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Puravive review- Puravive rice hack 2024Energy metabolism -
Essentially no carbohydrate digestion occurs in the stomach, and food particles pass through to the small intestine, where α-amylase and intestinal enzymes convert complex carbohydrate molecules starches to monosaccharides.
The monosaccharides then pass through the lining of the small intestine and into the bloodstream for transport to all body cells. Protein digestion begins in the stomach as pepsinogen in gastric juice is converted to pepsin, the enzyme that hydrolyzes peptide bonds.
The partially digested protein then passes to the small intestine, where the remainder of protein digestion takes place through the action of several enzymes. The resulting amino acids cross the intestinal wall into the blood and are carried to the liver. Lipid digestion begins in the small intestine.
Bile salts emulsify the lipid molecules, and then lipases hydrolyze them to fatty acids and monoglycerides. The hydrolysis products pass through the intestine and are repackaged for transport in the bloodstream. In cells that are operating aerobically, acetyl-CoA produced in stage II of catabolism is oxidized to carbon dioxide.
The citric acid cycle describes this oxidation, which takes place with the formation of the coenzymes reduced nicotinamide adenine dinucleotide NADH and reduced flavin adenine dinucleotide FADH 2. The sequence of reactions needed to oxidize these coenzymes and transfer the resulting electrons to oxygen is called the electron transport chain , or the respiratory chain.
The compounds responsible for this series of oxidation-reduction reactions include proteins known as cytochromes , Fe·S proteins, and other molecules that ultimately result in the reduction of molecular oxygen to water. Every time a compound with two carbon atoms is oxidized in the citric acid cycle, a respiratory chain compound accepts the electrons lost in the oxidation and so is reduced and then passes them on to the next metabolite in the chain.
Electron transport and oxidative phosphorylation are tightly coupled to each other. The enzymes and intermediates of the citric acid cycle, the electron transport chain, and oxidative phosphorylation are located in organelles called mitochondria.
Glucose is oxidized to two molecules of pyruvate through a series of reactions known as glycolysis. Some of the energy released in these reactions is conserved by the formation of ATP from ADP.
The pyruvate produced by glycolysis has several possible fates, depending on the organism and whether or not oxygen is present. In animal cells, pyruvate can be further oxidized to acetyl-CoA and then to carbon dioxide through the citric acid cycle if oxygen supplies are sufficient.
When oxygen supplies are insufficient, pyruvate is reduced to lactate. In yeast and other microorganisms, pyruvate is not converted to lactate in the absence of oxygen but instead is converted to ethanol and carbon dioxide. The amount of ATP formed by the oxidation of glucose depends on whether or not oxygen is present.
If oxygen is present, glucose is oxidized to carbon dioxide, and 36—38 ATP molecules are produced for each glucose molecule oxidized, using the combined pathways of glycolysis, the citric acid cycle, the electron transport chain, and oxidative phosphorylation. Fatty acids, released by the degradation of triglycerides and other lipids, are converted to fatty acyl-CoA, transported into the mitochondria, and oxidized by repeated cycling through a sequence of four reactions known as β - oxidation.
In each round of β-oxidation, the fatty acyl-CoA is shortened by two carbon atoms as one molecule of acetyl-CoA is formed. The remaining reactions of the citric acid cycle use the four carbon atoms of the succinyl group to resynthesize a molecule of oxaloacetate, which is the compound needed to combine with an incoming acetyl group and begin another round of the cycle.
In the fifth reaction, the energy released by the hydrolysis of the high-energy thioester bond of succinyl-CoA is used to form guanosine triphosphate GTP from guanosine diphosphate GDP and inorganic phosphate in a reaction catalyzed by succinyl-CoA synthetase.
This step is the only reaction in the citric acid cycle that directly forms a high-energy phosphate compound. GTP can readily transfer its terminal phosphate group to adenosine diphosphate ADP to generate ATP in the presence of nucleoside diphosphokinase.
Succinate dehydrogenase then catalyzes the removal of two hydrogen atoms from succinate, forming fumarate. Succinate dehydrogenase is the only enzyme of the citric acid cycle located within the inner mitochondrial membrane. We will see soon the importance of this. In the following step, a molecule of water is added to the double bond of fumarate to form L-malate in a reaction catalyzed by fumarase.
One revolution of the cycle is completed with the oxidation of L-malate to oxaloacetate, brought about by malate dehydrogenase. Oxaloacetate can accept an acetyl group from acetyl-CoA, allowing the cycle to begin again. Respiration can be defined as the process by which cells oxidize organic molecules in the presence of gaseous oxygen to produce carbon dioxide, water, and energy in the form of ATP.
