, ending with oxaloacetate, the beginning of the cycle. Along the way, each citrate molecule will produce one ATP, one FADH2, and three NADH.

The FADH2 and NADH will enter the oxidative phosphorylation system located in the inner mitochondrial membrane. In addition, the Krebs cycle supplies the starting materials to process and break down proteins and fats. To start the Krebs cycle, citrate synthase combines acetyl CoA and oxaloacetate to form a six-carbon citrate molecule; CoA is subsequently released and can combine with another pyruvate molecule to begin the cycle again.

The aconitase enzyme converts citrate into isocitrate. In two successive steps of oxidative decarboxylation, two molecules of CO2 and two NADH molecules are produced when isocitrate dehydrogenase converts isocitrate into the five-carbon α-ketoglutarate, which is then catalyzed and converted into the four-carbon succinyl CoA by α-ketoglutarate dehydrogenase.

The enzyme succinyl CoA dehydrogenase then converts succinyl CoA into succinate and forms the high-energy molecule GTP, which transfers its energy to ADP to produce ATP.

Succinate dehydrogenase then converts succinate into fumarate, forming a molecule of FADH2. Oxaloacetate is then ready to combine with the next acetyl CoA to start the Krebs cycle again see Figure 4. For each turn of the cycle, three NADH, one ATP through GTP , and one FADH2 are created.

Each carbon of pyruvate is converted into CO2, which is released as a byproduct of oxidative aerobic respiration. The electron transport chain ETC uses the NADH and FADH 2 produced by the Krebs cycle to generate ATP.

Electrons from NADH and FADH 2 are transferred through protein complexes embedded in the inner mitochondrial membrane by a series of enzymatic reactions. In the presence of oxygen, energy is passed, stepwise, through the electron carriers to collect gradually the energy needed to attach a phosphate to ADP and produce ATP.

The role of molecular oxygen, O 2 , is as the terminal electron acceptor for the ETC. This means that once the electrons have passed through the entire ETC, they must be passed to another, separate molecule. This is the basis for your need to breathe in oxygen.

Without oxygen, electron flow through the ETC ceases. Figure 5. The electrons released from NADH and FADH 2 are passed along the chain by each of the carriers, which are reduced when they receive the electron and oxidized when passing it on to the next carrier.

Each of these reactions releases a small amount. The accumulation of these protons in the space between the membranes creates a proton gradient with respect to the mitochondrial matrix. Also embedded in the inner mitochondrial membrane is an amazing protein pore complex called ATP synthase.

This rotation enables other portions of ATP synthase to encourage ADP and P i to create ATP. In accounting for the total number of ATP produced per glucose molecule through aerobic respiration, it is important to remember the following points:.

Therefore, for every glucose molecule that enters aerobic respiration, a net total of 36 ATPs are produced see Figure 6. Figure 6. Carbohydrate metabolism involves glycolysis, the Krebs cycle, and the electron transport chain. Gluconeogenesis is the synthesis of new glucose molecules from pyruvate, lactate, glycerol, or the amino acids alanine or glutamine.

This process takes place primarily in the liver during periods of low glucose, that is, under conditions of fasting, starvation, and low carbohydrate diets.

So, the question can be raised as to why the body would create something it has just spent a fair amount of effort to break down? Certain key organs, including the brain, can use only glucose as an energy source; therefore, it is essential that the body maintain a minimum blood glucose concentration.

When the blood glucose concentration falls below that certain point, new glucose is synthesized by the liver to raise the blood concentration to normal. Gluconeogenesis is not simply the reverse of glycolysis.

There are some important differences Figure 7. Pyruvate is a common starting material for gluconeogenesis. First, the pyruvate is converted into oxaloacetate. Oxaloacetate then serves as a substrate for the enzyme phosphoenolpyruvate carboxykinase PEPCK , which transforms oxaloacetate into phosphoenolpyruvate PEP.

From this step, gluconeogenesis is nearly the reverse of glycolysis. PEP is converted back into 2-phosphoglycerate, which is converted into 3-phosphoglycerate.

Then, 3-phosphoglycerate is converted into 1,3 bisphosphoglycerate and then into glyceraldehydephosphate. Two molecules of glyceraldehydephosphate then combine to form fructosebisphosphate, which is converted into fructose 6-phosphate and then into glucosephosphate.

Finally, a series of reactions generates glucose itself. In gluconeogenesis as compared to glycolysis , the enzyme hexokinase is replaced by glucosephosphatase, and the enzyme phosphofructokinase-1 is replaced by fructose-1,6-bisphosphatase. This helps the cell to regulate glycolysis and gluconeogenesis independently of each other.

As will be discussed as part of lipolysis, fats can be broken down into glycerol, which can be phosphorylated to form dihydroxyacetone phosphate or DHAP. Keywords: Carbohydrate; Gluconeogenesis; Glycogenesis; Glycogenolysis; Glycolysis; Oxidative pathway; Pentose phosphate pathway; Pyruvate decarboxylation.

Copyright © The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved. Abstract In mammals, there are different metabolic pathways in cells that break down fuel molecules to transfer their energy into high energy compounds such as adenosine-5'-triphosphate ATP , guanosine-5'-triphosphate GTP , reduced nicotinamide adenine dinucleotide NADH2 , reduced flavin adenine dinucleotide FADH2 and reduced nicotinamide adenine dinucleotide phosphate NADPH2.

Carbohydrate metabolism and citric acid cycle will consider Energize your mind and body the reverse process of photosynthesis, namely citrc carbohydrates, especially glucose, are converted to energy by cjcle broken Carbphydrate into carbon Carbohydrate metabolism and citric acid cycle and water. A general summary of the several stages Carbohyfrate is shown in Figure Initially, the storage fuels or foodstuffs fats, carbohydrates, and proteins are hydrolyzed into smaller components fatty acids and glycerol, glucose and other simple sugars, and amino acids. The structure of this compound and the manner in which fatty acids are degraded has been considered in Section Fand amino acid metabolism is discussed briefly in Section C. This section is concerned mainly with the pathway by which glucose is metabolized by the process known as glycolysis. Carbohydrate metabolism and citric acid cycle

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