No additional carbons are removed prior to the production of fumarate, and therefore, fumarate contains four atoms of carbon. The citric acid cycle intermediate, malate , contains four atoms of carbon. A single glucose molecule, which is the starting material for glycolysis, contains six carbon atoms. Glycolysis produces two pyruvate molecules, and one pyruvate molecule contains three carbon atoms.
Prior to entering the citric acid cycle, pyruvate loses one carbon dioxide molecule e. Acetyl-CoA then combines with one oxaloacetate molecule, a four- carbon molecule, to produce a molecule of citrate , which contains six carbon atoms, and is the starting material for the citric acid cycle.
Citrate undergoes a number of a reactions in the citric acid cycle, including two reactions where one atom of carbon dioxide e. No additional carbons are removed prior to the production of malate.
Therefore, malate contains four atoms of carbon. Which of the following statements about the citric acid cycle is true? There is only one decarboxylation in the cycle. Acetyl-CoA is one of the compounds in the cycle.
None of the other answers are true. Isocitrate is one of the compounds in the cycle. Two equivalents of are produced in the cycle. Acetyl-CoA is not part of the cycle but is oxidized by it. There are two decarboxylations in the cycle, from isocitrate to alpha-ketoglutarate, and from alpha-ketoglutarate to succinyl-CoA. In total, three equivalents of are produced in the cycle.
Isocitrate is a compound in the cycle, produced from citrate. Which of the following steps in the citric acid cycle do not have a largely negative? None of these reactions have largely negative values. Even though an is generated when malate is dehydrogenated to oxaloacetate, this oxidation is very unfavorable because of the addition of a reactive ketone in place of an alcohol on the 2nd carbon.
In fact, the only way this reaction can proceed is if oxaloacetate concentration is very low. All of the other reactions have large negative values. Which reaction of the citric acid cycle makes the entire process unidirectional i. Alpha-ketoglutarate succinyl-CoA. Isocitrate alpha-ketoglutarate. Succinate fumarate. Succinyl-CoA malate. Citrate isocitrate. The formation of alpha-ketoglutarate from isocitrate using the enzyme alpha-ketoglutarate dehydrogenase is an irreversible reaction due to its largely negative value.
Suppose that in a certain neuron, an action potential has caused ions to enter the cell. In order to restore the resting membrane potential, the sodium-potassium pump uses 1 molecule of ATP to push ions out of the cell and to bring ions into the cell.
How many molecules of acetyl-CoA must pass through the citric acid cycle in order to provide enough energy for this process to occur? This question is providing us with a scenario in which ions enter a cell.
We're further told that it will take a single molecule of ATP to move three of these ions out of the cell. Finally, we are being asked to determine the total number of acetyl-CoA molecules that must pass through the Krebs cycle in order to provide the energy necessary for the export of these ions.
First, we'll need to determine the total number of ATP molecules generated from the passage of a single molecule of acetyl-CoA through the Krebs cycle. It's important to remember that the passage of acetyl-CoA through the Krebs cycle generates one molecule of ATP directly by substrate-level phosphorylation, but it also produces other intermediate energy carriers in the form of and.
For each acetyl-CoA ran through the cycle, one molecule of and three molecules of are produced. Furthermore, each molecule of will go on to donate its electrons to the electron transport chain to generate molecules of ATP per molecule of oxidized.
Likewise, each will also produce ATP via oxidative phosphorylation, but at a rate of molecules of ATP per molecule of oxidized. ATP via substrate-level phosphorylation. Adding these values up, we have a total of molecules of ATP produced for every molecule of acetyl-CoA oxidized. Now that we know how much ATP is produced from one acetyl-CoA, we can calculate the number needed to move the ions out of the cell.
In this reaction, succinyl-CoA is converted to succinate with the assistance of the enzyme, succinyl-CoA synthetase. Thus, the overall reaction appears as:. While side products of some of the other reactions listed produce intermediaries that may be used to produce ATP in the future, these reactions do not directly produce ATP.
The citrate will then harvest the remainder of the extractable energy from what began as a glucose molecule and continue through the citric acid cycle. In the citric acid cycle, the two carbons that were originally the acetyl group of acetyl CoA are released as carbon dioxide, one of the major products of cellular respiration, through a series of enzymatic reactions. In addition to the citric acid cycle, named for the first intermediate formed, citric acid, or citrate, when acetate joins to the oxaloacetate, the cycle is also known by two other names.
In order for pyruvate, the product of glycolysis, to enter the next pathway, it must undergo several changes to become acetyl Coenzyme A acetyl CoA. Acetyl CoA is a molecule that is further converted to oxaloacetate, which enters the citric acid cycle Krebs cycle. The conversion of pyruvate to acetyl CoA is a three-step process. Breakdown of Pyruvate : Each pyruvate molecule loses a carboxylic group in the form of carbon dioxide.
Step 1. A carboxyl group is removed from pyruvate, releasing a molecule of carbon dioxide into the surrounding medium. Note: carbon dioxide is one carbon attached to two oxygen atoms and is one of the major end products of cellular respiration.
The result of this step is a two-carbon hydroxyethyl group bound to the enzyme pyruvate dehydrogenase; the lost carbon dioxide is the first of the six carbons from the original glucose molecule to be removed. This step proceeds twice for every molecule of glucose metabolized remember: there are two pyruvate molecules produced at the end of glycolysis ; thus, two of the six carbons will have been removed at the end of both of these steps.
Step 2. Step 3. The enzyme-bound acetyl group is transferred to CoA, producing a molecule of acetyl CoA. This molecule of acetyl CoA is then further converted to be used in the next pathway of metabolism, the citric acid cycle. Acetyl CoA links glycolysis and pyruvate oxidation with the citric acid cycle. In the presence of oxygen, acetyl CoA delivers its acetyl group to a four-carbon molecule, oxaloacetate, to form citrate, a six-carbon molecule with three carboxyl groups.
During this first step of the citric acid cycle, the CoA enzyme, which contains a sulfhydryl group -SH , is recycled and becomes available to attach another acetyl group. The citrate will then harvest the remainder of the extractable energy from what began as a glucose molecule and continue through the citric acid cycle. In the citric acid cycle, the two carbons that were originally the acetyl group of acetyl CoA are released as carbon dioxide, one of the major products of cellular respiration, through a series of enzymatic reactions.
Acetyl CoA and the Citric Acid Cycle : For each molecule of acetyl CoA that enters the citric acid cycle, two carbon dioxide molecules are released, removing the carbons from the acetyl group. In addition to the citric acid cycle, named for the first intermediate formed, citric acid, or citrate, when acetate joins to the oxaloacetate, the cycle is also known by two other names. The TCA cycle is named for tricarboxylic acids TCA because citric acid or citrate and isocitrate, the first two intermediates that are formed, are tricarboxylic acids.
Additionally, the cycle is known as the Krebs cycle, named after Hans Krebs, who first identified the steps in the pathway in the s in pigeon flight muscle. Like the conversion of pyruvate to acetyl CoA, the citric acid cycle takes place in the matrix of the mitochondria.
Almost all of the enzymes of the citric acid cycle are soluble, with the single exception of the enzyme succinate dehydrogenase, which is embedded in the inner membrane of the mitochondrion. Unlike glycolysis, the citric acid cycle is a closed loop: the last part of the pathway regenerates the compound used in the first step. This is considered an aerobic pathway because the NADH and FADH2 produced must transfer their electrons to the next pathway in the system, which will use oxygen.
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