We have seen that two carbon atoms enter the citric acid cycle from acetyl-CoA step 1 , and two different carbon atoms exit the cycle as carbon dioxide steps 3 and 4. Yet nowhere in our discussion of the citric acid cycle have we indicated how oxygen is used.
Oxygen is needed to reoxidize these coenzymes. Recall, too, that very little ATP is obtained directly from the citric acid cycle.
Instead, oxygen participation and significant ATP production occur subsequent to the citric acid cycle, in two pathways that are closely linked: electron transport and oxidative phosphorylation.
A cell may contain —5, mitochondria, depending on its function, and the mitochondria can reproduce themselves if the energy requirements of the cell increase. The inner membrane is extensively folded into a series of internal ridges called cristae.
Thus there are two compartments in mitochondria: the intermembrane space , which lies between the membranes, and the matrix , which lies inside the inner membrane.
The outer membrane is permeable, whereas the inner membrane is impermeable to most molecules and ions, although water, oxygen, and carbon dioxide can freely penetrate both membranes. The matrix contains all the enzymes of the citric acid cycle with the exception of succinate dehydrogenase, which is embedded in the inner membrane.
The enzymes that are needed for the reoxidation of NADH and FADH 2 and ATP production are also located in the inner membrane. They are arranged in specific positions so that they function in a manner analogous to a bucket brigade. This highly organized sequence of oxidation-reduction enzymes is known as the electron transport chain or respiratory chain An organized sequence of oxidation-reduction reactions that ultimately transports electrons to oxygen, reducing it to water.
The components of the chain are organized into four complexes designated I, II, III, and IV. Each complex contains several enzymes, other proteins, and metal ions. The metal ions can be reduced and then oxidized repeatedly as electrons are passed from one component to the next.
Recall from Chapter 5 "Introduction to Chemical Reactions" , Section 5. Electrons can enter the electron transport chain through either complex I or II.
We will look first at electrons entering at complex I. These electrons come from NADH, which is formed in three reactions of the citric acid cycle. This reaction can be divided into two half reactions:.
Oxidation half-reaction :. Reduction half-reaction :. The NADH diffuses through the matrix and is bound by complex I of the electron transport chain.
In the complex, the coenzyme flavin mononucleotide FMN accepts both electrons from NADH. Again, the reaction can be illustrated by dividing it into its respective half-reactions. Complex I contains several proteins that have iron-sulfur Fe·S centers.
The electrons that reduced FMN to FMNH 2 are now transferred to these proteins. The iron ions in the Fe·S centers are in the Fe III form at first, but by accepting an electron, each ion is reduced to the Fe II form.
Because each Fe·S center can transfer only one electron, two centers are needed to accept the two electrons that will regenerate FMN. Electrons from FADH 2 , formed in step 6 of the citric acid cycle, enter the electron transport chain through complex II.
Succinate dehydrogenase, the enzyme in the citric acid cycle that catalyzes the formation of FADH 2 from FAD is part of complex II. The electrons from FADH 2 are then transferred to an Fe·S protein.
Electrons from complexes I and II are then transferred from the Fe·S protein to coenzyme Q CoQ , a mobile electron carrier that acts as the electron shuttle between complexes I or II and complex III. Coenzyme Q is also called ubiquinone because it is ubiquitous in living systems.
Complexes III and IV include several iron-containing proteins known as cytochromes A protein that contains an iron porphyrin in which iron can alternate between Fe II and Fe III.
The iron in these enzymes is located in substructures known as iron porphyrins Figure Like the Fe·S centers, the characteristic feature of the cytochromes is the ability of their iron atoms to exist as either Fe II or Fe III. Thus, each cytochrome in its oxidized form—Fe III —can accept one electron and be reduced to the Fe II form.
This change in oxidation state is reversible, so the reduced form can donate its electron to the next cytochrome, and so on. Complex III contains cytochromes b and c, as well as Fe·S proteins, with cytochrome c acting as the electron shuttle between complex III and IV. Complex IV contains cytochromes a and a 3 in an enzyme known as cytochrome oxidase.
This enzyme has the ability to transfer electrons to molecular oxygen, the last electron acceptor in the chain of electron transport reactions. In this final step, water H 2 O is formed. Each intermediate compound in the electron transport chain is reduced by the addition of one or two electrons in one reaction and then subsequently restored to its original form by delivering the electron s to the next compound along the chain.
The successive electron transfers result in energy production. But how is this energy used for the synthesis of ATP? The process that links ATP synthesis to the operation of the electron transport chain is referred to as oxidative phosphorylation The process that links ATP synthesis to the operation of the electron transport chain.
Electron transport is tightly coupled to oxidative phosphorylation. The coenzymes NADH and FADH 2 are oxidized by the respiratory chain only if ADP is simultaneously phosphorylated to ATP.
The currently accepted model explaining how these two processes are linked is known as the chemiosmotic hypothesis , which was proposed by Peter Mitchell, resulting in Mitchell being awarded the Nobel Prize in Chemistry.
Looking again at Figure This energy comes from the electron transfer reactions in the electron transport chain.
In cells that are using energy, the turnover of ATP is very high, so these cells contain high levels of ADP. They must therefore consume large quantities of oxygen continuously, so as to have the energy necessary to phosphorylate ADP to form ATP.
Experiment has shown that 2. Two carbon atoms are fed into the citric acid cycle as acetyl-CoA. In what form are two carbon atoms removed from the cycle? What are mitochondria and what is their function in the cell? the complete oxidation of carbon atoms to carbon dioxide and the formation of a high-energy phosphate compound, energy rich reduced coenzymes NADH and FADH 2 , and metabolic intermediates for the synthesis of other compounds.
Mitochondria are small organelles with a double membrane that contain the enzymes and other molecules needed for the production of most of the ATP needed by the body. From the reactions in Exercises 1 and 2, select the equation s by number and letter in which each type of reaction occurs.
What similar role do coenzyme Q and cytochrome c serve in the electron transport chain? What is the electron acceptor at the end of the electron transport chain? To what product is this compound reduced? What is the function of the cytochromes in the electron transport chain?
Both molecules serve as electron shuttles between the complexes of the electron transport chain. Cytochromes are proteins in the electron transport chain and serve as one-electron carriers. In stage II of catabolism, the metabolic pathway known as glycolysis The metabolic pathway in which glucose is broken down to two molecules of pyruvate with the corresponding production of ATP.
converts glucose into two molecules of pyruvate a three-carbon compound with three carbon atoms with the corresponding production of adenosine triphosphate ATP. The individual reactions in glycolysis were determined during the first part of the 20th century.
It was the first metabolic pathway to be elucidated, in part because the participating enzymes are found in soluble form in the cell and are readily isolated and purified.
The pathway is structured so that the product of one enzyme-catalyzed reaction becomes the substrate of the next. The transfer of intermediates from one enzyme to the next occurs by diffusion.
The 10 reactions of glycolysis, summarized in Figure In the first 5 reactions—phase I—glucose is broken down into two molecules of glyceraldehyde 3-phosphate. In the last five reactions—phase II—each glyceraldehyde 3-phosphate is converted into pyruvate, and ATP is generated.
Notice that all the intermediates in glycolysis are phosphorylated and contain either six or three carbon atoms. When glucose enters a cell, it is immediately phosphorylated to form glucose 6-phosphate, in the first reaction of phase I. The phosphate donor in this reaction is ATP, and the enzyme—which requires magnesium ions for its activity—is hexokinase.
In this reaction, ATP is being used rather than being synthesized. The presence of such a reaction in a catabolic pathway that is supposed to generate energy may surprise you. However, in addition to activating the glucose molecule, this initial reaction is essentially irreversible, an added benefit that keeps the overall process moving in the right direction.
Furthermore, the addition of the negatively charged phosphate group prevents the intermediates formed in glycolysis from diffusing through the cell membrane, as neutral molecules such as glucose can do.
In the next reaction, phosphoglucose isomerase catalyzes the isomerization of glucose 6-phosphate to fructose 6-phosphate.
This reaction is important because it creates a primary alcohol, which can be readily phosphorylated. The subsequent phosphorylation of fructose 6-phosphate to form fructose 1,6-bisphosphate is catalyzed by phosphofructokinase , which requires magnesium ions for activity. ATP is again the phosphate donor.
When a molecule contains two phosphate groups on different carbon atoms, the convention is to use the prefix bis. When the two phosphate groups are bonded to each other on the same carbon atom for example, adenosine diphosphate [ADP] , the prefix is di.
Fructose 1,6-bisphosphate is enzymatically cleaved by aldolase to form two triose phosphates: dihydroxyacetone phosphate and glyceraldehyde 3-phosphate.
Isomerization of dihydroxyacetone phosphate into a second molecule of glyceraldehyde 3-phosphate is the final step in phase I. The enzyme catalyzing this reaction is triose phosphate isomerase. Comment : In steps 4 and 5, aldolase and triose phosphate isomerase effectively convert one molecule of fructose 1,6-bisphosphate into two molecules of glyceraldehyde 3-phosphate.
Thus, phase I of glycolysis requires energy in the form of two molecules of ATP and releases none of the energy stored in glucose. BPG has a high-energy phosphate bond see Table This phosphate group is now transferred directly to a molecule of ADP, thus forming ATP and 3-phosphoglycerate.
The enzyme that catalyzes the reaction is phosphoglycerate kinase , which, like all other kinases, requires magnesium ions to function. This is the first reaction to produce ATP in the pathway. Because the ATP is formed by a direct transfer of a phosphate group from a metabolite to ADP—that is, from one substrate to another—the process is referred to as substrate-level phosphorylation The synthesis of ATP by the direct transfer of a phosphate group from a metabolite to ADP.
In the next reaction, the phosphate group on 3-phosphoglycerate is transferred from the OH group of C3 to the OH group of C2, forming 2-phosphoglycerate in a reaction catalyzed by phosphoglyceromutase. A dehydration reaction, catalyzed by enolase , forms phosphoenolpyruvate PEP , another compound possessing a high-energy phosphate group.
The final step is irreversible and is the second reaction in which substrate-level phosphorylation occurs. The phosphate group of PEP is transferred to ADP, with one molecule of ATP being produced per molecule of PEP. The reaction is catalyzed by pyruvate kinase , which requires both magnesium and potassium ions to be active.
Comment : In phase II, two molecules of glyceraldehyde 3-phosphate are converted to two molecules of pyruvate, along with the production of four molecules of ATP and two molecules of NADH. Most of the chapter-opening essays in Chapter 16 "Carbohydrates" through Chapter 20 "Energy Metabolism" have touched on different aspects of diabetes and the role of insulin in its causation and treatment.
Although medical science has made significant progress against this disease, it continues to be a major health threat. Some of the serious complications of diabetes are as follows:. Because a person with diabetes is unable to use glucose properly, excessive quantities accumulate in the blood and the urine.
Other characteristic symptoms are constant hunger, weight loss, extreme thirst, and frequent urination because the kidneys excrete large amounts of water in an attempt to remove excess sugar from the blood.
There are two types of diabetes. In immune-mediated diabetes, insufficient amounts of insulin are produced. This type of diabetes develops early in life and is also known as Type 1 diabetes , as well as insulin-dependent or juvenile-onset diabetes.
Symptoms are rapidly reversed by the administration of insulin, and Type 1 diabetics can lead active lives provided they receive insulin as needed. Because insulin is a protein that is readily digested in the small intestine, it cannot be taken orally and must be injected at least once a day.
Researchers are still trying to find out why. Meanwhile, they have developed a simple blood test capable of predicting who will develop Type 1 diabetes several years before the disease becomes apparent.
This translates to about 16 million Americans. Type 2 diabetics usually produce sufficient amounts of insulin, but either the insulin-producing cells in the pancreas do not release enough of it, or it is not used properly because of defective insulin receptors or a lack of insulin receptors on the target cells.
In many of these people, the disease can be controlled with a combination of diet and exercise alone. For some people who are overweight, losing weight is sufficient to bring their blood sugar level into the normal range, after which medication is not required if they exercise regularly and eat wisely.
Those who require medication may use oral antidiabetic drugs that stimulate the islet cells to secrete insulin. First-generation antidiabetic drugs stimulated the release of insulin.
Newer second-generation drugs, such as glyburide, do as well, but they also increase the sensitivity of cell receptors to insulin. Some individuals with Type 2 diabetes do not produce enough insulin and thus do not respond to these oral medications; they must use insulin.
The presence or absence of oxygen determines the fates of the pyruvate and the NADH produced in glycolysis. When plenty of oxygen is available, pyruvate is completely oxidized to carbon dioxide, with the release of much greater amounts of ATP through the combined actions of the citric acid cycle, the electron transport chain, and oxidative phosphorylation.
For more information about oxidative phosphorylation, see Section However, in the absence of oxygen that is, under anaerobic conditions , the fate of pyruvate is different in different organisms.
In vertebrates, pyruvate is converted to lactate, while other organisms, such as yeast, convert pyruvate to ethanol and carbon dioxide.
These possible fates of pyruvate are summarized in Figure The net energy yield from anaerobic glucose metabolism can readily be calculated in moles of ATP.
In the initial phosphorylation of glucose step 1 , 1 mol of ATP is expended, along with another in the phosphorylation of fructose 6-phosphate step 3. In step 7, 2 mol of BPG recall that 2 mol of 1,3-BPG are formed for each mole of glucose are converted to 2 mol of 3-phosphoglycerate, and 2 mol of ATP are produced.
In step 10, 2 mol of pyruvate and 2 mol of ATP are formed per mole of glucose. For every mole of glucose degraded, 2 mol of ATP are initially consumed and 4 mol of ATP are ultimately produced.
The net production of ATP is thus 2 mol for each mole of glucose converted to lactate or ethanol. Thus anaerobic cells extract only a very small fraction of the total energy of the glucose molecule.
Contrast this result with the amount of energy obtained when glucose is completely oxidized to carbon dioxide and water through glycolysis, the citric acid cycle, the electron transport chain, and oxidative phosphorylation as summarized in Table Note the indication in the table that a variable amount of ATP is synthesized, depending on the tissue, from the NADH formed in the cytoplasm during glycolysis.
This is because NADH is not transported into the inner mitochondrial membrane where the enzymes for the electron transport chain are located. Instead, brain and muscle cells use a transport mechanism that passes electrons from the cytoplasmic NADH through the membrane to flavin adenine dinucleotide FAD molecules inside the mitochondria, forming reduced flavin adenine dinucleotide FADH 2 , which then feeds the electrons into the electron transport chain.
This route lowers the yield of ATP to 1. A more efficient transport system is found in liver, heart, and kidney cells where the formation of one cytoplasmic NADH molecule results in the formation of one mitochondrial NADH molecule, which leads to the formation of 2.
The total amount of energy conserved in the aerobic catabolism of glucose in the liver is as follows:. If we are exercising strenuously and our metabolism speeds up to provide the energy needed for muscle contraction, more heat is produced. We begin to perspire to dissipate some of that heat.
As the perspiration evaporates, the excess heat is carried away from the body by the departing water vapor. In glycolysis, how many molecules of pyruvate are produced from one molecule of glucose?
In anaerobic glycolysis, how many molecules of ATP are produced from one molecule of glucose? What coenzyme is needed as an oxidizing agent in glycolysis? How is the NADH produced in glycolysis reoxidized when oxygen supplies are limited in.
Of the total calculated in Exercise 9a, determine the number of moles of ATP produced in each process. Like glucose, the fatty acids released in the digestion of triglycerides and other lipids are broken down in a series of sequential reactions accompanied by the gradual release of usable energy.
The enzymes that participate in fatty acid catabolism are located in the mitochondria, along with the enzymes of the citric acid cycle, the electron transport chain, and oxidative phosphorylation.
This localization of enzymes in the mitochondria is of the utmost importance because it facilitates efficient utilization of energy stored in fatty acids and other molecules. Fatty acid oxidation is initiated on the outer mitochondrial membrane.
There the fatty acids, which like carbohydrates are relatively inert, must first be activated by conversion to an energy-rich fatty acid derivative of coenzyme A called fatty acyl-coenzyme A CoA.
The activation is catalyzed by acyl-CoA synthetase. For each molecule of fatty acid activated, one molecule of coenzyme A and one molecule of adenosine triphosphate ATP are used, equaling a net utilization of the two high-energy bonds in one ATP molecule which is therefore converted to adenosine monophosphate [AMP] rather than adenosine diphosphate [ADP] :.
The fatty acyl-CoA diffuses to the inner mitochondrial membrane, where it combines with a carrier molecule known as carnitine in a reaction catalyzed by carnitine acyltransferase. The acyl-carnitine derivative is transported into the mitochondrial matrix and converted back to the fatty acyl-CoA.
Further oxidation of the fatty acyl-CoA occurs in the mitochondrial matrix via a sequence of four reactions known collectively as β-oxidation A sequence of four reactions in which fatty acyl-CoA molecules are oxidized, leading to the removal of acetyl-CoA molecules.
because the β-carbon undergoes successive oxidations in the progressive removal of two carbon atoms from the carboxyl end of the fatty acyl-CoA Figure The fatty acyl-CoA formed in the final step becomes the substrate for the first step in the next round of β-oxidation.
β-oxidation continues until two acetyl-CoA molecules are produced in the final step. The first step in the catabolism of fatty acids is the formation of an alkene in an oxidation reaction catalyzed by acyl-CoA dehydrogenase.
In this reaction, the coenzyme FAD accepts two hydrogen atoms from the acyl-CoA, one from the α-carbon and one from the β-carbon, forming reduced flavin adenine dinucleotide FADH 2. The FADH 2 is reoxidized back to FAD via the electron transport chain.
For more information about the electron transport chain, see Section This supplies energy to form 1. Next, the trans -alkene is hydrated to form a secondary alcohol in a reaction catalyzed by enoyl-CoA hydratase.
The enzyme forms only the L-isomer. The final reaction is cleavage of the β-ketoacyl-CoA by a molecule of coenzyme A. The products are acetyl-CoA and a fatty acyl-CoA that has been shortened by two carbon atoms. The reaction is catalyzed by thiolase. The shortened fatty acyl-CoA is then degraded by repetitions of these four steps, each time releasing a molecule of acetyl-CoA.
The overall equation for the β-oxidation of palmitoyl-CoA 16 carbon atoms is as follows:. Because each shortened fatty acyl-CoA cycles back to the beginning of the pathway, β-oxidation is sometimes referred to as the fatty acid spiral. The fate of the acetyl-CoA obtained from fatty acid oxidation depends on the needs of an organism.
It may enter the citric acid cycle and be oxidized to produce energy, it may be used for the formation of water-soluble derivatives known as ketone bodies, or it may serve as the starting material for the synthesis of fatty acids. For more information about the citric acid cycle, see Section In the liver, most of the acetyl-CoA obtained from fatty acid oxidation is oxidized by the citric acid cycle.
However, some of the acetyl-CoA is used to synthesize a group of compounds known as ketone bodies : acetoacetate, β-hydroxybutyrate, and acetone.
Two acetyl-CoA molecules combine, in a reversal of the final step of β-oxidation, to produce acetoacetyl-CoA. The acetoacetyl-CoA reacts with another molecule of acetyl-CoA and water to form β-hydroxy-β-methylglutaryl-CoA, which is then cleaved to acetoacetate and acetyl-CoA.
Most of the acetoacetate is reduced to β-hydroxybutyrate, while a small amount is decarboxylated to carbon dioxide and acetone. The acetoacetate and β-hydroxybutyrate synthesized by the liver are released into the blood for use as a metabolic fuel to be converted back to acetyl-CoA by other tissues, particularly the kidney and the heart.
Under normal conditions, the kidneys excrete about 20 mg of ketone bodies each day, and the blood levels are maintained at about 1 mg of ketone bodies per mL of blood. In starvation, diabetes mellitus, and certain other physiological conditions in which cells do not receive sufficient amounts of carbohydrate, the rate of fatty acid oxidation increases to provide energy.
This leads to an increase in the concentration of acetyl-CoA. The increased acetyl-CoA cannot be oxidized by the citric acid cycle because of a decrease in the concentration of oxaloacetate, which is diverted to glucose synthesis.
In response, the rate of ketone body formation in the liver increases further, to a level much higher than can be used by other tissues. The excess ketone bodies accumulate in the blood and the urine, a condition referred to as ketosis.
When the acetone in the blood reaches the lungs, its volatility causes it to be expelled in the breath. The sweet smell of acetone, a characteristic of ketosis, is frequently noticed on the breath of severely diabetic patients.
Because two of the three kinds of ketone bodies are weak acids, their presence in the blood in excessive amounts overwhelms the blood buffers and causes a marked decrease in blood pH to 6. This decrease in pH leads to a serious condition known as acidosis.
One of the effects of acidosis is a decrease in the ability of hemoglobin to transport oxygen in the blood. In moderate to severe acidosis, breathing becomes labored and very painful.
The body also loses fluids and becomes dehydrated as the kidneys attempt to get rid of the acids by eliminating large quantities of water. The lowered oxygen supply and dehydration lead to depression; even mild acidosis leads to lethargy, loss of appetite, and a generally run-down feeling. Untreated patients may go into a coma.
The amount of ATP obtained from fatty acid oxidation depends on the size of the fatty acid being oxidized. For our purposes here. Calculating its energy yield provides a model for determining the ATP yield of all other fatty acids.
The breakdown by an organism of 1 mol of palmitic acid requires 1 mol of ATP for activation and forms 8 mol of acetyl-CoA.
Recall from Table The complete degradation of 1 mol of palmitic acid requires the β-oxidation reactions to be repeated seven times. Thus, 7 mol of NADH and 7 mol of FADH 2 are produced. Reoxidation of these compounds through respiration yields 2. The energy calculations can be summarized as follows:.
The combustion of 1 mol of palmitic acid releases a considerable amount of energy:. The percentage of this energy that is conserved by the cell in the form of ATP is as follows:. For more information about the efficiency of fatty acid metabolism, see Section The oxidation of fatty acids produces large quantities of water.
This water, which sustains migratory birds and animals such as the camel for long periods of time. How are fatty acids activated prior to being transported into the mitochondria and oxidized?
Draw the structure of hexanoic caproic acid and identify the α-carbon and the β-carbon. They react with CoA to form fatty acyl-CoA molecules. For each reaction found in β-oxidation, identify the enzyme that catalyzes the reaction and classify the reaction as oxidation-reduction, hydration, or cleavage.
How many rounds of β-oxidation are necessary to metabolize lauric acid a saturated fatty acid with 12 carbon atoms? How many rounds of β-oxidation are necessary to metabolize arachidic acid a saturated fatty acid with 20 carbon atoms?
When myristic acid a saturated fatty acid with 14 carbon atoms is completely oxidized by β-oxidation, how many molecules of each are formed?
When stearic acid a saturated fatty acid with 18 carbon atoms is completely oxidized by β-oxidation, how many molecules of each are formed? What is the net yield of ATP from the complete oxidation, in a liver cell, of one molecule of myristic acid?
What is the net yield of ATP from the complete oxidation, in a liver cell, of one molecule of stearic acid? The liver is the principal site of amino acid metabolism, but other tissues, such as the kidney, the small intestine, muscles, and adipose tissue, take part.
Generally, the first step in the breakdown of amino acids is the separation of the amino group from the carbon skeleton, usually by a transamination reaction. The carbon skeletons resulting from the deaminated amino acids are used to form either glucose or fats, or they are converted to a metabolic intermediate that can be oxidized by the citric acid cycle.
The latter alternative, amino acid catabolism, is more likely to occur when glucose levels are low—for example, when a person is fasting or starving. Transamination An exchange of functional groups between any amino acid and an α-keto acid.
is an exchange of functional groups between any amino acid except lysine, proline, and threonine and an α-keto acid. The amino group is usually transferred to the keto carbon atom of pyruvate, oxaloacetate, or α-ketoglutarate, converting the α-keto acid to alanine, aspartate, or glutamate, respectively.
Transamination reactions are catalyzed by specific transaminases also called aminotransferases , which require pyridoxal phosphate as a coenzyme. For more information about coenzymes, see Chapter 18 "Amino Acids, Proteins, and Enzymes" , Section Alanine and aspartate then undergo a second transamination reaction, transferring their amino groups to α-ketoglutarate and forming glutamate Figure In an α-keto acid, the carbonyl or keto group is located on the carbon atom adjacent to the carboxyl group of the acid.
For more information about acid carboxyl groups, see Chapter 15 "Organic Acids and Bases and Some of Their Derivatives" , Section In both reactions, the final acceptor of the amino group is α-ketoglutarate, and the final product is glutamate.
In the breakdown of amino acids for energy, the final acceptor of the α-amino group is α-ketoglutarate, forming glutamate. Glutamate can then undergo oxidative deamination A reaction in which glutamate loses its amino group as an ammonium ion and is oxidized back to α-ketoglutarate.
This reaction occurs primarily in liver mitochondria. The synthesis of glutamate occurs in animal cells by reversing the reaction catalyzed by glutamate dehydrogenase. For this reaction nicotinamide adenine dinucleotide phosphate NADPH acts as the reducing agent. The amino group can then be passed on through transamination reactions, to produce other amino acids from the appropriate α-keto acids.
Any amino acid can be converted into an intermediate of the citric acid cycle. Once the amino group is removed, usually by transamination, the α-keto acid that remains is catabolized by a pathway unique to that acid and consisting of one or more reactions. For example, phenylalanine undergoes a series of six reactions before it splits into fumarate and acetoacetate.
Fumarate is an intermediate in the citric acid cycle, while acetoacetate must be converted to acetoacetyl-coenzyme A CoA and then to acetyl-CoA before it enters the citric acid cycle.
Those amino acids that can form any of the intermediates of carbohydrate metabolism can subsequently be converted to glucose via a metabolic pathway known as gluconeogenesis. These amino acids are called glucogenic amino acids An amino acid that can form any of the intermediates of carbohydrate metabolism and subsequently be converted to glucose.
Amino acids that are converted to acetoacetyl-CoA or acetyl-CoA, which can be used for the synthesis of ketone bodies but not glucose, are called ketogenic amino acids An amino acid that is converted to acetoacetyl-CoA or acetyl-CoA, which can be used for the synthesis of ketone bodies but not glucose.
Some amino acids fall into both categories. Leucine and lysine are the only amino acids that are exclusively ketogenic. An exercise physiologist works with individuals who have or wish to prevent developing a wide variety of chronic diseases, such as diabetes, in which exercise has been shown to be beneficial.
Each individual must be referred by a licensed physician. An exercise physiologist works in a variety of settings, such as a hospital or in a wellness program at a commercial business, to design and monitor individual exercise plans. A registered clinical exercise physiologist must have an undergraduate degree in exercise physiology or a related degree.
Write the equation for the transamination reaction between valine and pyruvate. Write the equation for the transamination reaction between phenylalanine and oxaloacetate.
What products are formed in the oxidative deamination of glutamate? Determine if each amino acid is glucogenic, ketogenic, or both. To ensure that you understand the material in this chapter, you should review the meanings of the bold terms in the following summary and ask yourself how they relate to the topics in the chapter.
Metabolism is the general term for all chemical reactions in living organisms. The two types of metabolism are catabolism —those reactions in which complex molecules carbohydrates, lipids, and proteins are broken down to simpler ones with the concomitant release of energy—and anabolism —those reactions that consume energy to build complex molecules.
Metabolism is studied by looking at individual metabolic pathways , which are a series of biochemical reactions in which a given reactant is converted to a desired end product. The oxidation of fuel molecules primarily carbohydrates and lipids , a process called respiration , is the source of energy used by cells.
Catabolic reactions release energy from food molecules and use some of that energy for the synthesis of adenosine triphosphate ATP ; anabolic reactions use the energy in ATP to create new compounds. Catabolism can be divided into three stages. In stage I, carbohydrates, lipids, and proteins are broken down into their individual monomer units—simple sugars, fatty acids, and amino acids, respectively.
In stage II, these monomer units are broken down by specific metabolic pathways to form a common end product acetyl-coenzyme A CoA. In stage III, acetyl-CoA is completely oxidized to form carbon dioxide and water, and ATP is produced. The digestion of carbohydrates begins in the mouth as α-amylase breaks glycosidic linkages in carbohydrate molecules.
Essentially no carbohydrate digestion occurs in the stomach, and food particles pass through to the small intestine, where α-amylase and intestinal enzymes convert complex carbohydrate molecules starches to monosaccharides. The monosaccharides then pass through the lining of the small intestine and into the bloodstream for transport to all body cells.
Protein digestion begins in the stomach as pepsinogen in gastric juice is converted to pepsin, the enzyme that hydrolyzes peptide bonds.
The partially digested protein then passes to the small intestine, where the remainder of protein digestion takes place through the action of several enzymes.
The resulting amino acids cross the intestinal wall into the blood and are carried to the liver. Lipid digestion begins in the small intestine.
Bile salts emulsify the lipid molecules, and then lipases hydrolyze them to fatty acids and monoglycerides. The hydrolysis products pass through the intestine and are repackaged for transport in the bloodstream.
In cells that are operating aerobically, acetyl-CoA produced in stage II of catabolism is oxidized to carbon dioxide. The citric acid cycle describes this oxidation, which takes place with the formation of the coenzymes reduced nicotinamide adenine dinucleotide NADH and reduced flavin adenine dinucleotide FADH 2.
The sequence of reactions needed to oxidize these coenzymes and transfer the resulting electrons to oxygen is called the electron transport chain , or the respiratory chain.
The compounds responsible for this series of oxidation-reduction reactions include proteins known as cytochromes , Fe·S proteins, and other molecules that ultimately result in the reduction of molecular oxygen to water. Every time a compound with two carbon atoms is oxidized in the citric acid cycle, a respiratory chain compound accepts the electrons lost in the oxidation and so is reduced and then passes them on to the next metabolite in the chain.
Electron transport and oxidative phosphorylation are tightly coupled to each other. The enzymes and intermediates of the citric acid cycle, the electron transport chain, and oxidative phosphorylation are located in organelles called mitochondria. Glucose is oxidized to two molecules of pyruvate through a series of reactions known as glycolysis.
Some of the energy released in these reactions is conserved by the formation of ATP from ADP. The pyruvate produced by glycolysis has several possible fates, depending on the organism and whether or not oxygen is present. In animal cells, pyruvate can be further oxidized to acetyl-CoA and then to carbon dioxide through the citric acid cycle if oxygen supplies are sufficient.
When oxygen supplies are insufficient, pyruvate is reduced to lactate. In yeast and other microorganisms, pyruvate is not converted to lactate in the absence of oxygen but instead is converted to ethanol and carbon dioxide.
The amount of ATP formed by the oxidation of glucose depends on whether or not oxygen is present. If oxygen is present, glucose is oxidized to carbon dioxide, and 36—38 ATP molecules are produced for each glucose molecule oxidized, using the combined pathways of glycolysis, the citric acid cycle, the electron transport chain, and oxidative phosphorylation.
Fatty acids, released by the degradation of triglycerides and other lipids, are converted to fatty acyl-CoA, transported into the mitochondria, and oxidized by repeated cycling through a sequence of four reactions known as β - oxidation.
In each round of β-oxidation, the fatty acyl-CoA is shortened by two carbon atoms as one molecule of acetyl-CoA is formed. The final round of β-oxidation, once the chain has been shortened to four carbon atoms, forms two molecules of acetyl-CoA.
β-oxidation also forms the reduced coenzymes FADH 2 and NADH, whose reoxidation through the electron transport chain and oxidative phosphorylation leads to the synthesis of ATP.
Thank you for visiting nature. Eneergy are Energy storage advancements Energy metabolism browser version with limited support for CSS. To mstabolism the best metaolism, we recommend Protein intake and hair growth use a Enwrgy up to metabolis, browser or turn off compatibility mode in Internet Explorer. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. Energy metabolism is the process of generating energy ATP from nutrients. Metabolism comprises a series of interconnected pathways that can function in the presence or absence of oxygen. Aerobic metabolism converts one glucose molecule into ATP molecules.
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